1 .TH LIBPNG 3 "February 14, 2013"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.6.0
8 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
10 \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
12 \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
14 \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
16 \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
18 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
20 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
22 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
24 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
26 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
28 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
30 \fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
32 \fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
34 \fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
36 \fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
38 \fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
40 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
42 \fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
44 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
46 \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
48 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
50 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
52 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
54 \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
56 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
58 \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
60 \fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
62 \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
64 \fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
66 \fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
68 \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fP\fI*red_Z\fP\fB, double \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fP\fI*blue_X\fP\fB, double \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
70 \fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
72 \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
74 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
76 \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
78 \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
80 \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
82 \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
84 \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
86 \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
88 \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
90 \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
92 \fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
94 \fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
96 \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
98 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
100 \fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
102 \fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
104 \fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
106 \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
108 \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
110 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
112 \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
114 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
116 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
118 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
120 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
122 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
124 \fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
126 \fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
128 \fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
130 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
132 \fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
134 \fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
136 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
138 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
140 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
142 \fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
144 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
146 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
148 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
150 \fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
152 \fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
154 \fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
156 \fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
158 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
160 \fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
162 \fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
164 \fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
166 \fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
168 \fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
170 \fB/* This function is really an inline macro. \fI*/
172 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
174 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
176 \fB/* This function is really an inline macro. \fI*/
178 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
180 \fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
182 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
184 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
186 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
188 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
190 \fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
192 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
194 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
196 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
198 \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
200 \fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
202 \fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
204 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
206 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
208 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
210 \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
212 \fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
214 \fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
216 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
218 \fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
220 \fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
222 \fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, png_size_t \fIsize\fP\fB);\fP
224 \fBint png_image_finish_read (png_imagep \fP\fIimage\fP\fB, png_colorp \fP\fIbackground\fP\fB, void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
226 \fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
228 \fBint png_image_write_to_file (png_imagep \fP\fIimage\fP\fB, const char \fP\fI*file\fP\fB, int \fP\fIconvert_to_8bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
230 \fBint png_image_write_to_stdio (png_imagep \fP\fIimage\fP\fB, FILE \fP\fI*file\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap)\fP\fB);\fP
232 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
234 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
236 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
238 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
240 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
242 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
244 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
246 \fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
248 \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
250 \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
252 \fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
254 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
256 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
258 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
260 \fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
262 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
264 \fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
266 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
268 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
270 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
272 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
274 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
276 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
278 \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
280 \fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
282 \fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
284 \fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
286 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
288 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
290 \fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
292 \fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
294 \fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
296 \fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
298 \fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fP\fIgreen_Y\fP\fB, double \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
300 \fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
302 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
304 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
306 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
308 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
310 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
312 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
314 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
316 \fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
318 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
320 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
322 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
324 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
326 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
328 \fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
330 \fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
332 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
334 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
336 \fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
338 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
340 \fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
342 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
344 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
346 \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
348 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
350 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
352 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
354 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
356 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
358 \fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
360 \fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
362 \fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
364 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
366 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
368 \fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
370 \fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
372 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
374 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
376 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
378 \fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
380 \fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
382 \fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
384 \fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
386 \fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
388 \fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
390 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
392 \fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
394 \fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
396 \fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
398 \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
400 \fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
402 \fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
404 \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
406 \fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
408 \fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
410 \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
412 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
414 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
416 \fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
418 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
420 \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
422 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
424 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
426 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
428 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
430 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
432 \fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
434 \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
436 \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
438 \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
440 \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
442 \fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
444 \fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
446 \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
448 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
450 \fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
452 \fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
454 \fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
456 \fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
458 \fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
460 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
462 \fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
464 \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
466 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
468 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
470 \fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
472 \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
474 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
476 \fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
478 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
480 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
482 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
484 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
486 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
488 \fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
490 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
492 \fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
494 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
499 library supports encoding, decoding, and various manipulations of
500 the Portable Network Graphics (PNG) format image files. It uses the
503 Following is a copy of the libpng-manual.txt file that accompanies libpng.
505 libpng-manual.txt - A description on how to use and modify libpng
507 libpng version 1.6.0 - February 14, 2013
508 Updated and distributed by Glenn Randers-Pehrson
509 <glennrp at users.sourceforge.net>
510 Copyright (c) 1998-2013 Glenn Randers-Pehrson
512 This document is released under the libpng license.
513 For conditions of distribution and use, see the disclaimer
518 libpng versions 0.97, January 1998, through 1.6.0 - February 14, 2013
519 Updated and distributed by Glenn Randers-Pehrson
520 Copyright (c) 1998-2013 Glenn Randers-Pehrson
522 libpng 1.0 beta 6 version 0.96 May 28, 1997
523 Updated and distributed by Andreas Dilger
524 Copyright (c) 1996, 1997 Andreas Dilger
526 libpng 1.0 beta 2 - version 0.88 January 26, 1996
527 For conditions of distribution and use, see copyright
528 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
529 Schalnat, Group 42, Inc.
531 Updated/rewritten per request in the libpng FAQ
532 Copyright (c) 1995, 1996 Frank J. T. Wojcik
533 December 18, 1995 & January 20, 1996
542 VI. Modifying/Customizing libpng
544 VIII. Changes to Libpng from version 0.88
545 IX. Changes to Libpng from version 1.0.x to 1.2.x
546 X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
547 XI. Changes to Libpng from version 1.4.x to 1.5.x
548 XII. Changes to Libpng from version 1.5.x to 1.6.x
549 XIII. Detecting libpng
550 XIV. Source code repository
552 XVI. Y2K Compliance in libpng
556 This file describes how to use and modify the PNG reference library
557 (known as libpng) for your own use. There are five sections to this
558 file: introduction, structures, reading, writing, and modification and
559 configuration notes for various special platforms. In addition to this
560 file, example.c is a good starting point for using the library, as
561 it is heavily commented and should include everything most people
562 will need. We assume that libpng is already installed; see the
563 INSTALL file for instructions on how to install libpng.
565 For examples of libpng usage, see the files "example.c", "pngtest.c",
566 and the files in the "contrib" directory, all of which are included in
567 the libpng distribution.
569 Libpng was written as a companion to the PNG specification, as a way
570 of reducing the amount of time and effort it takes to support the PNG
571 file format in application programs.
573 The PNG specification (second edition), November 2003, is available as
574 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
575 <http://www.w3.org/TR/2003/REC-PNG-20031110/
576 The W3C and ISO documents have identical technical content.
578 The PNG-1.2 specification is available at
579 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
580 to the PNG specification (second edition) but has some additional material.
582 The PNG-1.0 specification is available
583 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
584 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
586 Some additional chunks are described in the special-purpose public chunks
587 documents at <http://www.libpng.org/pub/png/documents/>.
590 about PNG, and the latest version of libpng, can be found at the PNG home
591 page, <http://www.libpng.org/pub/png/>.
593 Most users will not have to modify the library significantly; advanced
594 users may want to modify it more. All attempts were made to make it as
595 complete as possible, while keeping the code easy to understand.
596 Currently, this library only supports C. Support for other languages
599 Libpng has been designed to handle multiple sessions at one time,
600 to be easily modifiable, to be portable to the vast majority of
601 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
602 to use. The ultimate goal of libpng is to promote the acceptance of
603 the PNG file format in whatever way possible. While there is still
604 work to be done (see the TODO file), libpng should cover the
605 majority of the needs of its users.
607 Libpng uses zlib for its compression and decompression of PNG files.
608 Further information about zlib, and the latest version of zlib, can
609 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
610 The zlib compression utility is a general purpose utility that is
611 useful for more than PNG files, and can be used without libpng.
612 See the documentation delivered with zlib for more details.
613 You can usually find the source files for the zlib utility wherever you
614 find the libpng source files.
616 Libpng is thread safe, provided the threads are using different
617 instances of the structures. Each thread should have its own
618 png_struct and png_info instances, and thus its own image.
619 Libpng does not protect itself against two threads using the
620 same instance of a structure.
624 There are two main structures that are important to libpng, png_struct
625 and png_info. Both are internal structures that are no longer exposed
626 in the libpng interface (as of libpng 1.5.0).
628 The png_info structure is designed to provide information about the
629 PNG file. At one time, the fields of png_info were intended to be
630 directly accessible to the user. However, this tended to cause problems
631 with applications using dynamically loaded libraries, and as a result
632 a set of interface functions for png_info (the png_get_*() and png_set_*()
633 functions) was developed, and direct access to the png_info fields was
636 The png_struct structure is the object used by the library to decode a
637 single image. As of 1.5.0 this structure is also not exposed.
639 Almost all libpng APIs require a pointer to a png_struct as the first argument.
640 Many (in particular the png_set and png_get APIs) also require a pointer
641 to png_info as the second argument. Some application visible macros
642 defined in png.h designed for basic data access (reading and writing
643 integers in the PNG format) don't take a png_info pointer, but it's almost
644 always safe to assume that a (png_struct*) has to be passed to call an API
647 You can have more than one png_info structure associated with an image,
648 as illustrated in pngtest.c, one for information valid prior to the
649 IDAT chunks and another (called "end_info" below) for things after them.
651 The png.h header file is an invaluable reference for programming with libpng.
652 And while I'm on the topic, make sure you include the libpng header file:
656 and also (as of libpng-1.5.0) the zlib header file, if you need it:
662 The png.h header file defines a number of integral types used by the
663 APIs. Most of these are fairly obvious; for example types corresponding
664 to integers of particular sizes and types for passing color values.
666 One exception is how non-integral numbers are handled. For application
667 convenience most APIs that take such numbers have C (double) arguments;
668 however, internally PNG, and libpng, use 32 bit signed integers and encode
669 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
670 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
671 which is simply (png_int_32).
673 All APIs that take (double) arguments also have a matching API that
674 takes the corresponding fixed point integer arguments. The fixed point
675 API has the same name as the floating point one with "_fixed" appended.
676 The actual range of values permitted in the APIs is frequently less than
677 the full range of (png_fixed_point) (-21474 to +21474). When APIs require
678 a non-negative argument the type is recorded as png_uint_32 above. Consult
679 the header file and the text below for more information.
681 Special care must be take with sCAL chunk handling because the chunk itself
682 uses non-integral values encoded as strings containing decimal floating point
683 numbers. See the comments in the header file.
687 The main header file function declarations are frequently protected by C
688 preprocessing directives of the form:
690 #ifdef PNG_feature_SUPPORTED
694 #ifdef PNG_feature_SUPPORTED
698 The library can be built without support for these APIs, although a
699 standard build will have all implemented APIs. Application programs
700 should check the feature macros before using an API for maximum
701 portability. From libpng 1.5.0 the feature macros set during the build
702 of libpng are recorded in the header file "pnglibconf.h" and this file
703 is always included by png.h.
705 If you don't need to change the library configuration from the default, skip to
706 the next section ("Reading").
708 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
709 of the build project files in the 'projects' directory simply copy
710 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
711 systems do not permit easy auto-configuration of the library - they only
712 support the default configuration.
714 The easiest way to make minor changes to the libpng configuration when
715 auto-configuration is supported is to add definitions to the command line
716 using (typically) CPPFLAGS. For example:
718 CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
720 will change the internal libpng math implementation for gamma correction and
721 other arithmetic calculations to fixed point, avoiding the need for fast
722 floating point support. The result can be seen in the generated pnglibconf.h -
723 make sure it contains the changed feature macro setting.
725 If you need to make more extensive configuration changes - more than one or two
726 feature macro settings - you can either add -DPNG_USER_CONFIG to the build
727 command line and put a list of feature macro settings in pngusr.h or you can set
728 DFA_XTRA (a makefile variable) to a file containing the same information in the
729 form of 'option' settings.
731 A. Changing pnglibconf.h
733 A variety of methods exist to build libpng. Not all of these support
734 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
735 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
737 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
738 pnglibconf.h and changing the lines defining the supported features, paying
739 very close attention to the 'option' information in scripts/pnglibconf.dfa
740 that describes those features and their requirements. This is easy to get
743 B. Configuration using DFA_XTRA
745 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
746 variant such as 'nawk' or 'gawk', is available. The configure build will
747 automatically find an appropriate awk and build pnglibconf.h.
748 The scripts/pnglibconf.mak file contains a set of make rules for doing the
749 same thing if configure is not used, and many of the makefiles in the scripts
750 directory use this approach.
752 When rebuilding simply write a new file containing changed options and set
753 DFA_XTRA to the name of this file. This causes the build to append the new file
754 to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
755 of the following forms:
759 This turns all optional features off. Include it at the start of pngusr.dfa to
760 make it easier to build a minimal configuration. You will need to turn at least
761 some features on afterward to enable either reading or writing code, or both.
766 Enable or disable a single feature. This will automatically enable other
767 features required by a feature that is turned on or disable other features that
768 require a feature which is turned off. Conflicting settings will cause an error
769 message to be emitted by awk.
771 setting feature default value
773 Changes the default value of setting 'feature' to 'value'. There are a small
774 number of settings listed at the top of pnglibconf.h, they are documented in the
775 source code. Most of these values have performance implications for the library
776 but most of them have no visible effect on the API. Some can also be overridden
779 This method of building a customized pnglibconf.h is illustrated in
780 contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
781 pngusr.dfa in these directories.
783 C. Configuration using PNG_USR_CONFIG
785 If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
786 pngusr.h will automatically be included before the options in
787 scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
788 macro definitions turning features on or off or setting settings.
790 Apart from the global setting "everything = off" all the options listed above
791 can be set using macros in pngusr.h:
793 #define PNG_feature_SUPPORTED
799 #define PNG_NO_feature
805 #define PNG_feature value
809 setting feature default value
811 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
812 pngusr file you supply override the contents of scripts/pnglibconf.dfa
814 If confusing or incomprehensible behavior results it is possible to
815 examine the intermediate file pnglibconf.dfn to find the full set of
816 dependency information for each setting and option. Simply locate the
817 feature in the file and read the C comments that precede it.
819 This method is also illustrated in the contrib/pngminim/* makefiles and
824 We'll now walk you through the possible functions to call when reading
825 in a PNG file sequentially, briefly explaining the syntax and purpose
826 of each one. See example.c and png.h for more detail. While
827 progressive reading is covered in the next section, you will still
828 need some of the functions discussed in this section to read a PNG
833 You will want to do the I/O initialization(*) before you get into libpng,
834 so if it doesn't work, you don't have much to undo. Of course, you
835 will also want to insure that you are, in fact, dealing with a PNG
836 file. Libpng provides a simple check to see if a file is a PNG file.
837 To use it, pass in the first 1 to 8 bytes of the file to the function
838 png_sig_cmp(), and it will return 0 (false) if the bytes match the
839 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
840 Of course, the more bytes you pass in, the greater the accuracy of the
843 If you are intending to keep the file pointer open for use in libpng,
844 you must ensure you don't read more than 8 bytes from the beginning
845 of the file, and you also have to make a call to png_set_sig_bytes_read()
846 with the number of bytes you read from the beginning. Libpng will
847 then only check the bytes (if any) that your program didn't read.
849 (*): If you are not using the standard I/O functions, you will need
850 to replace them with custom functions. See the discussion under
854 FILE *fp = fopen(file_name, "rb");
860 fread(header, 1, number, fp);
861 is_png = !png_sig_cmp(header, 0, number);
869 Next, png_struct and png_info need to be allocated and initialized. In
870 order to ensure that the size of these structures is correct even with a
871 dynamically linked libpng, there are functions to initialize and
872 allocate the structures. We also pass the library version, optional
873 pointers to error handling functions, and a pointer to a data struct for
874 use by the error functions, if necessary (the pointer and functions can
875 be NULL if the default error handlers are to be used). See the section
876 on Changes to Libpng below regarding the old initialization functions.
877 The structure allocation functions quietly return NULL if they fail to
878 create the structure, so your application should check for that.
880 png_structp png_ptr = png_create_read_struct
881 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
882 user_error_fn, user_warning_fn);
887 png_infop info_ptr = png_create_info_struct(png_ptr);
891 png_destroy_read_struct(&png_ptr,
892 (png_infopp)NULL, (png_infopp)NULL);
896 If you want to use your own memory allocation routines,
897 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
898 png_create_read_struct_2() instead of png_create_read_struct():
900 png_structp png_ptr = png_create_read_struct_2
901 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
902 user_error_fn, user_warning_fn, (png_voidp)
903 user_mem_ptr, user_malloc_fn, user_free_fn);
905 The error handling routines passed to png_create_read_struct()
906 and the memory alloc/free routines passed to png_create_struct_2()
907 are only necessary if you are not using the libpng supplied error
908 handling and memory alloc/free functions.
910 When libpng encounters an error, it expects to longjmp back
911 to your routine. Therefore, you will need to call setjmp and pass
912 your png_jmpbuf(png_ptr). If you read the file from different
913 routines, you will need to update the longjmp buffer every time you enter
914 a new routine that will call a png_*() function.
916 See your documentation of setjmp/longjmp for your compiler for more
917 information on setjmp/longjmp. See the discussion on libpng error
918 handling in the Customizing Libpng section below for more information
919 on the libpng error handling. If an error occurs, and libpng longjmp's
920 back to your setjmp, you will want to call png_destroy_read_struct() to
923 if (setjmp(png_jmpbuf(png_ptr)))
925 png_destroy_read_struct(&png_ptr, &info_ptr,
931 Pass (png_infopp)NULL instead of &end_info if you didn't create
932 an end_info structure.
934 If you would rather avoid the complexity of setjmp/longjmp issues,
935 you can compile libpng with PNG_NO_SETJMP, in which case
936 errors will result in a call to PNG_ABORT() which defaults to abort().
938 You can #define PNG_ABORT() to a function that does something
939 more useful than abort(), as long as your function does not
942 Now you need to set up the input code. The default for libpng is to
943 use the C function fread(). If you use this, you will need to pass a
944 valid FILE * in the function png_init_io(). Be sure that the file is
945 opened in binary mode. If you wish to handle reading data in another
946 way, you need not call the png_init_io() function, but you must then
947 implement the libpng I/O methods discussed in the Customizing Libpng
950 png_init_io(png_ptr, fp);
952 If you had previously opened the file and read any of the signature from
953 the beginning in order to see if this was a PNG file, you need to let
954 libpng know that there are some bytes missing from the start of the file.
956 png_set_sig_bytes(png_ptr, number);
958 You can change the zlib compression buffer size to be used while
959 reading compressed data with
961 png_set_compression_buffer_size(png_ptr, buffer_size);
963 where the default size is 8192 bytes. Note that the buffer size
964 is changed immediately and the buffer is reallocated immediately,
965 instead of setting a flag to be acted upon later.
967 If you want CRC errors to be handled in a different manner than
970 png_set_crc_action(png_ptr, crit_action, ancil_action);
972 The values for png_set_crc_action() say how libpng is to handle CRC errors in
973 ancillary and critical chunks, and whether to use the data contained
974 therein. Note that it is impossible to "discard" data in a critical
977 Choices for (int) crit_action are
978 PNG_CRC_DEFAULT 0 error/quit
979 PNG_CRC_ERROR_QUIT 1 error/quit
980 PNG_CRC_WARN_USE 3 warn/use data
981 PNG_CRC_QUIET_USE 4 quiet/use data
982 PNG_CRC_NO_CHANGE 5 use the current value
984 Choices for (int) ancil_action are
985 PNG_CRC_DEFAULT 0 error/quit
986 PNG_CRC_ERROR_QUIT 1 error/quit
987 PNG_CRC_WARN_DISCARD 2 warn/discard data
988 PNG_CRC_WARN_USE 3 warn/use data
989 PNG_CRC_QUIET_USE 4 quiet/use data
990 PNG_CRC_NO_CHANGE 5 use the current value
992 .SS Setting up callback code
994 You can set up a callback function to handle any unknown chunks in the
995 input stream. You must supply the function
997 read_chunk_callback(png_structp png_ptr,
998 png_unknown_chunkp chunk);
1000 /* The unknown chunk structure contains your
1001 chunk data, along with similar data for any other
1008 /* Note that libpng has already taken care of
1011 /* put your code here. Search for your chunk in the
1012 unknown chunk structure, process it, and return one
1013 of the following: */
1015 return (-n); /* chunk had an error */
1016 return (0); /* did not recognize */
1017 return (n); /* success */
1020 (You can give your function another name that you like instead of
1021 "read_chunk_callback")
1023 To inform libpng about your function, use
1025 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1026 read_chunk_callback);
1028 This names not only the callback function, but also a user pointer that
1029 you can retrieve with
1031 png_get_user_chunk_ptr(png_ptr);
1033 If you call the png_set_read_user_chunk_fn() function, then all unknown
1034 chunks will be saved when read, in case your callback function will need
1035 one or more of them. This behavior can be changed with the
1036 png_set_keep_unknown_chunks() function, described below.
1038 At this point, you can set up a callback function that will be
1039 called after each row has been read, which you can use to control
1040 a progress meter or the like. It's demonstrated in pngtest.c.
1041 You must supply a function
1043 void read_row_callback(png_structp png_ptr,
1044 png_uint_32 row, int pass);
1046 /* put your code here */
1049 (You can give it another name that you like instead of "read_row_callback")
1051 To inform libpng about your function, use
1053 png_set_read_status_fn(png_ptr, read_row_callback);
1055 When this function is called the row has already been completely processed and
1056 the 'row' and 'pass' refer to the next row to be handled. For the
1057 non-interlaced case the row that was just handled is simply one less than the
1058 passed in row number, and pass will always be 0. For the interlaced case the
1059 same applies unless the row value is 0, in which case the row just handled was
1060 the last one from one of the preceding passes. Because interlacing may skip a
1061 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1062 need to know what the last pass is record (row,pass) from the callback and use
1063 the last recorded value each time.
1065 As with the user transform you can find the output row using the
1066 PNG_ROW_FROM_PASS_ROW macro.
1068 .SS Unknown-chunk handling
1070 Now you get to set the way the library processes unknown chunks in the
1071 input PNG stream. Both known and unknown chunks will be read. Normal
1072 behavior is that known chunks will be parsed into information in
1073 various info_ptr members while unknown chunks will be discarded. This
1074 behavior can be wasteful if your application will never use some known
1075 chunk types. To change this, you can call:
1077 png_set_keep_unknown_chunks(png_ptr, keep,
1078 chunk_list, num_chunks);
1080 keep - 0: default unknown chunk handling
1081 1: ignore; do not keep
1082 2: keep only if safe-to-copy
1083 3: keep even if unsafe-to-copy
1085 You can use these definitions:
1086 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1087 PNG_HANDLE_CHUNK_NEVER 1
1088 PNG_HANDLE_CHUNK_IF_SAFE 2
1089 PNG_HANDLE_CHUNK_ALWAYS 3
1091 chunk_list - list of chunks affected (a byte string,
1092 five bytes per chunk, NULL or '\0' if
1093 num_chunks is positive; ignored if
1096 num_chunks - number of chunks affected; if 0, all
1097 unknown chunks are affected. If positive,
1098 only the chunks in the list are affected,
1099 and if negative all unknown chunks and
1100 all known chunks except for the IHDR,
1101 PLTE, tRNS, IDAT, and IEND chunks are
1104 Unknown chunks declared in this way will be saved as raw data onto a
1105 list of png_unknown_chunk structures. If a chunk that is normally
1106 known to libpng is named in the list, it will be handled as unknown,
1107 according to the "keep" directive. If a chunk is named in successive
1108 instances of png_set_keep_unknown_chunks(), the final instance will
1109 take precedence. The IHDR and IEND chunks should not be named in
1110 chunk_list; if they are, libpng will process them normally anyway.
1111 If you know that your application will never make use of some particular
1112 chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1114 Here is an example of the usage of png_set_keep_unknown_chunks(),
1115 where the private "vpAg" chunk will later be processed by a user chunk
1118 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1120 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1121 png_byte unused_chunks[]=
1123 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1124 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1125 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1126 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1127 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1128 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1134 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1135 /* ignore all unknown chunks: */
1136 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1138 /* except for vpAg: */
1139 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1141 /* also ignore unused known chunks: */
1142 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1143 (int)sizeof(unused_chunks)/5);
1148 The PNG specification allows the width and height of an image to be as
1149 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1150 Since very few applications really need to process such large images,
1151 we have imposed an arbitrary 1-million limit on rows and columns.
1152 Larger images will be rejected immediately with a png_error() call. If
1153 you wish to change this limit, you can use
1155 png_set_user_limits(png_ptr, width_max, height_max);
1157 to set your own limits, or use width_max = height_max = 0x7fffffffL
1158 to allow all valid dimensions (libpng may reject some very large images
1159 anyway because of potential buffer overflow conditions).
1161 You should put this statement after you create the PNG structure and
1162 before calling png_read_info(), png_read_png(), or png_process_data().
1164 When writing a PNG datastream, put this statement before calling
1165 png_write_info() or png_write_png().
1167 If you need to retrieve the limits that are being applied, use
1169 width_max = png_get_user_width_max(png_ptr);
1170 height_max = png_get_user_height_max(png_ptr);
1172 The PNG specification sets no limit on the number of ancillary chunks
1173 allowed in a PNG datastream. You can impose a limit on the total number
1174 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1176 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1178 where 0x7fffffffL means unlimited. You can retrieve this limit with
1180 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1182 You can also set a limit on the amount of memory that a compressed chunk
1183 other than IDAT can occupy, with
1185 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1187 and you can retrieve the limit with
1189 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1191 Any chunks that would cause either of these limits to be exceeded will
1194 .SS Information about your system
1196 If you intend to display the PNG or to incorporate it in other image data you
1197 need to tell libpng information about your display or drawing surface so that
1198 libpng can convert the values in the image to match the display.
1200 From libpng-1.5.4 this information can be set before reading the PNG file
1201 header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1202 called before the PNG file header had been read and png_set_alpha_mode() did not
1205 If you need to support versions prior to libpng-1.5.4 test the version number
1206 as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1207 described in the appropriate manual page.
1209 You give libpng the encoding expected by your system expressed as a 'gamma'
1210 value. You can also specify a default encoding for the PNG file in
1211 case the required information is missing from the file. By default libpng
1212 assumes that the PNG data matches your system, to keep this default call:
1214 png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
1216 or you can use the fixed point equivalent:
1218 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
1219 PNG_FP_1/screen_gamma);
1221 If you don't know the gamma for your system it is probably 2.2 - a good
1222 approximation to the IEC standard for display systems (sRGB). If images are
1223 too contrasty or washed out you got the value wrong - check your system
1226 Many systems permit the system gamma to be changed via a lookup table in the
1227 display driver, a few systems, including older Macs, change the response by
1228 default. As of 1.5.4 three special values are available to handle common
1231 PNG_DEFAULT_sRGB: Indicates that the system conforms to the
1232 IEC 61966-2-1 standard. This matches almost
1234 PNG_GAMMA_MAC_18: Indicates that the system is an older
1235 (pre Mac OS 10.6) Apple Macintosh system with
1236 the default settings.
1237 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
1238 that the system expects data with no gamma
1241 You would use the linear (unencoded) value if you need to process the pixel
1242 values further because this avoids the need to decode and reencode each
1243 component value whenever arithmetic is performed. A lot of graphics software
1244 uses linear values for this reason, often with higher precision component values
1245 to preserve overall accuracy.
1247 The second thing you may need to tell libpng about is how your system handles
1248 alpha channel information. Some, but not all, PNG files contain an alpha
1249 channel. To display these files correctly you need to compose the data onto a
1250 suitable background, as described in the PNG specification.
1252 Libpng only supports composing onto a single color (using png_set_background;
1253 see below). Otherwise you must do the composition yourself and, in this case,
1254 you may need to call png_set_alpha_mode:
1256 #if PNG_LIBPNG_VER >= 10504
1257 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1259 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1262 The screen_gamma value is the same as the argument to png_set_gamma; however,
1263 how it affects the output depends on the mode. png_set_alpha_mode() sets the
1264 file gamma default to 1/screen_gamma, so normally you don't need to call
1265 png_set_gamma. If you need different defaults call png_set_gamma() before
1266 png_set_alpha_mode() - if you call it after it will override the settings made
1267 by png_set_alpha_mode().
1269 The mode is as follows:
1271 PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
1272 green and blue, or gray, components are gamma encoded color
1273 values and are not premultiplied by the alpha value. The
1274 alpha value is a linear measure of the contribution of the
1275 pixel to the corresponding final output pixel.
1277 You should normally use this format if you intend to perform
1278 color correction on the color values; most, maybe all, color
1279 correction software has no handling for the alpha channel and,
1280 anyway, the math to handle pre-multiplied component values is
1281 unnecessarily complex.
1283 Before you do any arithmetic on the component values you need
1284 to remove the gamma encoding and multiply out the alpha
1285 channel. See the PNG specification for more detail. It is
1286 important to note that when an image with an alpha channel is
1287 scaled, linear encoded, pre-multiplied component values must
1290 The remaining modes assume you don't need to do any further color correction or
1291 that if you do, your color correction software knows all about alpha (it
1294 PNG_ALPHA_STANDARD: The data libpng produces
1295 is encoded in the standard way
1296 assumed by most correctly written graphics software.
1297 The gamma encoding will be removed by libpng and the
1298 linear component values will be pre-multiplied by the
1301 With this format the final image must be re-encoded to
1302 match the display gamma before the image is displayed.
1303 If your system doesn't do that, yet still seems to
1304 perform arithmetic on the pixels without decoding them,
1305 it is broken - check out the modes below.
1307 With PNG_ALPHA_STANDARD libpng always produces linear
1308 component values, whatever screen_gamma you supply. The
1309 screen_gamma value is, however, used as a default for
1310 the file gamma if the PNG file has no gamma information.
1312 If you call png_set_gamma() after png_set_alpha_mode() you
1313 will override the linear encoding. Instead the
1314 pre-multiplied pixel values will be gamma encoded but
1315 the alpha channel will still be linear. This may
1316 actually match the requirements of some broken software,
1319 While linear 8-bit data is often used it has
1320 insufficient precision for any image with a reasonable
1321 dynamic range. To avoid problems, and if your software
1322 supports it, use png_set_expand_16() to force all
1323 components to 16 bits.
1325 PNG_ALPHA_OPTIMIZED: This mode is the same
1326 as PNG_ALPHA_STANDARD except that
1327 completely opaque pixels are gamma encoded according to
1328 the screen_gamma value. Pixels with alpha less than 1.0
1329 will still have linear components.
1331 Use this format if you have control over your
1332 compositing software and so don't do other arithmetic
1333 (such as scaling) on the data you get from libpng. Your
1334 compositing software can simply copy opaque pixels to
1335 the output but still has linear values for the
1338 In normal compositing, where the alpha channel encodes
1339 partial pixel coverage (as opposed to broad area
1340 translucency), the inaccuracies of the 8-bit
1341 representation of non-opaque pixels are irrelevant.
1343 You can also try this format if your software is broken;
1344 it might look better.
1346 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
1347 however, all component values,
1348 including the alpha channel are gamma encoded. This is
1349 an appropriate format to try if your software, or more
1350 likely hardware, is totally broken, i.e., if it performs
1351 linear arithmetic directly on gamma encoded values.
1353 In most cases of broken software or hardware the bug in the final display
1354 manifests as a subtle halo around composited parts of the image. You may not
1355 even perceive this as a halo; the composited part of the image may simply appear
1356 separate from the background, as though it had been cut out of paper and pasted
1359 If you don't have to deal with bugs in software or hardware, or if you can fix
1360 them, there are three recommended ways of using png_set_alpha_mode():
1362 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1365 You can do color correction on the result (libpng does not currently
1366 support color correction internally). When you handle the alpha channel
1367 you need to undo the gamma encoding and multiply out the alpha.
1369 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1371 png_set_expand_16(png_ptr);
1373 If you are using the high level interface, don't call png_set_expand_16();
1374 instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1376 With this mode you can't do color correction, but you can do arithmetic,
1377 including composition and scaling, on the data without further processing.
1379 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1382 You can avoid the expansion to 16-bit components with this mode, but you
1383 lose the ability to scale the image or perform other linear arithmetic.
1384 All you can do is compose the result onto a matching output. Since this
1385 mode is libpng-specific you also need to write your own composition
1388 If you don't need, or can't handle, the alpha channel you can call
1389 png_set_background() to remove it by compositing against a fixed color. Don't
1390 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1391 transparent parts of this image.
1393 png_set_background(png_ptr, &background_color,
1394 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1396 The background_color is an RGB or grayscale value according to the data format
1397 libpng will produce for you. Because you don't yet know the format of the PNG
1398 file, if you call png_set_background at this point you must arrange for the
1399 format produced by libpng to always have 8-bit or 16-bit components and then
1400 store the color as an 8-bit or 16-bit color as appropriate. The color contains
1401 separate gray and RGB component values, so you can let libpng produce gray or
1402 RGB output according to the input format, but low bit depth grayscale images
1403 must always be converted to at least 8-bit format. (Even though low bit depth
1404 grayscale images can't have an alpha channel they can have a transparent
1407 You set the transforms you need later, either as flags to the high level
1408 interface or libpng API calls for the low level interface. For reference the
1409 settings and API calls required are:
1412 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1413 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1415 If you must get exactly the same inaccurate results
1416 produced by default in versions prior to libpng-1.5.4,
1417 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1421 PNG_TRANSFORM_EXPAND_16
1422 png_set_expand_16(png_ptr);
1424 In either case palette image data will be expanded to RGB. If you just want
1425 color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1428 Calling png_set_background before the PNG file header is read will not work
1429 prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1430 errors it is therefore much safer to call png_set_background after the head has
1431 been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1432 used with the high level interface.
1434 .SS The high-level read interface
1436 At this point there are two ways to proceed; through the high-level
1437 read interface, or through a sequence of low-level read operations.
1438 You can use the high-level interface if (a) you are willing to read
1439 the entire image into memory, and (b) the input transformations
1440 you want to do are limited to the following set:
1442 PNG_TRANSFORM_IDENTITY No transformation
1443 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1445 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1446 8-bit less accurately
1447 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1448 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1450 PNG_TRANSFORM_PACKSWAP Change order of packed
1452 PNG_TRANSFORM_EXPAND Perform set_expand()
1453 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1454 PNG_TRANSFORM_SHIFT Normalize pixels to the
1456 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1458 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1460 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1462 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1463 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1464 to RGB (or GA to RGBA)
1465 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1467 (This excludes setting a background color, doing gamma transformation,
1468 quantizing, and setting filler.) If this is the case, simply do this:
1470 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1472 where png_transforms is an integer containing the bitwise OR of some
1473 set of transformation flags. This call is equivalent to png_read_info(),
1474 followed the set of transformations indicated by the transform mask,
1475 then png_read_image(), and finally png_read_end().
1477 (The final parameter of this call is not yet used. Someday it might point
1478 to transformation parameters required by some future input transform.)
1480 You must use png_transforms and not call any png_set_transform() functions
1481 when you use png_read_png().
1483 After you have called png_read_png(), you can retrieve the image data
1486 row_pointers = png_get_rows(png_ptr, info_ptr);
1488 where row_pointers is an array of pointers to the pixel data for each row:
1490 png_bytep row_pointers[height];
1492 If you know your image size and pixel size ahead of time, you can allocate
1493 row_pointers prior to calling png_read_png() with
1495 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1497 "Image is too tall to process in memory");
1499 if (width > PNG_UINT_32_MAX/pixel_size)
1501 "Image is too wide to process in memory");
1503 row_pointers = png_malloc(png_ptr,
1504 height*png_sizeof(png_bytep));
1506 for (int i=0; i<height, i++)
1507 row_pointers[i]=NULL; /* security precaution */
1509 for (int i=0; i<height, i++)
1510 row_pointers[i]=png_malloc(png_ptr,
1513 png_set_rows(png_ptr, info_ptr, &row_pointers);
1515 Alternatively you could allocate your image in one big block and define
1516 row_pointers[i] to point into the proper places in your block.
1518 If you use png_set_rows(), the application is responsible for freeing
1519 row_pointers (and row_pointers[i], if they were separately allocated).
1521 If you don't allocate row_pointers ahead of time, png_read_png() will
1522 do it, and it'll be free'ed by libpng when you call png_destroy_*().
1524 .SS The low-level read interface
1526 If you are going the low-level route, you are now ready to read all
1527 the file information up to the actual image data. You do this with a
1528 call to png_read_info().
1530 png_read_info(png_ptr, info_ptr);
1532 This will process all chunks up to but not including the image data.
1534 This also copies some of the data from the PNG file into the decode structure
1535 for use in later transformations. Important information copied in is:
1537 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
1538 provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1540 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1541 damages the information provided by an earlier call to png_set_background
1542 resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1544 3) The number of significant bits in each component value. Libpng uses this to
1545 optimize gamma handling by reducing the internal lookup table sizes.
1547 4) The transparent color information from a tRNS chunk. This can be modified by
1548 a later call to png_set_tRNS.
1550 .SS Querying the info structure
1552 Functions are used to get the information from the info_ptr once it
1553 has been read. Note that these fields may not be completely filled
1554 in until png_read_end() has read the chunk data following the image.
1556 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1557 &bit_depth, &color_type, &interlace_type,
1558 &compression_type, &filter_method);
1560 width - holds the width of the image
1561 in pixels (up to 2^31).
1563 height - holds the height of the image
1564 in pixels (up to 2^31).
1566 bit_depth - holds the bit depth of one of the
1567 image channels. (valid values are
1568 1, 2, 4, 8, 16 and depend also on
1569 the color_type. See also
1570 significant bits (sBIT) below).
1572 color_type - describes which color/alpha channels
1575 (bit depths 1, 2, 4, 8, 16)
1576 PNG_COLOR_TYPE_GRAY_ALPHA
1578 PNG_COLOR_TYPE_PALETTE
1579 (bit depths 1, 2, 4, 8)
1582 PNG_COLOR_TYPE_RGB_ALPHA
1585 PNG_COLOR_MASK_PALETTE
1586 PNG_COLOR_MASK_COLOR
1587 PNG_COLOR_MASK_ALPHA
1589 interlace_type - (PNG_INTERLACE_NONE or
1590 PNG_INTERLACE_ADAM7)
1592 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1595 filter_method - (must be PNG_FILTER_TYPE_BASE
1596 for PNG 1.0, and can also be
1597 PNG_INTRAPIXEL_DIFFERENCING if
1598 the PNG datastream is embedded in
1599 a MNG-1.0 datastream)
1601 Any or all of interlace_type, compression_type, or
1602 filter_method can be NULL if you are
1603 not interested in their values.
1605 Note that png_get_IHDR() returns 32-bit data into
1606 the application's width and height variables.
1607 This is an unsafe situation if these are 16-bit
1608 variables. In such situations, the
1609 png_get_image_width() and png_get_image_height()
1610 functions described below are safer.
1612 width = png_get_image_width(png_ptr,
1615 height = png_get_image_height(png_ptr,
1618 bit_depth = png_get_bit_depth(png_ptr,
1621 color_type = png_get_color_type(png_ptr,
1624 interlace_type = png_get_interlace_type(png_ptr,
1627 compression_type = png_get_compression_type(png_ptr,
1630 filter_method = png_get_filter_type(png_ptr,
1633 channels = png_get_channels(png_ptr, info_ptr);
1635 channels - number of channels of info for the
1636 color type (valid values are 1 (GRAY,
1637 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1638 4 (RGB_ALPHA or RGB + filler byte))
1640 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1642 rowbytes - number of bytes needed to hold a row
1644 signature = png_get_signature(png_ptr, info_ptr);
1646 signature - holds the signature read from the
1647 file (if any). The data is kept in
1648 the same offset it would be if the
1649 whole signature were read (i.e. if an
1650 application had already read in 4
1651 bytes of signature before starting
1652 libpng, the remaining 4 bytes would
1653 be in signature[4] through signature[7]
1654 (see png_set_sig_bytes())).
1656 These are also important, but their validity depends on whether the chunk
1657 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1658 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1659 data has been read, or zero if it is missing. The parameters to the
1660 png_get_<chunk> are set directly if they are simple data types, or a
1661 pointer into the info_ptr is returned for any complex types.
1663 The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
1664 is simply returned to give the application information about how the
1665 image was encoded. Libpng itself only does transformations using the file
1666 gamma when combining semitransparent pixels with the background color, and,
1667 since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
1668 within the simplified API. Libpng also uses the file gamma when converting
1669 RGB to gray, beginning with libpng-1.0.5, if the application calls
1670 png_set_rgb_to_gray()).
1672 png_get_PLTE(png_ptr, info_ptr, &palette,
1675 palette - the palette for the file
1676 (array of png_color)
1678 num_palette - number of entries in the palette
1680 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1681 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1683 file_gamma - the gamma at which the file is
1684 written (PNG_INFO_gAMA)
1686 int_file_gamma - 100,000 times the gamma at which the
1689 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
1690 &red_y, &green_x, &green_y, &blue_x, &blue_y)
1691 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
1692 &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
1694 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
1695 &int_white_y, &int_red_x, &int_red_y,
1696 &int_green_x, &int_green_y, &int_blue_x,
1698 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
1699 &int_red_Z, &int_green_X, &int_green_Y,
1700 &int_green_Z, &int_blue_X, &int_blue_Y,
1703 {white,red,green,blue}_{x,y}
1704 A color space encoding specified using the
1705 chromaticities of the end points and the
1706 white point. (PNG_INFO_cHRM)
1708 {red,green,blue}_{X,Y,Z}
1709 A color space encoding specified using the
1710 encoding end points - the CIE tristimulus
1711 specification of the intended color of the red,
1712 green and blue channels in the PNG RGB data.
1713 The white point is simply the sum of the three
1714 end points. (PNG_INFO_cHRM)
1716 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1718 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
1719 The presence of the sRGB chunk
1720 means that the pixel data is in the
1721 sRGB color space. This chunk also
1722 implies specific values of gAMA and
1725 png_get_iCCP(png_ptr, info_ptr, &name,
1726 &compression_type, &profile, &proflen);
1728 name - The profile name.
1730 compression_type - The compression type; always
1731 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1732 You may give NULL to this argument to
1735 profile - International Color Consortium color
1736 profile data. May contain NULs.
1738 proflen - length of profile data in bytes.
1740 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1742 sig_bit - the number of significant bits for
1743 (PNG_INFO_sBIT) each of the gray,
1744 red, green, and blue channels,
1745 whichever are appropriate for the
1746 given color type (png_color_16)
1748 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1749 &num_trans, &trans_color);
1751 trans_alpha - array of alpha (transparency)
1752 entries for palette (PNG_INFO_tRNS)
1754 num_trans - number of transparent entries
1757 trans_color - graylevel or color sample values of
1758 the single transparent color for
1759 non-paletted images (PNG_INFO_tRNS)
1761 png_get_hIST(png_ptr, info_ptr, &hist);
1764 hist - histogram of palette (array of
1767 png_get_tIME(png_ptr, info_ptr, &mod_time);
1769 mod_time - time image was last modified
1772 png_get_bKGD(png_ptr, info_ptr, &background);
1774 background - background color (of type
1775 png_color_16p) (PNG_VALID_bKGD)
1776 valid 16-bit red, green and blue
1777 values, regardless of color_type
1779 num_comments = png_get_text(png_ptr, info_ptr,
1780 &text_ptr, &num_text);
1782 num_comments - number of comments
1784 text_ptr - array of png_text holding image
1787 text_ptr[i].compression - type of compression used
1788 on "text" PNG_TEXT_COMPRESSION_NONE
1789 PNG_TEXT_COMPRESSION_zTXt
1790 PNG_ITXT_COMPRESSION_NONE
1791 PNG_ITXT_COMPRESSION_zTXt
1793 text_ptr[i].key - keyword for comment. Must contain
1796 text_ptr[i].text - text comments for current
1797 keyword. Can be empty.
1799 text_ptr[i].text_length - length of text string,
1800 after decompression, 0 for iTXt
1802 text_ptr[i].itxt_length - length of itxt string,
1803 after decompression, 0 for tEXt/zTXt
1805 text_ptr[i].lang - language of comment (empty
1806 string for unknown).
1808 text_ptr[i].lang_key - keyword in UTF-8
1809 (empty string for unknown).
1811 Note that the itxt_length, lang, and lang_key
1812 members of the text_ptr structure only exist when the
1813 library is built with iTXt chunk support. Prior to
1814 libpng-1.4.0 the library was built by default without
1815 iTXt support. Also note that when iTXt is supported,
1816 they contain NULL pointers when the "compression"
1817 field contains PNG_TEXT_COMPRESSION_NONE or
1818 PNG_TEXT_COMPRESSION_zTXt.
1820 num_text - number of comments (same as
1821 num_comments; you can put NULL here
1822 to avoid the duplication)
1824 Note while png_set_text() will accept text, language,
1825 and translated keywords that can be NULL pointers, the
1826 structure returned by png_get_text will always contain
1827 regular zero-terminated C strings. They might be
1828 empty strings but they will never be NULL pointers.
1830 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1833 num_spalettes - number of sPLT chunks read.
1835 palette_ptr - array of palette structures holding
1836 contents of one or more sPLT chunks
1839 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1842 offset_x - positive offset from the left edge
1843 of the screen (can be negative)
1845 offset_y - positive offset from the top edge
1846 of the screen (can be negative)
1848 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1850 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1853 res_x - pixels/unit physical resolution in
1856 res_y - pixels/unit physical resolution in
1859 unit_type - PNG_RESOLUTION_UNKNOWN,
1860 PNG_RESOLUTION_METER
1862 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1865 unit - physical scale units (an integer)
1867 width - width of a pixel in physical scale units
1869 height - height of a pixel in physical scale units
1870 (width and height are doubles)
1872 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1875 unit - physical scale units (an integer)
1877 width - width of a pixel in physical scale units
1878 (expressed as a string)
1880 height - height of a pixel in physical scale units
1881 (width and height are strings like "2.54")
1883 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1884 info_ptr, &unknowns)
1886 unknowns - array of png_unknown_chunk
1887 structures holding unknown chunks
1889 unknowns[i].name - name of unknown chunk
1891 unknowns[i].data - data of unknown chunk
1893 unknowns[i].size - size of unknown chunk's data
1895 unknowns[i].location - position of chunk in file
1897 The value of "i" corresponds to the order in which the
1898 chunks were read from the PNG file or inserted with the
1899 png_set_unknown_chunks() function.
1901 The value of "location" is a bitwise "or" of
1903 PNG_HAVE_IHDR (0x01)
1904 PNG_HAVE_PLTE (0x02)
1905 PNG_AFTER_IDAT (0x08)
1907 The data from the pHYs chunk can be retrieved in several convenient
1910 res_x = png_get_x_pixels_per_meter(png_ptr,
1913 res_y = png_get_y_pixels_per_meter(png_ptr,
1916 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1919 res_x = png_get_x_pixels_per_inch(png_ptr,
1922 res_y = png_get_y_pixels_per_inch(png_ptr,
1925 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1928 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1931 Each of these returns 0 [signifying "unknown"] if
1932 the data is not present or if res_x is 0;
1933 res_x_and_y is 0 if res_x != res_y
1935 Note that because of the way the resolutions are
1936 stored internally, the inch conversions won't
1937 come out to exactly even number. For example,
1938 72 dpi is stored as 0.28346 pixels/meter, and
1939 when this is retrieved it is 71.9988 dpi, so
1940 be sure to round the returned value appropriately
1941 if you want to display a reasonable-looking result.
1943 The data from the oFFs chunk can be retrieved in several convenient
1946 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1948 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1950 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1952 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1954 Each of these returns 0 [signifying "unknown" if both
1955 x and y are 0] if the data is not present or if the
1956 chunk is present but the unit is the pixel. The
1957 remark about inexact inch conversions applies here
1958 as well, because a value in inches can't always be
1959 converted to microns and back without some loss
1962 For more information, see the
1963 PNG specification for chunk contents. Be careful with trusting
1964 rowbytes, as some of the transformations could increase the space
1965 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1966 See png_read_update_info(), below.
1968 A quick word about text_ptr and num_text. PNG stores comments in
1969 keyword/text pairs, one pair per chunk, with no limit on the number
1970 of text chunks, and a 2^31 byte limit on their size. While there are
1971 suggested keywords, there is no requirement to restrict the use to these
1972 strings. It is strongly suggested that keywords and text be sensible
1973 to humans (that's the point), so don't use abbreviations. Non-printing
1974 symbols are not allowed. See the PNG specification for more details.
1975 There is also no requirement to have text after the keyword.
1977 Keywords should be limited to 79 Latin-1 characters without leading or
1978 trailing spaces, but non-consecutive spaces are allowed within the
1979 keyword. It is possible to have the same keyword any number of times.
1980 The text_ptr is an array of png_text structures, each holding a
1981 pointer to a language string, a pointer to a keyword and a pointer to
1982 a text string. The text string, language code, and translated
1983 keyword may be empty or NULL pointers. The keyword/text
1984 pairs are put into the array in the order that they are received.
1985 However, some or all of the text chunks may be after the image, so, to
1986 make sure you have read all the text chunks, don't mess with these
1987 until after you read the stuff after the image. This will be
1988 mentioned again below in the discussion that goes with png_read_end().
1990 .SS Input transformations
1992 After you've read the header information, you can set up the library
1993 to handle any special transformations of the image data. The various
1994 ways to transform the data will be described in the order that they
1995 should occur. This is important, as some of these change the color
1996 type and/or bit depth of the data, and some others only work on
1997 certain color types and bit depths.
1999 Transformations you request are ignored if they don't have any meaning for a
2000 particular input data format. However some transformations can have an effect
2001 as a result of a previous transformation. If you specify a contradictory set of
2002 transformations, for example both adding and removing the alpha channel, you
2003 cannot predict the final result.
2005 The color used for the transparency values should be supplied in the same
2006 format/depth as the current image data. It is stored in the same format/depth
2007 as the image data in a tRNS chunk, so this is what libpng expects for this data.
2009 The color used for the background value depends on the need_expand argument as
2012 Data will be decoded into the supplied row buffers packed into bytes
2013 unless the library has been told to transform it into another format.
2014 For example, 4 bit/pixel paletted or grayscale data will be returned
2015 2 pixels/byte with the leftmost pixel in the high-order bits of the
2016 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2017 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2018 is called to insert filler bytes, either before or after each RGB triplet.
2019 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2020 byte of the color value first, unless png_set_scale_16() is called to
2021 transform it to regular RGB RGB triplets, or png_set_filler() or
2022 png_set_add alpha() is called to insert filler bytes, either before or
2023 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2024 be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2025 or png_set_scale_16().
2027 The following code transforms grayscale images of less than 8 to 8 bits,
2028 changes paletted images to RGB, and adds a full alpha channel if there is
2029 transparency information in a tRNS chunk. This is most useful on
2030 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2031 viewing application that wishes to treat all images in the same way.
2033 if (color_type == PNG_COLOR_TYPE_PALETTE)
2034 png_set_palette_to_rgb(png_ptr);
2036 if (png_get_valid(png_ptr, info_ptr,
2037 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2039 if (color_type == PNG_COLOR_TYPE_GRAY &&
2040 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2042 The first two functions are actually aliases for png_set_expand(), added
2043 in libpng version 1.0.4, with the function names expanded to improve code
2044 readability. In some future version they may actually do different
2047 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2048 added. It expands the sample depth without changing tRNS to alpha.
2050 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2051 png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2052 Use this when the output color or gray channels are made linear to avoid fairly
2053 severe accuracy loss.
2056 png_set_expand_16(png_ptr);
2058 PNG can have files with 16 bits per channel. If you only can handle
2059 8 bits per channel, this will strip the pixels down to 8-bit.
2061 if (bit_depth == 16)
2062 #if PNG_LIBPNG_VER >= 10504
2063 png_set_scale_16(png_ptr);
2065 png_set_strip_16(png_ptr);
2068 (The more accurate "png_set_scale_16()" API became available in libpng version
2071 If you need to process the alpha channel on the image separately from the image
2072 data (for example if you convert it to a bitmap mask) it is possible to have
2073 libpng strip the channel leaving just RGB or gray data:
2075 if (color_type & PNG_COLOR_MASK_ALPHA)
2076 png_set_strip_alpha(png_ptr);
2078 If you strip the alpha channel you need to find some other way of dealing with
2079 the information. If, instead, you want to convert the image to an opaque
2080 version with no alpha channel use png_set_background; see below.
2082 As of libpng version 1.5.2, almost all useful expansions are supported, the
2083 major ommissions are conversion of grayscale to indexed images (which can be
2084 done trivially in the application) and conversion of indexed to grayscale (which
2085 can be done by a trivial manipulation of the palette.)
2087 In the following table, the 01 means grayscale with depth<8, 31 means
2088 indexed with depth<8, other numerals represent the color type, "T" means
2089 the tRNS chunk is present, A means an alpha channel is present, and O
2090 means tRNS or alpha is present but all pixels in the image are opaque.
2092 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2094 01 - [G] - - - - - - - - - - - - -
2095 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2096 0 1 G + . . G G G G G G B B GB GB
2097 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2098 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2099 2 C P C C C + . . C - - CB CB B B
2100 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2101 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2102 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2103 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2104 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2105 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2106 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2107 6A CA PA CA C C A T tT PA P P C CBA + BA
2108 6O CA PBA CA C C A tT T PA P P CBA C BA +
2111 "+" identifies entries where 'from' and 'to' are the same.
2112 "-" means the transformation is not supported.
2113 "." means nothing is necessary (a tRNS chunk can just be ignored).
2114 "t" means the transformation is obtained by png_set_tRNS.
2115 "A" means the transformation is obtained by png_set_add_alpha().
2116 "X" means the transformation is obtained by png_set_expand().
2117 "1" means the transformation is obtained by
2118 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
2119 if there is no transparency in the original or the final
2121 "C" means the transformation is obtained by png_set_gray_to_rgb().
2122 "G" means the transformation is obtained by png_set_rgb_to_gray().
2123 "P" means the transformation is obtained by
2124 png_set_expand_palette_to_rgb().
2125 "p" means the transformation is obtained by png_set_packing().
2126 "Q" means the transformation is obtained by png_set_quantize().
2127 "T" means the transformation is obtained by
2128 png_set_tRNS_to_alpha().
2129 "B" means the transformation is obtained by
2130 png_set_background(), or png_strip_alpha().
2132 When an entry has multiple transforms listed all are required to cause the
2133 right overall transformation. When two transforms are separated by a comma
2134 either will do the job. When transforms are enclosed in [] the transform should
2135 do the job but this is currently unimplemented - a different format will result
2136 if the suggested transformations are used.
2138 In PNG files, the alpha channel in an image
2139 is the level of opacity. If you need the alpha channel in an image to
2140 be the level of transparency instead of opacity, you can invert the
2141 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2142 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2143 images) is fully transparent, with
2145 png_set_invert_alpha(png_ptr);
2147 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2148 they can, resulting in, for example, 8 pixels per byte for 1 bit
2149 files. This code expands to 1 pixel per byte without changing the
2150 values of the pixels:
2153 png_set_packing(png_ptr);
2155 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2156 stored in a PNG image have been "scaled" or "shifted" up to the next
2157 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2158 to 8 bits/sample in the range [0, 255]). However, it is also possible
2159 to convert the PNG pixel data back to the original bit depth of the
2160 image. This call reduces the pixels back down to the original bit depth:
2162 png_color_8p sig_bit;
2164 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2165 png_set_shift(png_ptr, sig_bit);
2167 PNG files store 3-color pixels in red, green, blue order. This code
2168 changes the storage of the pixels to blue, green, red:
2170 if (color_type == PNG_COLOR_TYPE_RGB ||
2171 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2172 png_set_bgr(png_ptr);
2174 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2175 into 4 or 8 bytes for windowing systems that need them in this format:
2177 if (color_type == PNG_COLOR_TYPE_RGB)
2178 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2180 where "filler" is the 8 or 16-bit number to fill with, and the location is
2181 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2182 you want the filler before the RGB or after. This transformation
2183 does not affect images that already have full alpha channels. To add an
2184 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2185 will generate RGBA pixels.
2187 Note that png_set_filler() does not change the color type. If you want
2188 to do that, you can add a true alpha channel with
2190 if (color_type == PNG_COLOR_TYPE_RGB ||
2191 color_type == PNG_COLOR_TYPE_GRAY)
2192 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2194 where "filler" contains the alpha value to assign to each pixel.
2195 This function was added in libpng-1.2.7.
2197 If you are reading an image with an alpha channel, and you need the
2198 data as ARGB instead of the normal PNG format RGBA:
2200 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2201 png_set_swap_alpha(png_ptr);
2203 For some uses, you may want a grayscale image to be represented as
2204 RGB. This code will do that conversion:
2206 if (color_type == PNG_COLOR_TYPE_GRAY ||
2207 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2208 png_set_gray_to_rgb(png_ptr);
2210 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2213 if (color_type == PNG_COLOR_TYPE_RGB ||
2214 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2215 png_set_rgb_to_gray(png_ptr, error_action,
2216 double red_weight, double green_weight);
2218 error_action = 1: silently do the conversion
2220 error_action = 2: issue a warning if the original
2221 image has any pixel where
2222 red != green or red != blue
2224 error_action = 3: issue an error and abort the
2225 conversion if the original
2226 image has any pixel where
2227 red != green or red != blue
2229 red_weight: weight of red component
2231 green_weight: weight of green component
2232 If either weight is negative, default
2235 In the corresponding fixed point API the red_weight and green_weight values are
2236 simply scaled by 100,000:
2238 png_set_rgb_to_gray(png_ptr, error_action,
2239 png_fixed_point red_weight,
2240 png_fixed_point green_weight);
2242 If you have set error_action = 1 or 2, you can
2243 later check whether the image really was gray, after processing
2244 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2245 It will return a png_byte that is zero if the image was gray or
2246 1 if there were any non-gray pixels. Background and sBIT data
2247 will be silently converted to grayscale, using the green channel
2248 data for sBIT, regardless of the error_action setting.
2250 The default values come from the PNG file cHRM chunk if present; otherwise, the
2251 defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2252 space, as recommended in the Charles Poynton's Colour FAQ,
2253 <http://www.poynton.com/>, in section 9:
2255 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2257 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2259 Previous versions of this document, 1998 through 2002, recommended a slightly
2262 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2264 Libpng uses an integer approximation:
2266 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2268 The calculation is done in a linear colorspace, if the image gamma
2271 The png_set_background() function has been described already; it tells libpng to
2272 composite images with alpha or simple transparency against the supplied
2273 background color. For compatibility with versions of libpng earlier than
2274 libpng-1.5.4 it is recommended that you call the function after reading the file
2275 header, even if you don't want to use the color in a bKGD chunk, if one exists.
2277 If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2278 you may use this color, or supply another color more suitable for
2279 the current display (e.g., the background color from a web page). You
2280 need to tell libpng how the color is represented, both the format of the
2281 component values in the color (the number of bits) and the gamma encoding of the
2282 color. The function takes two arguments, background_gamma_mode and need_expand
2283 to convey this information; however, only two combinations are likely to be
2286 png_color_16 my_background;
2287 png_color_16p image_background;
2289 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2290 png_set_background(png_ptr, image_background,
2291 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2293 png_set_background(png_ptr, &my_background,
2294 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2296 The second call was described above - my_background is in the format of the
2297 final, display, output produced by libpng. Because you now know the format of
2298 the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2299 output and to retain palette images (the palette colors will be modified
2300 appropriately and the tRNS chunk removed.) However, if you are doing this,
2301 take great care not to ask for transformations without checking first that
2304 In the first call the background color has the original bit depth and color type
2305 of the PNG file. So, for palette images the color is supplied as a palette
2306 index and for low bit greyscale images the color is a reduced bit value in
2307 image_background->gray.
2309 If you didn't call png_set_gamma() before reading the file header, for example
2310 if you need your code to remain compatible with older versions of libpng prior
2311 to libpng-1.5.4, this is the place to call it.
2313 Do not call it if you called png_set_alpha_mode(); doing so will damage the
2314 settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2315 supported then you can certainly do png_set_gamma() before reading the PNG
2318 This API unconditionally sets the screen and file gamma values, so it will
2319 override the value in the PNG file unless it is called before the PNG file
2320 reading starts. For this reason you must always call it with the PNG file
2321 value when you call it in this position:
2323 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2324 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2327 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2329 If you need to reduce an RGB file to a paletted file, or if a paletted
2330 file has more entries then will fit on your screen, png_set_quantize()
2331 will do that. Note that this is a simple match quantization that merely
2332 finds the closest color available. This should work fairly well with
2333 optimized palettes, but fairly badly with linear color cubes. If you
2334 pass a palette that is larger than maximum_colors, the file will
2335 reduce the number of colors in the palette so it will fit into
2336 maximum_colors. If there is a histogram, libpng will use it to make
2337 more intelligent choices when reducing the palette. If there is no
2338 histogram, it may not do as good a job.
2340 if (color_type & PNG_COLOR_MASK_COLOR)
2342 if (png_get_valid(png_ptr, info_ptr,
2345 png_uint_16p histogram = NULL;
2347 png_get_hIST(png_ptr, info_ptr,
2349 png_set_quantize(png_ptr, palette, num_palette,
2350 max_screen_colors, histogram, 1);
2355 png_color std_color_cube[MAX_SCREEN_COLORS] =
2358 png_set_quantize(png_ptr, std_color_cube,
2359 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2364 PNG files describe monochrome as black being zero and white being one.
2365 The following code will reverse this (make black be one and white be
2368 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2369 png_set_invert_mono(png_ptr);
2371 This function can also be used to invert grayscale and gray-alpha images:
2373 if (color_type == PNG_COLOR_TYPE_GRAY ||
2374 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2375 png_set_invert_mono(png_ptr);
2377 PNG files store 16-bit pixels in network byte order (big-endian,
2378 ie. most significant bits first). This code changes the storage to the
2379 other way (little-endian, i.e. least significant bits first, the
2380 way PCs store them):
2382 if (bit_depth == 16)
2383 png_set_swap(png_ptr);
2385 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2386 need to change the order the pixels are packed into bytes, you can use:
2389 png_set_packswap(png_ptr);
2391 Finally, you can write your own transformation function if none of
2392 the existing ones meets your needs. This is done by setting a callback
2395 png_set_read_user_transform_fn(png_ptr,
2398 You must supply the function
2400 void read_transform_fn(png_structp png_ptr, png_row_infop
2401 row_info, png_bytep data)
2403 See pngtest.c for a working example. Your function will be called
2404 after all of the other transformations have been processed. Take care with
2405 interlaced images if you do the interlace yourself - the width of the row is the
2406 width in 'row_info', not the overall image width.
2408 If supported, libpng provides two information routines that you can use to find
2409 where you are in processing the image:
2411 png_get_current_pass_number(png_structp png_ptr);
2412 png_get_current_row_number(png_structp png_ptr);
2414 Don't try using these outside a transform callback - firstly they are only
2415 supported if user transforms are supported, secondly they may well return
2416 unexpected results unless the row is actually being processed at the moment they
2420 images the value returned is the row in the input sub-image image. Use
2421 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2422 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2424 The discussion of interlace handling above contains more information on how to
2427 You can also set up a pointer to a user structure for use by your
2428 callback function, and you can inform libpng that your transform
2429 function will change the number of channels or bit depth with the
2432 png_set_user_transform_info(png_ptr, user_ptr,
2433 user_depth, user_channels);
2435 The user's application, not libpng, is responsible for allocating and
2436 freeing any memory required for the user structure.
2438 You can retrieve the pointer via the function
2439 png_get_user_transform_ptr(). For example:
2441 voidp read_user_transform_ptr =
2442 png_get_user_transform_ptr(png_ptr);
2444 The last thing to handle is interlacing; this is covered in detail below,
2445 but you must call the function here if you want libpng to handle expansion
2446 of the interlaced image.
2448 number_of_passes = png_set_interlace_handling(png_ptr);
2450 After setting the transformations, libpng can update your png_info
2451 structure to reflect any transformations you've requested with this
2454 png_read_update_info(png_ptr, info_ptr);
2456 This is most useful to update the info structure's rowbytes
2457 field so you can use it to allocate your image memory. This function
2458 will also update your palette with the correct screen_gamma and
2459 background if these have been given with the calls above. You may
2460 only call png_read_update_info() once with a particular info_ptr.
2462 After you call png_read_update_info(), you can allocate any
2463 memory you need to hold the image. The row data is simply
2464 raw byte data for all forms of images. As the actual allocation
2465 varies among applications, no example will be given. If you
2466 are allocating one large chunk, you will need to build an
2467 array of pointers to each row, as it will be needed for some
2468 of the functions below.
2470 Remember: Before you call png_read_update_info(), the png_get_*()
2471 functions return the values corresponding to the original PNG image.
2472 After you call png_read_update_info the values refer to the image
2473 that libpng will output. Consequently you must call all the png_set_
2474 functions before you call png_read_update_info(). This is particularly
2475 important for png_set_interlace_handling() - if you are going to call
2476 png_read_update_info() you must call png_set_interlace_handling() before
2477 it unless you want to receive interlaced output.
2479 .SS Reading image data
2481 After you've allocated memory, you can read the image data.
2482 The simplest way to do this is in one function call. If you are
2483 allocating enough memory to hold the whole image, you can just
2484 call png_read_image() and libpng will read in all the image data
2485 and put it in the memory area supplied. You will need to pass in
2486 an array of pointers to each row.
2488 This function automatically handles interlacing, so you don't
2489 need to call png_set_interlace_handling() (unless you call
2490 png_read_update_info()) or call this function multiple times, or any
2491 of that other stuff necessary with png_read_rows().
2493 png_read_image(png_ptr, row_pointers);
2495 where row_pointers is:
2497 png_bytep row_pointers[height];
2499 You can point to void or char or whatever you use for pixels.
2501 If you don't want to read in the whole image at once, you can
2502 use png_read_rows() instead. If there is no interlacing (check
2503 interlace_type == PNG_INTERLACE_NONE), this is simple:
2505 png_read_rows(png_ptr, row_pointers, NULL,
2508 where row_pointers is the same as in the png_read_image() call.
2510 If you are doing this just one row at a time, you can do this with
2511 a single row_pointer instead of an array of row_pointers:
2513 png_bytep row_pointer = row;
2514 png_read_row(png_ptr, row_pointer, NULL);
2516 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2517 get somewhat harder. The only current (PNG Specification version 1.2)
2518 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2519 a somewhat complicated 2D interlace scheme, known as Adam7, that
2520 breaks down an image into seven smaller images of varying size, based
2521 on an 8x8 grid. This number is defined (from libpng 1.5) as
2522 PNG_INTERLACE_ADAM7_PASSES in png.h
2524 libpng can fill out those images or it can give them to you "as is".
2525 It is almost always better to have libpng handle the interlacing for you.
2526 If you want the images filled out, there are two ways to do that. The one
2527 mentioned in the PNG specification is to expand each pixel to cover
2528 those pixels that have not been read yet (the "rectangle" method).
2529 This results in a blocky image for the first pass, which gradually
2530 smooths out as more pixels are read. The other method is the "sparkle"
2531 method, where pixels are drawn only in their final locations, with the
2532 rest of the image remaining whatever colors they were initialized to
2533 before the start of the read. The first method usually looks better,
2534 but tends to be slower, as there are more pixels to put in the rows.
2536 If, as is likely, you want libpng to expand the images, call this before
2537 calling png_start_read_image() or png_read_update_info():
2539 if (interlace_type == PNG_INTERLACE_ADAM7)
2541 = png_set_interlace_handling(png_ptr);
2543 This will return the number of passes needed. Currently, this is seven,
2544 but may change if another interlace type is added. This function can be
2545 called even if the file is not interlaced, where it will return one pass.
2546 You then need to read the whole image 'number_of_passes' times. Each time
2547 will distribute the pixels from the current pass to the correct place in
2548 the output image, so you need to supply the same rows to png_read_rows in
2551 If you are not going to display the image after each pass, but are
2552 going to wait until the entire image is read in, use the sparkle
2553 effect. This effect is faster and the end result of either method
2554 is exactly the same. If you are planning on displaying the image
2555 after each pass, the "rectangle" effect is generally considered the
2558 If you only want the "sparkle" effect, just call png_read_rows() as
2559 normal, with the third parameter NULL. Make sure you make pass over
2560 the image number_of_passes times, and you don't change the data in the
2561 rows between calls. You can change the locations of the data, just
2562 not the data. Each pass only writes the pixels appropriate for that
2563 pass, and assumes the data from previous passes is still valid.
2565 png_read_rows(png_ptr, row_pointers, NULL,
2568 If you only want the first effect (the rectangles), do the same as
2569 before except pass the row buffer in the third parameter, and leave
2570 the second parameter NULL.
2572 png_read_rows(png_ptr, NULL, row_pointers,
2575 If you don't want libpng to handle the interlacing details, just call
2576 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2577 Each of the images is a valid image by itself; however, you will almost
2578 certainly need to distribute the pixels from each sub-image to the
2579 correct place. This is where everything gets very tricky.
2581 If you want to retrieve the separate images you must pass the correct
2582 number of rows to each successive call of png_read_rows(). The calculation
2583 gets pretty complicated for small images, where some sub-images may
2584 not even exist because either their width or height ends up zero.
2585 libpng provides two macros to help you in 1.5 and later versions:
2587 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2588 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2590 Respectively these tell you the width and height of the sub-image
2591 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2592 this can be confusing because the specification refers to the same passes
2593 as 1 to 7! Be careful, you must check both the width and height before
2594 calling png_read_rows() and not call it for that pass if either is zero.
2596 You can, of course, read each sub-image row by row. If you want to
2597 produce optimal code to make a pixel-by-pixel transformation of an
2598 interlaced image this is the best approach; read each row of each pass,
2599 transform it, and write it out to a new interlaced image.
2601 If you want to de-interlace the image yourself libpng provides further
2602 macros to help that tell you where to place the pixels in the output image.
2603 Because the interlacing scheme is rectangular - sub-image pixels are always
2604 arranged on a rectangular grid - all you need to know for each pass is the
2605 starting column and row in the output image of the first pixel plus the
2606 spacing between each pixel. As of libpng 1.5 there are four macros to
2607 retrieve this information:
2609 png_uint_32 x = PNG_PASS_START_COL(pass);
2610 png_uint_32 y = PNG_PASS_START_ROW(pass);
2611 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2612 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2614 These allow you to write the obvious loop:
2616 png_uint_32 input_y = 0;
2617 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2619 while (output_y < output_image_height)
2621 png_uint_32 input_x = 0;
2622 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2624 while (output_x < output_image_width)
2626 image[output_y][output_x] =
2627 subimage[pass][input_y][input_x++];
2636 Notice that the steps between successive output rows and columns are
2637 returned as shifts. This is possible because the pixels in the subimages
2638 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2639 image. In practice you may need to directly calculate the output coordinate
2640 given an input coordinate. libpng provides two further macros for this
2643 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2644 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2646 Finally a pair of macros are provided to tell you if a particular image
2647 row or column appears in a given pass:
2649 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2650 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2652 Bear in mind that you will probably also need to check the width and height
2653 of the pass in addition to the above to be sure the pass even exists!
2655 With any luck you are convinced by now that you don't want to do your own
2656 interlace handling. In reality normally the only good reason for doing this
2657 is if you are processing PNG files on a pixel-by-pixel basis and don't want
2658 to load the whole file into memory when it is interlaced.
2660 libpng includes a test program, pngvalid, that illustrates reading and
2661 writing of interlaced images. If you can't get interlacing to work in your
2662 code and don't want to leave it to libpng (the recommended approach), see
2663 how pngvalid.c does it.
2665 .SS Finishing a sequential read
2667 After you are finished reading the image through the
2668 low-level interface, you can finish reading the file. If you are
2669 interested in comments or time, which may be stored either before or
2670 after the image data, you should pass the separate png_info struct if
2671 you want to keep the comments from before and after the image
2674 png_infop end_info = png_create_info_struct(png_ptr);
2678 png_destroy_read_struct(&png_ptr, &info_ptr,
2683 png_read_end(png_ptr, end_info);
2685 If you are not interested, you should still call png_read_end()
2686 but you can pass NULL, avoiding the need to create an end_info structure.
2688 png_read_end(png_ptr, (png_infop)NULL);
2690 If you don't call png_read_end(), then your file pointer will be
2691 left pointing to the first chunk after the last IDAT, which is probably
2692 not what you want if you expect to read something beyond the end of
2695 When you are done, you can free all memory allocated by libpng like this:
2697 png_destroy_read_struct(&png_ptr, &info_ptr,
2700 or, if you didn't create an end_info structure,
2702 png_destroy_read_struct(&png_ptr, &info_ptr,
2705 It is also possible to individually free the info_ptr members that
2706 point to libpng-allocated storage with the following function:
2708 png_free_data(png_ptr, info_ptr, mask, seq)
2710 mask - identifies data to be freed, a mask
2711 containing the bitwise OR of one or
2713 PNG_FREE_PLTE, PNG_FREE_TRNS,
2714 PNG_FREE_HIST, PNG_FREE_ICCP,
2715 PNG_FREE_PCAL, PNG_FREE_ROWS,
2716 PNG_FREE_SCAL, PNG_FREE_SPLT,
2717 PNG_FREE_TEXT, PNG_FREE_UNKN,
2718 or simply PNG_FREE_ALL
2720 seq - sequence number of item to be freed
2723 This function may be safely called when the relevant storage has
2724 already been freed, or has not yet been allocated, or was allocated
2725 by the user and not by libpng, and will in those cases do nothing.
2726 The "seq" parameter is ignored if only one item of the selected data
2727 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
2728 are allowed for the data type identified in the mask, such as text or
2729 sPLT, only the n'th item in the structure is freed, where n is "seq".
2731 The default behavior is only to free data that was allocated internally
2732 by libpng. This can be changed, so that libpng will not free the data,
2733 or so that it will free data that was allocated by the user with png_malloc()
2734 or png_calloc() and passed in via a png_set_*() function, with
2736 png_data_freer(png_ptr, info_ptr, freer, mask)
2739 PNG_DESTROY_WILL_FREE_DATA
2740 PNG_SET_WILL_FREE_DATA
2741 PNG_USER_WILL_FREE_DATA
2743 mask - which data elements are affected
2744 same choices as in png_free_data()
2746 This function only affects data that has already been allocated.
2747 You can call this function after reading the PNG data but before calling
2748 any png_set_*() functions, to control whether the user or the png_set_*()
2749 function is responsible for freeing any existing data that might be present,
2750 and again after the png_set_*() functions to control whether the user
2751 or png_destroy_*() is supposed to free the data. When the user assumes
2752 responsibility for libpng-allocated data, the application must use
2753 png_free() to free it, and when the user transfers responsibility to libpng
2754 for data that the user has allocated, the user must have used png_malloc()
2755 or png_calloc() to allocate it.
2757 If you allocated your row_pointers in a single block, as suggested above in
2758 the description of the high level read interface, you must not transfer
2759 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2760 because they would also try to free the individual row_pointers[i].
2762 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2763 separately, do not transfer responsibility for freeing text_ptr to libpng,
2764 because when libpng fills a png_text structure it combines these members with
2765 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2766 if you transfer responsibility for free'ing text_ptr from libpng to your
2767 application, your application must not separately free those members.
2769 The png_free_data() function will turn off the "valid" flag for anything
2770 it frees. If you need to turn the flag off for a chunk that was freed by
2771 your application instead of by libpng, you can use
2773 png_set_invalid(png_ptr, info_ptr, mask);
2775 mask - identifies the chunks to be made invalid,
2776 containing the bitwise OR of one or
2778 PNG_INFO_gAMA, PNG_INFO_sBIT,
2779 PNG_INFO_cHRM, PNG_INFO_PLTE,
2780 PNG_INFO_tRNS, PNG_INFO_bKGD,
2781 PNG_INFO_hIST, PNG_INFO_pHYs,
2782 PNG_INFO_oFFs, PNG_INFO_tIME,
2783 PNG_INFO_pCAL, PNG_INFO_sRGB,
2784 PNG_INFO_iCCP, PNG_INFO_sPLT,
2785 PNG_INFO_sCAL, PNG_INFO_IDAT
2787 For a more compact example of reading a PNG image, see the file example.c.
2789 .SS Reading PNG files progressively
2791 The progressive reader is slightly different then the non-progressive
2792 reader. Instead of calling png_read_info(), png_read_rows(), and
2793 png_read_end(), you make one call to png_process_data(), which calls
2794 callbacks when it has the info, a row, or the end of the image. You
2795 set up these callbacks with png_set_progressive_read_fn(). You don't
2796 have to worry about the input/output functions of libpng, as you are
2797 giving the library the data directly in png_process_data(). I will
2798 assume that you have read the section on reading PNG files above,
2799 so I will only highlight the differences (although I will show
2802 png_structp png_ptr;
2805 /* An example code fragment of how you would
2806 initialize the progressive reader in your
2809 initialize_png_reader()
2811 png_ptr = png_create_read_struct
2812 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2813 user_error_fn, user_warning_fn);
2818 info_ptr = png_create_info_struct(png_ptr);
2822 png_destroy_read_struct(&png_ptr,
2823 (png_infopp)NULL, (png_infopp)NULL);
2827 if (setjmp(png_jmpbuf(png_ptr)))
2829 png_destroy_read_struct(&png_ptr, &info_ptr,
2834 /* This one's new. You can provide functions
2835 to be called when the header info is valid,
2836 when each row is completed, and when the image
2837 is finished. If you aren't using all functions,
2838 you can specify NULL parameters. Even when all
2839 three functions are NULL, you need to call
2840 png_set_progressive_read_fn(). You can use
2841 any struct as the user_ptr (cast to a void pointer
2842 for the function call), and retrieve the pointer
2843 from inside the callbacks using the function
2845 png_get_progressive_ptr(png_ptr);
2847 which will return a void pointer, which you have
2848 to cast appropriately.
2850 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2851 info_callback, row_callback, end_callback);
2856 /* A code fragment that you call as you receive blocks
2859 process_data(png_bytep buffer, png_uint_32 length)
2861 if (setjmp(png_jmpbuf(png_ptr)))
2863 png_destroy_read_struct(&png_ptr, &info_ptr,
2868 /* This one's new also. Simply give it a chunk
2869 of data from the file stream (in order, of
2870 course). On machines with segmented memory
2871 models machines, don't give it any more than
2872 64K. The library seems to run fine with sizes
2873 of 4K. Although you can give it much less if
2874 necessary (I assume you can give it chunks of
2875 1 byte, I haven't tried less then 256 bytes
2876 yet). When this function returns, you may
2877 want to display any rows that were generated
2878 in the row callback if you don't already do
2881 png_process_data(png_ptr, info_ptr, buffer, length);
2883 /* At this point you can call png_process_data_skip if
2884 you want to handle data the library will skip yourself;
2885 it simply returns the number of bytes to skip (and stops
2886 libpng skipping that number of bytes on the next
2887 png_process_data call).
2891 /* This function is called (as set by
2892 png_set_progressive_read_fn() above) when enough data
2893 has been supplied so all of the header has been
2897 info_callback(png_structp png_ptr, png_infop info)
2899 /* Do any setup here, including setting any of
2900 the transformations mentioned in the Reading
2901 PNG files section. For now, you _must_ call
2902 either png_start_read_image() or
2903 png_read_update_info() after all the
2904 transformations are set (even if you don't set
2905 any). You may start getting rows before
2906 png_process_data() returns, so this is your
2907 last chance to prepare for that.
2909 This is where you turn on interlace handling,
2910 assuming you don't want to do it yourself.
2912 If you need to you can stop the processing of
2913 your original input data at this point by calling
2914 png_process_data_pause. This returns the number
2915 of unprocessed bytes from the last png_process_data
2916 call - it is up to you to ensure that the next call
2917 sees these bytes again. If you don't want to bother
2918 with this you can get libpng to cache the unread
2919 bytes by setting the 'save' parameter (see png.h) but
2920 then libpng will have to copy the data internally.
2924 /* This function is called when each row of image
2927 row_callback(png_structp png_ptr, png_bytep new_row,
2928 png_uint_32 row_num, int pass)
2930 /* If the image is interlaced, and you turned
2931 on the interlace handler, this function will
2932 be called for every row in every pass. Some
2933 of these rows will not be changed from the
2934 previous pass. When the row is not changed,
2935 the new_row variable will be NULL. The rows
2936 and passes are called in order, so you don't
2937 really need the row_num and pass, but I'm
2938 supplying them because it may make your life
2941 If you did not turn on interlace handling then
2942 the callback is called for each row of each
2943 sub-image when the image is interlaced. In this
2944 case 'row_num' is the row in the sub-image, not
2945 the row in the output image as it is in all other
2948 For the non-NULL rows of interlaced images when
2949 you have switched on libpng interlace handling,
2950 you must call png_progressive_combine_row()
2951 passing in the row and the old row. You can
2952 call this function for NULL rows (it will just
2953 return) and for non-interlaced images (it just
2954 does the memcpy for you) if it will make the
2955 code easier. Thus, you can just do this for
2956 all cases if you switch on interlace handling;
2959 png_progressive_combine_row(png_ptr, old_row,
2962 /* where old_row is what was displayed for
2963 previously for the row. Note that the first
2964 pass (pass == 0, really) will completely cover
2965 the old row, so the rows do not have to be
2966 initialized. After the first pass (and only
2967 for interlaced images), you will have to pass
2968 the current row, and the function will combine
2969 the old row and the new row.
2971 You can also call png_process_data_pause in this
2972 callback - see above.
2977 end_callback(png_structp png_ptr, png_infop info)
2979 /* This function is called after the whole image
2980 has been read, including any chunks after the
2981 image (up to and including the IEND). You
2982 will usually have the same info chunk as you
2983 had in the header, although some data may have
2984 been added to the comments and time fields.
2986 Most people won't do much here, perhaps setting
2987 a flag that marks the image as finished.
2995 Much of this is very similar to reading. However, everything of
2996 importance is repeated here, so you won't have to constantly look
2997 back up in the reading section to understand writing.
3001 You will want to do the I/O initialization before you get into libpng,
3002 so if it doesn't work, you don't have anything to undo. If you are not
3003 using the standard I/O functions, you will need to replace them with
3004 custom writing functions. See the discussion under Customizing libpng.
3006 FILE *fp = fopen(file_name, "wb");
3011 Next, png_struct and png_info need to be allocated and initialized.
3012 As these can be both relatively large, you may not want to store these
3013 on the stack, unless you have stack space to spare. Of course, you
3014 will want to check if they return NULL. If you are also reading,
3015 you won't want to name your read structure and your write structure
3016 both "png_ptr"; you can call them anything you like, such as
3017 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
3019 png_structp png_ptr = png_create_write_struct
3020 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3021 user_error_fn, user_warning_fn);
3026 png_infop info_ptr = png_create_info_struct(png_ptr);
3029 png_destroy_write_struct(&png_ptr,
3034 If you want to use your own memory allocation routines,
3035 define PNG_USER_MEM_SUPPORTED and use
3036 png_create_write_struct_2() instead of png_create_write_struct():
3038 png_structp png_ptr = png_create_write_struct_2
3039 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3040 user_error_fn, user_warning_fn, (png_voidp)
3041 user_mem_ptr, user_malloc_fn, user_free_fn);
3043 After you have these structures, you will need to set up the
3044 error handling. When libpng encounters an error, it expects to
3045 longjmp() back to your routine. Therefore, you will need to call
3046 setjmp() and pass the png_jmpbuf(png_ptr). If you
3047 write the file from different routines, you will need to update
3048 the png_jmpbuf(png_ptr) every time you enter a new routine that will
3049 call a png_*() function. See your documentation of setjmp/longjmp
3050 for your compiler for more information on setjmp/longjmp. See
3051 the discussion on libpng error handling in the Customizing Libpng
3052 section below for more information on the libpng error handling.
3054 if (setjmp(png_jmpbuf(png_ptr)))
3056 png_destroy_write_struct(&png_ptr, &info_ptr);
3063 If you would rather avoid the complexity of setjmp/longjmp issues,
3064 you can compile libpng with PNG_NO_SETJMP, in which case
3065 errors will result in a call to PNG_ABORT() which defaults to abort().
3067 You can #define PNG_ABORT() to a function that does something
3068 more useful than abort(), as long as your function does not
3071 Checking for invalid palette index on write was added at libpng
3072 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
3073 a benign error. This is enabled by default because this condition is an
3074 error according to the PNG specification, Clause 11.3.2, but the error can
3075 be ignored in each png_ptr with
3077 png_set_check_for_invalid_index(png_ptr, 0);
3079 If the error is ignored, or if png_benign_error() treats it as a warning,
3080 any invalid pixels are written as-is by the encoder, resulting in an
3081 invalid PNG datastream as output. In this case the application is
3082 responsible for ensuring that the pixel indexes are in range when it writes
3083 a PLTE chunk with fewer entries than the bit depth would allow.
3085 Now you need to set up the output code. The default for libpng is to
3086 use the C function fwrite(). If you use this, you will need to pass a
3087 valid FILE * in the function png_init_io(). Be sure that the file is
3088 opened in binary mode. Again, if you wish to handle writing data in
3089 another way, see the discussion on libpng I/O handling in the Customizing
3090 Libpng section below.
3092 png_init_io(png_ptr, fp);
3094 If you are embedding your PNG into a datastream such as MNG, and don't
3095 want libpng to write the 8-byte signature, or if you have already
3096 written the signature in your application, use
3098 png_set_sig_bytes(png_ptr, 8);
3100 to inform libpng that it should not write a signature.
3104 At this point, you can set up a callback function that will be
3105 called after each row has been written, which you can use to control
3106 a progress meter or the like. It's demonstrated in pngtest.c.
3107 You must supply a function
3109 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3112 /* put your code here */
3115 (You can give it another name that you like instead of "write_row_callback")
3117 To inform libpng about your function, use
3119 png_set_write_status_fn(png_ptr, write_row_callback);
3121 When this function is called the row has already been completely processed and
3122 it has also been written out. The 'row' and 'pass' refer to the next row to be
3124 non-interlaced case the row that was just handled is simply one less than the
3125 passed in row number, and pass will always be 0. For the interlaced case the
3126 same applies unless the row value is 0, in which case the row just handled was
3127 the last one from one of the preceding passes. Because interlacing may skip a
3128 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3129 need to know what the last pass is record (row,pass) from the callback and use
3130 the last recorded value each time.
3132 As with the user transform you can find the output row using the
3133 PNG_ROW_FROM_PASS_ROW macro.
3135 You now have the option of modifying how the compression library will
3136 run. The following functions are mainly for testing, but may be useful
3137 in some cases, like if you need to write PNG files extremely fast and
3138 are willing to give up some compression, or if you want to get the
3139 maximum possible compression at the expense of slower writing. If you
3140 have no special needs in this area, let the library do what it wants by
3141 not calling this function at all, as it has been tuned to deliver a good
3142 speed/compression ratio. The second parameter to png_set_filter() is
3143 the filter method, for which the only valid values are 0 (as of the
3144 July 1999 PNG specification, version 1.2) or 64 (if you are writing
3145 a PNG datastream that is to be embedded in a MNG datastream). The third
3146 parameter is a flag that indicates which filter type(s) are to be tested
3147 for each scanline. See the PNG specification for details on the specific
3151 /* turn on or off filtering, and/or choose
3152 specific filters. You can use either a single
3153 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3154 or more PNG_FILTER_NAME masks.
3156 png_set_filter(png_ptr, 0,
3157 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3158 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3159 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3160 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3161 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3164 If an application wants to start and stop using particular filters during
3165 compression, it should start out with all of the filters (to ensure that
3166 the previous row of pixels will be stored in case it's needed later),
3167 and then add and remove them after the start of compression.
3169 If you are writing a PNG datastream that is to be embedded in a MNG
3170 datastream, the second parameter can be either 0 or 64.
3172 The png_set_compression_*() functions interface to the zlib compression
3173 library, and should mostly be ignored unless you really know what you are
3174 doing. The only generally useful call is png_set_compression_level()
3175 which changes how much time zlib spends on trying to compress the image
3176 data. See the Compression Library (zlib.h and algorithm.txt, distributed
3177 with zlib) for details on the compression levels.
3181 /* Set the zlib compression level */
3182 png_set_compression_level(png_ptr,
3183 Z_BEST_COMPRESSION);
3185 /* Set other zlib parameters for compressing IDAT */
3186 png_set_compression_mem_level(png_ptr, 8);
3187 png_set_compression_strategy(png_ptr,
3188 Z_DEFAULT_STRATEGY);
3189 png_set_compression_window_bits(png_ptr, 15);
3190 png_set_compression_method(png_ptr, 8);
3191 png_set_compression_buffer_size(png_ptr, 8192)
3193 /* Set zlib parameters for text compression
3194 * If you don't call these, the parameters
3195 * fall back on those defined for IDAT chunks
3197 png_set_text_compression_mem_level(png_ptr, 8);
3198 png_set_text_compression_strategy(png_ptr,
3199 Z_DEFAULT_STRATEGY);
3200 png_set_text_compression_window_bits(png_ptr, 15);
3201 png_set_text_compression_method(png_ptr, 8);
3203 .SS Setting the contents of info for output
3205 You now need to fill in the png_info structure with all the data you
3206 wish to write before the actual image. Note that the only thing you
3207 are allowed to write after the image is the text chunks and the time
3208 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3209 the latest PNG specification for more information on that. If you
3210 wish to write them before the image, fill them in now, and flag that
3211 data as being valid. If you want to wait until after the data, don't
3212 fill them until png_write_end(). For all the fields in png_info and
3213 their data types, see png.h. For explanations of what the fields
3214 contain, see the PNG specification.
3216 Some of the more important parts of the png_info are:
3218 png_set_IHDR(png_ptr, info_ptr, width, height,
3219 bit_depth, color_type, interlace_type,
3220 compression_type, filter_method)
3222 width - holds the width of the image
3223 in pixels (up to 2^31).
3225 height - holds the height of the image
3226 in pixels (up to 2^31).
3228 bit_depth - holds the bit depth of one of the
3230 (valid values are 1, 2, 4, 8, 16
3231 and depend also on the
3232 color_type. See also significant
3235 color_type - describes which color/alpha
3236 channels are present.
3238 (bit depths 1, 2, 4, 8, 16)
3239 PNG_COLOR_TYPE_GRAY_ALPHA
3241 PNG_COLOR_TYPE_PALETTE
3242 (bit depths 1, 2, 4, 8)
3245 PNG_COLOR_TYPE_RGB_ALPHA
3248 PNG_COLOR_MASK_PALETTE
3249 PNG_COLOR_MASK_COLOR
3250 PNG_COLOR_MASK_ALPHA
3252 interlace_type - PNG_INTERLACE_NONE or
3255 compression_type - (must be
3256 PNG_COMPRESSION_TYPE_DEFAULT)
3258 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3259 or, if you are writing a PNG to
3260 be embedded in a MNG datastream,
3262 PNG_INTRAPIXEL_DIFFERENCING)
3264 If you call png_set_IHDR(), the call must appear before any of the
3265 other png_set_*() functions, because they might require access to some of
3266 the IHDR settings. The remaining png_set_*() functions can be called
3269 If you wish, you can reset the compression_type, interlace_type, or
3270 filter_method later by calling png_set_IHDR() again; if you do this, the
3271 width, height, bit_depth, and color_type must be the same in each call.
3273 png_set_PLTE(png_ptr, info_ptr, palette,
3276 palette - the palette for the file
3277 (array of png_color)
3278 num_palette - number of entries in the palette
3280 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3281 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3283 file_gamma - the gamma at which the image was
3284 created (PNG_INFO_gAMA)
3286 int_file_gamma - 100,000 times the gamma at which
3287 the image was created
3289 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3290 green_x, green_y, blue_x, blue_y)
3291 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3292 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3293 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3294 int_red_x, int_red_y, int_green_x, int_green_y,
3295 int_blue_x, int_blue_y)
3296 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3297 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3298 int_blue_X, int_blue_Y, int_blue_Z)
3300 {white,red,green,blue}_{x,y}
3301 A color space encoding specified using the chromaticities
3302 of the end points and the white point.
3304 {red,green,blue}_{X,Y,Z}
3305 A color space encoding specified using the encoding end
3306 points - the CIE tristimulus specification of the intended
3307 color of the red, green and blue channels in the PNG RGB
3308 data. The white point is simply the sum of the three end
3311 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3313 srgb_intent - the rendering intent
3314 (PNG_INFO_sRGB) The presence of
3315 the sRGB chunk means that the pixel
3316 data is in the sRGB color space.
3317 This chunk also implies specific
3318 values of gAMA and cHRM. Rendering
3319 intent is the CSS-1 property that
3320 has been defined by the International
3322 (http://www.color.org).
3324 PNG_sRGB_INTENT_SATURATION,
3325 PNG_sRGB_INTENT_PERCEPTUAL,
3326 PNG_sRGB_INTENT_ABSOLUTE, or
3327 PNG_sRGB_INTENT_RELATIVE.
3330 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3333 srgb_intent - the rendering intent
3334 (PNG_INFO_sRGB) The presence of the
3335 sRGB chunk means that the pixel
3336 data is in the sRGB color space.
3337 This function also causes gAMA and
3338 cHRM chunks with the specific values
3339 that are consistent with sRGB to be
3342 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3345 name - The profile name.
3347 compression_type - The compression type; always
3348 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3349 You may give NULL to this argument to
3352 profile - International Color Consortium color
3353 profile data. May contain NULs.
3355 proflen - length of profile data in bytes.
3357 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3359 sig_bit - the number of significant bits for
3360 (PNG_INFO_sBIT) each of the gray, red,
3361 green, and blue channels, whichever are
3362 appropriate for the given color type
3365 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3366 num_trans, trans_color);
3368 trans_alpha - array of alpha (transparency)
3369 entries for palette (PNG_INFO_tRNS)
3371 num_trans - number of transparent entries
3374 trans_color - graylevel or color sample values
3375 (in order red, green, blue) of the
3376 single transparent color for
3377 non-paletted images (PNG_INFO_tRNS)
3379 png_set_hIST(png_ptr, info_ptr, hist);
3381 hist - histogram of palette (array of
3382 png_uint_16) (PNG_INFO_hIST)
3384 png_set_tIME(png_ptr, info_ptr, mod_time);
3386 mod_time - time image was last modified
3389 png_set_bKGD(png_ptr, info_ptr, background);
3391 background - background color (of type
3392 png_color_16p) (PNG_VALID_bKGD)
3394 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3396 text_ptr - array of png_text holding image
3399 text_ptr[i].compression - type of compression used
3400 on "text" PNG_TEXT_COMPRESSION_NONE
3401 PNG_TEXT_COMPRESSION_zTXt
3402 PNG_ITXT_COMPRESSION_NONE
3403 PNG_ITXT_COMPRESSION_zTXt
3404 text_ptr[i].key - keyword for comment. Must contain
3406 text_ptr[i].text - text comments for current
3407 keyword. Can be NULL or empty.
3408 text_ptr[i].text_length - length of text string,
3409 after decompression, 0 for iTXt
3410 text_ptr[i].itxt_length - length of itxt string,
3411 after decompression, 0 for tEXt/zTXt
3412 text_ptr[i].lang - language of comment (NULL or
3414 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3415 or empty for unknown).
3417 Note that the itxt_length, lang, and lang_key
3418 members of the text_ptr structure only exist when the
3419 library is built with iTXt chunk support. Prior to
3420 libpng-1.4.0 the library was built by default without
3421 iTXt support. Also note that when iTXt is supported,
3422 they contain NULL pointers when the "compression"
3423 field contains PNG_TEXT_COMPRESSION_NONE or
3424 PNG_TEXT_COMPRESSION_zTXt.
3426 num_text - number of comments
3428 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3431 palette_ptr - array of png_sPLT_struct structures
3432 to be added to the list of palettes
3433 in the info structure.
3434 num_spalettes - number of palette structures to be
3437 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3440 offset_x - positive offset from the left
3443 offset_y - positive offset from the top
3446 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3448 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3451 res_x - pixels/unit physical resolution
3454 res_y - pixels/unit physical resolution
3457 unit_type - PNG_RESOLUTION_UNKNOWN,
3458 PNG_RESOLUTION_METER
3460 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3462 unit - physical scale units (an integer)
3464 width - width of a pixel in physical scale units
3466 height - height of a pixel in physical scale units
3467 (width and height are doubles)
3469 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3471 unit - physical scale units (an integer)
3473 width - width of a pixel in physical scale units
3474 expressed as a string
3476 height - height of a pixel in physical scale units
3477 (width and height are strings like "2.54")
3479 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3482 unknowns - array of png_unknown_chunk
3483 structures holding unknown chunks
3484 unknowns[i].name - name of unknown chunk
3485 unknowns[i].data - data of unknown chunk
3486 unknowns[i].size - size of unknown chunk's data
3487 unknowns[i].location - position to write chunk in file
3488 0: do not write chunk
3489 PNG_HAVE_IHDR: before PLTE
3490 PNG_HAVE_PLTE: before IDAT
3491 PNG_AFTER_IDAT: after IDAT
3493 The "location" member is set automatically according to
3494 what part of the output file has already been written.
3495 You can change its value after calling png_set_unknown_chunks()
3496 as demonstrated in pngtest.c. Within each of the "locations",
3497 the chunks are sequenced according to their position in the
3498 structure (that is, the value of "i", which is the order in which
3499 the chunk was either read from the input file or defined with
3500 png_set_unknown_chunks).
3502 A quick word about text and num_text. text is an array of png_text
3503 structures. num_text is the number of valid structures in the array.
3504 Each png_text structure holds a language code, a keyword, a text value,
3505 and a compression type.
3507 The compression types have the same valid numbers as the compression
3508 types of the image data. Currently, the only valid number is zero.
3509 However, you can store text either compressed or uncompressed, unlike
3510 images, which always have to be compressed. So if you don't want the
3511 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3512 Because tEXt and zTXt chunks don't have a language field, if you
3513 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3514 any language code or translated keyword will not be written out.
3516 Until text gets around a few hundred bytes, it is not worth compressing it.
3517 After the text has been written out to the file, the compression type
3518 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3519 so that it isn't written out again at the end (in case you are calling
3520 png_write_end() with the same struct).
3522 The keywords that are given in the PNG Specification are:
3524 Title Short (one line) title or
3527 Author Name of image's creator
3529 Description Description of image (possibly long)
3531 Copyright Copyright notice
3533 Creation Time Time of original image creation
3534 (usually RFC 1123 format, see below)
3536 Software Software used to create the image
3538 Disclaimer Legal disclaimer
3540 Warning Warning of nature of content
3542 Source Device used to create the image
3544 Comment Miscellaneous comment; conversion
3545 from other image format
3547 The keyword-text pairs work like this. Keywords should be short
3548 simple descriptions of what the comment is about. Some typical
3549 keywords are found in the PNG specification, as is some recommendations
3550 on keywords. You can repeat keywords in a file. You can even write
3551 some text before the image and some after. For example, you may want
3552 to put a description of the image before the image, but leave the
3553 disclaimer until after, so viewers working over modem connections
3554 don't have to wait for the disclaimer to go over the modem before
3555 they start seeing the image. Finally, keywords should be full
3556 words, not abbreviations. Keywords and text are in the ISO 8859-1
3557 (Latin-1) character set (a superset of regular ASCII) and can not
3558 contain NUL characters, and should not contain control or other
3559 unprintable characters. To make the comments widely readable, stick
3560 with basic ASCII, and avoid machine specific character set extensions
3561 like the IBM-PC character set. The keyword must be present, but
3562 you can leave off the text string on non-compressed pairs.
3563 Compressed pairs must have a text string, as only the text string
3564 is compressed anyway, so the compression would be meaningless.
3566 PNG supports modification time via the png_time structure. Two
3567 conversion routines are provided, png_convert_from_time_t() for
3568 time_t and png_convert_from_struct_tm() for struct tm. The
3569 time_t routine uses gmtime(). You don't have to use either of
3570 these, but if you wish to fill in the png_time structure directly,
3571 you should provide the time in universal time (GMT) if possible
3572 instead of your local time. Note that the year number is the full
3573 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3574 that months start with 1.
3576 If you want to store the time of the original image creation, you should
3577 use a plain tEXt chunk with the "Creation Time" keyword. This is
3578 necessary because the "creation time" of a PNG image is somewhat vague,
3579 depending on whether you mean the PNG file, the time the image was
3580 created in a non-PNG format, a still photo from which the image was
3581 scanned, or possibly the subject matter itself. In order to facilitate
3582 machine-readable dates, it is recommended that the "Creation Time"
3583 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3584 although this isn't a requirement. Unlike the tIME chunk, the
3585 "Creation Time" tEXt chunk is not expected to be automatically changed
3586 by the software. To facilitate the use of RFC 1123 dates, a function
3587 png_convert_to_rfc1123_buffer(png_ptr, buffer, png_timep) is provided to
3588 convert from PNG time to an RFC 1123 format string. The caller must provide
3589 a writeable buffer of at least 29 bytes.
3591 .SS Writing unknown chunks
3593 You can use the png_set_unknown_chunks function to queue up chunks
3594 for writing. You give it a chunk name, raw data, and a size; that's
3595 all there is to it. The chunks will be written by the next following
3596 png_write_info_before_PLTE, png_write_info, or png_write_end function.
3597 Any chunks previously read into the info structure's unknown-chunk
3598 list will also be written out in a sequence that satisfies the PNG
3599 specification's ordering rules.
3601 .SS The high-level write interface
3603 At this point there are two ways to proceed; through the high-level
3604 write interface, or through a sequence of low-level write operations.
3605 You can use the high-level interface if your image data is present
3606 in the info structure. All defined output
3607 transformations are permitted, enabled by the following masks.
3609 PNG_TRANSFORM_IDENTITY No transformation
3610 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3611 PNG_TRANSFORM_PACKSWAP Change order of packed
3613 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3614 PNG_TRANSFORM_SHIFT Normalize pixels to the
3616 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3618 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3620 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3622 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
3623 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3625 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3627 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3630 If you have valid image data in the info structure (you can use
3631 png_set_rows() to put image data in the info structure), simply do this:
3633 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3635 where png_transforms is an integer containing the bitwise OR of some set of
3636 transformation flags. This call is equivalent to png_write_info(),
3637 followed the set of transformations indicated by the transform mask,
3638 then png_write_image(), and finally png_write_end().
3640 (The final parameter of this call is not yet used. Someday it might point
3641 to transformation parameters required by some future output transform.)
3643 You must use png_transforms and not call any png_set_transform() functions
3644 when you use png_write_png().
3646 .SS The low-level write interface
3648 If you are going the low-level route instead, you are now ready to
3649 write all the file information up to the actual image data. You do
3650 this with a call to png_write_info().
3652 png_write_info(png_ptr, info_ptr);
3654 Note that there is one transformation you may need to do before
3655 png_write_info(). In PNG files, the alpha channel in an image is the
3656 level of opacity. If your data is supplied as a level of transparency,
3657 you can invert the alpha channel before you write it, so that 0 is
3658 fully transparent and 255 (in 8-bit or paletted images) or 65535
3659 (in 16-bit images) is fully opaque, with
3661 png_set_invert_alpha(png_ptr);
3663 This must appear before png_write_info() instead of later with the
3664 other transformations because in the case of paletted images the tRNS
3665 chunk data has to be inverted before the tRNS chunk is written. If
3666 your image is not a paletted image, the tRNS data (which in such cases
3667 represents a single color to be rendered as transparent) won't need to
3668 be changed, and you can safely do this transformation after your
3669 png_write_info() call.
3671 If you need to write a private chunk that you want to appear before
3672 the PLTE chunk when PLTE is present, you can write the PNG info in
3673 two steps, and insert code to write your own chunk between them:
3675 png_write_info_before_PLTE(png_ptr, info_ptr);
3676 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3677 png_write_info(png_ptr, info_ptr);
3679 After you've written the file information, you can set up the library
3680 to handle any special transformations of the image data. The various
3681 ways to transform the data will be described in the order that they
3682 should occur. This is important, as some of these change the color
3683 type and/or bit depth of the data, and some others only work on
3684 certain color types and bit depths. Even though each transformation
3685 checks to see if it has data that it can do something with, you should
3686 make sure to only enable a transformation if it will be valid for the
3687 data. For example, don't swap red and blue on grayscale data.
3689 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3690 the library to strip input data that has 4 or 8 bytes per pixel down
3691 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3694 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3696 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3697 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3698 is stored XRGB or RGBX.
3700 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3701 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3702 If the data is supplied at 1 pixel per byte, use this code, which will
3703 correctly pack the pixels into a single byte:
3705 png_set_packing(png_ptr);
3707 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3708 data is of another bit depth, you can write an sBIT chunk into the
3709 file so that decoders can recover the original data if desired.
3711 /* Set the true bit depth of the image data */
3712 if (color_type & PNG_COLOR_MASK_COLOR)
3714 sig_bit.red = true_bit_depth;
3715 sig_bit.green = true_bit_depth;
3716 sig_bit.blue = true_bit_depth;
3721 sig_bit.gray = true_bit_depth;
3724 if (color_type & PNG_COLOR_MASK_ALPHA)
3726 sig_bit.alpha = true_bit_depth;
3729 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3731 If the data is stored in the row buffer in a bit depth other than
3732 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3733 this will scale the values to appear to be the correct bit depth as
3736 png_set_shift(png_ptr, &sig_bit);
3738 PNG files store 16-bit pixels in network byte order (big-endian,
3739 ie. most significant bits first). This code would be used if they are
3740 supplied the other way (little-endian, i.e. least significant bits
3741 first, the way PCs store them):
3744 png_set_swap(png_ptr);
3746 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3747 need to change the order the pixels are packed into bytes, you can use:
3750 png_set_packswap(png_ptr);
3752 PNG files store 3 color pixels in red, green, blue order. This code
3753 would be used if they are supplied as blue, green, red:
3755 png_set_bgr(png_ptr);
3757 PNG files describe monochrome as black being zero and white being
3758 one. This code would be used if the pixels are supplied with this reversed
3759 (black being one and white being zero):
3761 png_set_invert_mono(png_ptr);
3763 Finally, you can write your own transformation function if none of
3764 the existing ones meets your needs. This is done by setting a callback
3767 png_set_write_user_transform_fn(png_ptr,
3768 write_transform_fn);
3770 You must supply the function
3772 void write_transform_fn(png_structp png_ptr, png_row_infop
3773 row_info, png_bytep data)
3775 See pngtest.c for a working example. Your function will be called
3776 before any of the other transformations are processed. If supported
3777 libpng also supplies an information routine that may be called from
3780 png_get_current_row_number(png_ptr);
3781 png_get_current_pass_number(png_ptr);
3783 This returns the current row passed to the transform. With interlaced
3784 images the value returned is the row in the input sub-image image. Use
3785 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
3786 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
3788 The discussion of interlace handling above contains more information on how to
3791 You can also set up a pointer to a user structure for use by your
3794 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3796 The user_channels and user_depth parameters of this function are ignored
3797 when writing; you can set them to zero as shown.
3799 You can retrieve the pointer via the function png_get_user_transform_ptr().
3802 voidp write_user_transform_ptr =
3803 png_get_user_transform_ptr(png_ptr);
3805 It is possible to have libpng flush any pending output, either manually,
3806 or automatically after a certain number of lines have been written. To
3807 flush the output stream a single time call:
3809 png_write_flush(png_ptr);
3811 and to have libpng flush the output stream periodically after a certain
3812 number of scanlines have been written, call:
3814 png_set_flush(png_ptr, nrows);
3816 Note that the distance between rows is from the last time png_write_flush()
3817 was called, or the first row of the image if it has never been called.
3818 So if you write 50 lines, and then png_set_flush 25, it will flush the
3819 output on the next scanline, and every 25 lines thereafter, unless
3820 png_write_flush() is called before 25 more lines have been written.
3821 If nrows is too small (less than about 10 lines for a 640 pixel wide
3822 RGB image) the image compression may decrease noticeably (although this
3823 may be acceptable for real-time applications). Infrequent flushing will
3824 only degrade the compression performance by a few percent over images
3825 that do not use flushing.
3827 .SS Writing the image data
3829 That's it for the transformations. Now you can write the image data.
3830 The simplest way to do this is in one function call. If you have the
3831 whole image in memory, you can just call png_write_image() and libpng
3832 will write the image. You will need to pass in an array of pointers to
3833 each row. This function automatically handles interlacing, so you don't
3834 need to call png_set_interlace_handling() or call this function multiple
3835 times, or any of that other stuff necessary with png_write_rows().
3837 png_write_image(png_ptr, row_pointers);
3839 where row_pointers is:
3841 png_byte *row_pointers[height];
3843 You can point to void or char or whatever you use for pixels.
3845 If you don't want to write the whole image at once, you can
3846 use png_write_rows() instead. If the file is not interlaced,
3849 png_write_rows(png_ptr, row_pointers,
3852 row_pointers is the same as in the png_write_image() call.
3854 If you are just writing one row at a time, you can do this with
3855 a single row_pointer instead of an array of row_pointers:
3857 png_bytep row_pointer = row;
3859 png_write_row(png_ptr, row_pointer);
3861 When the file is interlaced, things can get a good deal more complicated.
3862 The only currently (as of the PNG Specification version 1.2, dated July
3863 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
3864 scheme, that breaks down an image into seven smaller images of varying
3865 size. libpng will build these images for you, or you can do them
3866 yourself. If you want to build them yourself, see the PNG specification
3867 for details of which pixels to write when.
3869 If you don't want libpng to handle the interlacing details, just
3870 use png_set_interlace_handling() and call png_write_rows() the
3871 correct number of times to write all the sub-images
3872 (png_set_interlace_handling() returns the number of sub-images.)
3874 If you want libpng to build the sub-images, call this before you start
3877 number_of_passes = png_set_interlace_handling(png_ptr);
3879 This will return the number of passes needed. Currently, this is seven,
3880 but may change if another interlace type is added.
3882 Then write the complete image number_of_passes times.
3884 png_write_rows(png_ptr, row_pointers, number_of_rows);
3886 Think carefully before you write an interlaced image. Typically code that
3887 reads such images reads all the image data into memory, uncompressed, before
3888 doing any processing. Only code that can display an image on the fly can
3889 take advantage of the interlacing and even then the image has to be exactly
3890 the correct size for the output device, because scaling an image requires
3891 adjacent pixels and these are not available until all the passes have been
3894 If you do write an interlaced image you will hardly ever need to handle
3895 the interlacing yourself. Call png_set_interlace_handling() and use the
3896 approach described above.
3898 The only time it is conceivable that you will really need to write an
3899 interlaced image pass-by-pass is when you have read one pass by pass and
3900 made some pixel-by-pixel transformation to it, as described in the read
3901 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
3902 to determine the size of each sub-image in turn and simply write the rows
3903 you obtained from the read code.
3905 .SS Finishing a sequential write
3907 After you are finished writing the image, you should finish writing
3908 the file. If you are interested in writing comments or time, you should
3909 pass an appropriately filled png_info pointer. If you are not interested,
3912 png_write_end(png_ptr, info_ptr);
3914 When you are done, you can free all memory used by libpng like this:
3916 png_destroy_write_struct(&png_ptr, &info_ptr);
3918 It is also possible to individually free the info_ptr members that
3919 point to libpng-allocated storage with the following function:
3921 png_free_data(png_ptr, info_ptr, mask, seq)
3923 mask - identifies data to be freed, a mask
3924 containing the bitwise OR of one or
3926 PNG_FREE_PLTE, PNG_FREE_TRNS,
3927 PNG_FREE_HIST, PNG_FREE_ICCP,
3928 PNG_FREE_PCAL, PNG_FREE_ROWS,
3929 PNG_FREE_SCAL, PNG_FREE_SPLT,
3930 PNG_FREE_TEXT, PNG_FREE_UNKN,
3931 or simply PNG_FREE_ALL
3933 seq - sequence number of item to be freed
3936 This function may be safely called when the relevant storage has
3937 already been freed, or has not yet been allocated, or was allocated
3938 by the user and not by libpng, and will in those cases do nothing.
3939 The "seq" parameter is ignored if only one item of the selected data
3940 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3941 are allowed for the data type identified in the mask, such as text or
3942 sPLT, only the n'th item in the structure is freed, where n is "seq".
3944 If you allocated data such as a palette that you passed in to libpng
3945 with png_set_*, you must not free it until just before the call to
3946 png_destroy_write_struct().
3948 The default behavior is only to free data that was allocated internally
3949 by libpng. This can be changed, so that libpng will not free the data,
3950 or so that it will free data that was allocated by the user with png_malloc()
3951 or png_calloc() and passed in via a png_set_*() function, with
3953 png_data_freer(png_ptr, info_ptr, freer, mask)
3956 PNG_DESTROY_WILL_FREE_DATA
3957 PNG_SET_WILL_FREE_DATA
3958 PNG_USER_WILL_FREE_DATA
3960 mask - which data elements are affected
3961 same choices as in png_free_data()
3963 For example, to transfer responsibility for some data from a read structure
3964 to a write structure, you could use
3966 png_data_freer(read_ptr, read_info_ptr,
3967 PNG_USER_WILL_FREE_DATA,
3968 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3970 png_data_freer(write_ptr, write_info_ptr,
3971 PNG_DESTROY_WILL_FREE_DATA,
3972 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3974 thereby briefly reassigning responsibility for freeing to the user but
3975 immediately afterwards reassigning it once more to the write_destroy
3976 function. Having done this, it would then be safe to destroy the read
3977 structure and continue to use the PLTE, tRNS, and hIST data in the write
3980 This function only affects data that has already been allocated.
3981 You can call this function before calling after the png_set_*() functions
3982 to control whether the user or png_destroy_*() is supposed to free the data.
3983 When the user assumes responsibility for libpng-allocated data, the
3984 application must use
3985 png_free() to free it, and when the user transfers responsibility to libpng
3986 for data that the user has allocated, the user must have used png_malloc()
3987 or png_calloc() to allocate it.
3989 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3990 separately, do not transfer responsibility for freeing text_ptr to libpng,
3991 because when libpng fills a png_text structure it combines these members with
3992 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3993 if you transfer responsibility for free'ing text_ptr from libpng to your
3994 application, your application must not separately free those members.
3995 For a more compact example of writing a PNG image, see the file example.c.
3997 .SH V. Simplified API
3999 The simplified API, which became available in libpng-1.6.0, hides the details
4000 of both libpng and the PNG file format itself.
4001 It allows PNG files to be read into a very limited number of
4002 in-memory bitmap formats or to be written from the same formats. If these
4003 formats do not accomodate your needs then you can, and should, use the more
4004 sophisticated APIs above - these support a wide variety of in-memory formats
4005 and a wide variety of sophisticated transformations to those formats as well
4006 as a wide variety of APIs to manipulate ancilliary information.
4008 To read a PNG file using the simplified API:
4010 1) Declare a 'png_image' structure (see below) on the
4011 stack and memset() it to all zero.
4013 2) Call the appropriate png_image_begin_read... function.
4015 3) Set the png_image 'format' member to the required
4016 format and allocate a buffer for the image.
4018 4) Call png_image_finish_read to read the image into
4021 There are no restrictions on the format of the PNG input itself; all valid
4022 color types, bit depths, and interlace methods are acceptable, and the
4023 input image is transformed as necessary to the requested in-memory format
4024 during the png_image_finish_read() step.
4026 To write a PNG file using the simplified API:
4028 1) Declare a 'png_image' structure on the stack and memset()
4031 2) Initialize the members of the structure that describe the
4032 image, setting the 'format' member to the format of the
4035 3) Call the appropriate png_image_write... function with a
4036 pointer to the image to write the PNG data.
4038 png_image is a structure that describes the in-memory format of an image
4039 when it is being read or define the in-memory format of an image that you
4040 need to write. The "png_image" structure contains the following members:
4042 png_uint_32 version Set to PNG_IMAGE_VERSION
4043 png_uint_32 width Image width in pixels (columns)
4044 png_uint_32 height Image height in pixels (rows)
4045 png_uint_32 format Image format as defined below
4046 png_uint_32 flags A bit mask containing informational flags
4047 png_controlp opaque Initialize to NULL, free with png_image_free
4048 png_uint_32 colormap_entries; Number of entries in the color-map
4049 png_uint_32 warning_or_error;
4052 In the event of an error or warning the following field warning_or_error
4053 field will be set to a non-zero value and the 'message' field will contain
4054 a '\0' terminated string with the libpng error or warning message. If both
4055 warnings and an error were encountered, only the error is recorded. If there
4056 are multiple warnings, only the first one is recorded.
4058 The upper 30 bits of this value are reserved; the low two bits contain
4059 a two bit code such that a value more than 1 indicates a failure in the API
4062 0 - no warning or error
4065 3 - error preceded by warning
4067 The pixels (samples) of the image have one to four channels whose components
4068 have original values in the range 0 to 1.0:
4070 1: A single gray or luminance channel (G).
4071 2: A gray/luminance channel and an alpha channel (GA).
4072 3: Three red, green, blue color channels (RGB).
4073 4: Three color channels and an alpha channel (RGBA).
4075 The channels are encoded in one of two ways:
4077 a) As a small integer, value 0..255, contained in a single byte. For the
4078 alpha channel the original value is simply value/255. For the color or
4079 luminance channels the value is encoded according to the sRGB specification
4080 and matches the 8-bit format expected by typical display devices.
4082 The color/gray channels are not scaled (pre-multiplied) by the alpha
4083 channel and are suitable for passing to color management software.
4085 b) As a value in the range 0..65535, contained in a 2-byte integer. All
4086 channels can be converted to the original value by dividing by 65535; all
4087 channels are linear. Color channels use the RGB encoding (RGB end-points) of
4088 the sRGB specification. This encoding is identified by the
4089 PNG_FORMAT_FLAG_LINEAR flag below.
4091 When an alpha channel is present it is expected to denote pixel coverage
4092 of the color or luminance channels and is returned as an associated alpha
4093 channel: the color/gray channels are scaled (pre-multiplied) by the alpha
4096 When a color-mapped image is used as a result of calling
4097 png_image_read_colormap or png_image_write_colormap the channels are encoded
4098 in the color-map and the descriptions above apply to the color-map entries.
4099 The image data is encoded as small integers, value 0..255, that index the
4100 entries in the color-map. One integer (one byte) is stored for each pixel.
4104 The #defines to be used in png_image::format. Each #define identifies a
4105 particular layout of channel data and, if present, alpha values. There are
4106 separate defines for each of the two channel encodings.
4108 A format is built up using single bit flag values. Not all combinations are
4109 valid: use the bit flag values below for testing a format returned by the
4110 read APIs, but set formats from the derived values.
4112 When reading or writing color-mapped images the format should be set to the
4113 format of the entries in the color-map then png_image_{read,write}_colormap
4114 called to read or write the color-map and set the format correctly for the
4115 image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
4117 NOTE: libpng can be built with particular features disabled, if you see
4118 compiler errors because the definition of one of the following flags has been
4119 compiled out it is because libpng does not have the required support. It is
4120 possible, however, for the libpng configuration to enable the format on just
4121 read or just write; in that case you may see an error at run time. You can
4122 guard against this by checking for the definition of:
4124 PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
4126 PNG_FORMAT_FLAG_ALPHA 0x01 format with an alpha channel
4127 PNG_FORMAT_FLAG_COLOR 0x02 color format: otherwise grayscale
4128 PNG_FORMAT_FLAG_LINEAR 0x04 png_uint_16 channels else png_byte
4129 PNG_FORMAT_FLAG_COLORMAP 0x08 libpng use only
4130 PNG_FORMAT_FLAG_BGR 0x10 BGR colors, else order is RGB
4131 PNG_FORMAT_FLAG_AFIRST 0x20 alpha channel comes first
4133 Supported formats are as follows. Future versions of libpng may support more
4134 formats; for compatibility with older versions simply check if the format
4135 macro is defined using #ifdef. These defines describe the in-memory layout
4136 of the components of the pixels of the image.
4138 First the single byte formats:
4141 PNG_FORMAT_GA PNG_FORMAT_FLAG_ALPHA
4142 PNG_FORMAT_AG (PNG_FORMAT_GA|PNG_FORMAT_FLAG_AFIRST)
4143 PNG_FORMAT_RGB PNG_FORMAT_FLAG_COLOR
4144 PNG_FORMAT_BGR (PNG_FORMAT_FLAG_COLOR|PNG_FORMAT_FLAG_BGR)
4145 PNG_FORMAT_RGBA (PNG_FORMAT_RGB|PNG_FORMAT_FLAG_ALPHA)
4146 PNG_FORMAT_ARGB (PNG_FORMAT_RGBA|PNG_FORMAT_FLAG_AFIRST)
4147 PNG_FORMAT_BGRA (PNG_FORMAT_BGR|PNG_FORMAT_FLAG_ALPHA)
4148 PNG_FORMAT_ABGR (PNG_FORMAT_BGRA|PNG_FORMAT_FLAG_AFIRST)
4150 Then the linear 2-byte formats. When naming these "Y" is used to
4151 indicate a luminance (gray) channel. The component order within the pixel
4152 is always the same - there is no provision for swapping the order of the
4153 components in the linear format.
4155 PNG_FORMAT_LINEAR_Y PNG_FORMAT_FLAG_LINEAR
4156 PNG_FORMAT_LINEAR_Y_ALPHA
4157 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_ALPHA)
4158 PNG_FORMAT_LINEAR_RGB
4159 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR)
4160 PNG_FORMAT_LINEAR_RGB_ALPHA
4161 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR|
4162 PNG_FORMAT_FLAG_ALPHA)
4164 Color-mapped formats are obtained by calling png_image_{read,write}_colormap,
4165 as appropriate after setting png_image::format to the format of the color-map
4166 to be read or written. Applications may check the value of
4167 PNG_FORMAT_FLAG_COLORMAP to see if they have called the colormap API. The
4168 format of the color-map may be extracted using the following macro.
4170 PNG_FORMAT_OF_COLORMAP(fmt) ((fmt) & ~PNG_FORMAT_FLAG_COLORMAP)
4174 These are convenience macros to derive information from a png_image
4175 structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
4176 actual image sample values - either the entries in the color-map or the
4177 pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
4178 for the pixels and will always return 1 after a call to
4179 png_image_{read,write}_colormap. The remaining macros return information
4180 about the rows in the image and the complete image.
4182 NOTE: All the macros that take a png_image::format parameter are compile time
4183 constants if the format parameter is, itself, a constant. Therefore these
4184 macros can be used in array declarations and case labels where required.
4185 Similarly the macros are also pre-processor constants (sizeof is not used) so
4186 they can be used in #if tests.
4188 First the information about the samples.
4190 PNG_IMAGE_SAMPLE_CHANNELS(fmt)
4191 Returns the total number of channels in a given format: 1..4
4193 PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
4194 Returns the size in bytes of a single component of a pixel or color-map
4195 entry (as appropriate) in the image.
4197 PNG_IMAGE_SAMPLE_SIZE(fmt)
4198 This is the size of the sample data for one sample. If the image is
4199 color-mapped it is the size of one color-map entry (and image pixels are
4200 one byte in size), otherwise it is the size of one image pixel.
4202 PNG_IMAGE_COLORMAP_SIZE(fmt)
4203 The size of the color-map required by the format; this is the size of the
4204 color-map buffer passed to the png_image_{read,write}_colormap APIs, it is
4205 a fixed number determined by the format so can easily be allocated on the
4208 #define PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)\
4209 (PNG_IMAGE_SAMPLE_CHANNELS(fmt) * 256)
4210 /* The maximum size of the color-map required by the format expressed in a
4211 * count of components. This can be used to compile-time allocate a
4214 * png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
4216 * png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
4218 * Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
4219 * information from one of the png_image_begin_read_ APIs and dynamically
4220 * allocate the required memory.
4224 Corresponding information about the pixels
4226 PNG_IMAGE_PIXEL_(test,fmt)
4228 PNG_IMAGE_PIXEL_CHANNELS(fmt)
4229 The number of separate channels (components) in a pixel; 1 for a
4232 PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
4233 The size, in bytes, of each component in a pixel; 1 for a color-mapped
4236 PNG_IMAGE_PIXEL_SIZE(fmt)
4237 The size, in bytes, of a complete pixel; 1 for a color-mapped image.
4239 Information about the whole row, or whole image
4241 PNG_IMAGE_ROW_STRIDE(image)
4242 Returns the total number of components in a single row of the image; this
4243 is the minimum 'row stride', the minimum count of components between each
4244 row. For a color-mapped image this is the minimum number of bytes in a
4247 PNG_IMAGE_BUFFER_SIZE(image, row_stride)
4248 Returns the size, in bytes, of an image buffer given a png_image and a row
4249 stride - the number of components to leave space for in each row.
4251 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
4252 This indicates the the RGB values of the in-memory bitmap do not
4253 correspond to the red, green and blue end-points defined by sRGB.
4255 PNG_IMAGE_FLAG_COLORMAP == 0x02
4256 The PNG is color-mapped. If this flag is set png_image_read_colormap
4257 can be used without further loss of image information. If it is not set
4258 png_image_read_colormap will cause significant loss if the image has any
4262 The png_image passed to the read APIs must have been initialized by setting
4263 the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
4265 int png_image_begin_read_from_file( png_imagep image,
4266 const char *file_name)
4268 The named file is opened for read and the image header
4269 is filled in from the PNG header in the file.
4271 int png_image_begin_read_from_stdio (png_imagep image,
4274 The PNG header is read from the stdio FILE object.
4276 int png_image_begin_read_from_memory(png_imagep image,
4277 png_const_voidp memory, png_size_t size)
4279 The PNG header is read from the given memory buffer.
4281 int png_image_finish_read(png_imagep image,
4282 png_colorp background, void *buffer,
4283 png_int_32 row_stride, void *colormap));
4285 Finish reading the image into the supplied buffer and
4286 clean up the png_image structure.
4288 row_stride is the step, in png_byte or png_uint_16 units
4289 as appropriate, between adjacent rows. A positive stride
4290 indicates that the top-most row is first in the buffer -
4291 the normal top-down arrangement. A negative stride
4292 indicates that the bottom-most row is first in the buffer.
4294 background need only be supplied if an alpha channel must
4295 be removed from a png_byte format and the removal is to be
4296 done by compositing on a solid color; otherwise it may be
4297 NULL and any composition will be done directly onto the
4298 buffer. The value is an sRGB color to use for the
4299 background, for grayscale output the green channel is used.
4301 For linear output removing the alpha channel is always done
4302 by compositing on black.
4304 void png_image_free(png_imagep image)
4306 Free any data allocated by libpng in image->opaque,
4307 setting the pointer to NULL. May be called at any time
4308 after the structure is initialized.
4310 When the simplified API needs to convert between sRGB and linear colorspaces,
4311 the actual sRGB transfer curve defined in the sRGB specification (see the
4312 article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
4313 approximation used elsewhere in libpng.
4317 For write you must initialize a png_image structure to describe the image to
4320 version: must be set to PNG_IMAGE_VERSION
4321 opaque: must be initialized to NULL
4322 width: image width in pixels
4323 height: image height in rows
4324 format: the format of the data you wish to write
4325 flags: set to 0 unless one of the defined flags applies; set
4326 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
4327 where the RGB values do not correspond to the colors in sRGB.
4328 colormap_entries: set to the number of entries in the color-map (0 to 256)
4330 int png_image_write_to_file, (png_imagep image,
4331 const char *file, int convert_to_8bit, const void *buffer,
4332 png_int_32 row_stride, const void *colormap));
4334 Write the image to the named file.
4336 int png_image_write_to_stdio(png_imagep image, FILE *file,
4337 int convert_to_8_bit, const void *buffer,
4338 png_int_32 row_stride, const void *colormap)
4340 Write the image to the given (FILE*).
4342 With all write APIs if image is in one of the linear formats with
4343 (png_uint_16) data then setting convert_to_8_bit will cause the output to be
4344 a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
4345 a 16-bit linear encoded PNG file is written.
4347 With all APIs row_stride is handled as in the read APIs - it is the spacing
4348 from one row to the next in component sized units (float) and if negative
4349 indicates a bottom-up row layout in the buffer.
4351 Note that the write API does not support interlacing, sub-8-bit pixels,
4352 and indexed (paletted) images.
4354 .SH VI. Modifying/Customizing libpng
4356 There are two issues here. The first is changing how libpng does
4357 standard things like memory allocation, input/output, and error handling.
4358 The second deals with more complicated things like adding new chunks,
4359 adding new transformations, and generally changing how libpng works.
4360 Both of those are compile-time issues; that is, they are generally
4361 determined at the time the code is written, and there is rarely a need
4362 to provide the user with a means of changing them.
4364 Memory allocation, input/output, and error handling
4366 All of the memory allocation, input/output, and error handling in libpng
4367 goes through callbacks that are user-settable. The default routines are
4368 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4369 these functions, call the appropriate png_set_*_fn() function.
4371 Memory allocation is done through the functions png_malloc(), png_calloc(),
4372 and png_free(). The png_malloc() and png_free() functions currently just
4373 call the standard C functions and png_calloc() calls png_malloc() and then
4374 clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
4375 is not the same as the calloc(number, size) function provided by stdlib.h.
4376 There is limited support for certain systems with segmented memory
4377 architectures and the types of pointers declared by png.h match this; you
4378 will have to use appropriate pointers in your application. Since it is
4379 unlikely that the method of handling memory allocation on a platform
4380 will change between applications, these functions must be modified in
4381 the library at compile time. If you prefer to use a different method
4382 of allocating and freeing data, you can use png_create_read_struct_2() or
4383 png_create_write_struct_2() to register your own functions as described
4384 above. These functions also provide a void pointer that can be retrieved
4387 mem_ptr=png_get_mem_ptr(png_ptr);
4389 Your replacement memory functions must have prototypes as follows:
4391 png_voidp malloc_fn(png_structp png_ptr,
4392 png_alloc_size_t size);
4394 void free_fn(png_structp png_ptr, png_voidp ptr);
4396 Your malloc_fn() must return NULL in case of failure. The png_malloc()
4397 function will normally call png_error() if it receives a NULL from the
4398 system memory allocator or from your replacement malloc_fn().
4400 Your free_fn() will never be called with a NULL ptr, since libpng's
4401 png_free() checks for NULL before calling free_fn().
4403 Input/Output in libpng is done through png_read() and png_write(),
4404 which currently just call fread() and fwrite(). The FILE * is stored in
4405 png_struct and is initialized via png_init_io(). If you wish to change
4406 the method of I/O, the library supplies callbacks that you can set
4407 through the function png_set_read_fn() and png_set_write_fn() at run
4408 time, instead of calling the png_init_io() function. These functions
4409 also provide a void pointer that can be retrieved via the function
4410 png_get_io_ptr(). For example:
4412 png_set_read_fn(png_structp read_ptr,
4413 voidp read_io_ptr, png_rw_ptr read_data_fn)
4415 png_set_write_fn(png_structp write_ptr,
4416 voidp write_io_ptr, png_rw_ptr write_data_fn,
4417 png_flush_ptr output_flush_fn);
4419 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4420 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4422 The replacement I/O functions must have prototypes as follows:
4424 void user_read_data(png_structp png_ptr,
4425 png_bytep data, png_size_t length);
4427 void user_write_data(png_structp png_ptr,
4428 png_bytep data, png_size_t length);
4430 void user_flush_data(png_structp png_ptr);
4432 The user_read_data() function is responsible for detecting and
4433 handling end-of-data errors.
4435 Supplying NULL for the read, write, or flush functions sets them back
4436 to using the default C stream functions, which expect the io_ptr to
4437 point to a standard *FILE structure. It is probably a mistake
4438 to use NULL for one of write_data_fn and output_flush_fn but not both
4439 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4440 It is an error to read from a write stream, and vice versa.
4442 Error handling in libpng is done through png_error() and png_warning().
4443 Errors handled through png_error() are fatal, meaning that png_error()
4444 should never return to its caller. Currently, this is handled via
4445 setjmp() and longjmp() (unless you have compiled libpng with
4446 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4447 but you could change this to do things like exit() if you should wish,
4448 as long as your function does not return.
4450 On non-fatal errors, png_warning() is called
4451 to print a warning message, and then control returns to the calling code.
4452 By default png_error() and png_warning() print a message on stderr via
4453 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4454 (because you don't want the messages) or PNG_NO_STDIO defined (because
4455 fprintf() isn't available). If you wish to change the behavior of the error
4456 functions, you will need to set up your own message callbacks. These
4457 functions are normally supplied at the time that the png_struct is created.
4458 It is also possible to redirect errors and warnings to your own replacement
4459 functions after png_create_*_struct() has been called by calling:
4461 png_set_error_fn(png_structp png_ptr,
4462 png_voidp error_ptr, png_error_ptr error_fn,
4463 png_error_ptr warning_fn);
4465 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4467 If NULL is supplied for either error_fn or warning_fn, then the libpng
4468 default function will be used, calling fprintf() and/or longjmp() if a
4469 problem is encountered. The replacement error functions should have
4470 parameters as follows:
4472 void user_error_fn(png_structp png_ptr,
4473 png_const_charp error_msg);
4475 void user_warning_fn(png_structp png_ptr,
4476 png_const_charp warning_msg);
4478 The motivation behind using setjmp() and longjmp() is the C++ throw and
4479 catch exception handling methods. This makes the code much easier to write,
4480 as there is no need to check every return code of every function call.
4481 However, there are some uncertainties about the status of local variables
4482 after a longjmp, so the user may want to be careful about doing anything
4483 after setjmp returns non-zero besides returning itself. Consult your
4484 compiler documentation for more details. For an alternative approach, you
4485 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4486 which is illustrated in pngvalid.c and in contrib/visupng.
4488 Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
4489 You can use this to handle certain errors (normally handled as errors)
4492 png_set_benign_errors (png_ptr, int allowed);
4494 allowed: 0: (default) treat png_benign_error() an error.
4495 1: treat png_benign_error() as a warning.
4499 If you need to read or write custom chunks, you may need to get deeper
4500 into the libpng code. The library now has mechanisms for storing
4501 and writing chunks of unknown type; you can even declare callbacks
4502 for custom chunks. However, this may not be good enough if the
4503 library code itself needs to know about interactions between your
4504 chunk and existing `intrinsic' chunks.
4506 If you need to write a new intrinsic chunk, first read the PNG
4507 specification. Acquire a first level of understanding of how it works.
4508 Pay particular attention to the sections that describe chunk names,
4509 and look at how other chunks were designed, so you can do things
4510 similarly. Second, check out the sections of libpng that read and
4511 write chunks. Try to find a chunk that is similar to yours and use
4512 it as a template. More details can be found in the comments inside
4513 the code. It is best to handle private or unknown chunks in a generic method,
4514 via callback functions, instead of by modifying libpng functions. This
4515 is illustrated in pngtest.c, which uses a callback function to handle a
4516 private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4519 If you wish to write your own transformation for the data, look through
4520 the part of the code that does the transformations, and check out some of
4521 the simpler ones to get an idea of how they work. Try to find a similar
4522 transformation to the one you want to add and copy off of it. More details
4523 can be found in the comments inside the code itself.
4525 .SS Configuring for 16-bit platforms
4527 You will want to look into zconf.h to tell zlib (and thus libpng) that
4528 it cannot allocate more then 64K at a time. Even if you can, the memory
4529 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4531 .SS Configuring for DOS
4533 For DOS users who only have access to the lower 640K, you will
4534 have to limit zlib's memory usage via a png_set_compression_mem_level()
4535 call. See zlib.h or zconf.h in the zlib library for more information.
4537 .SS Configuring for Medium Model
4539 Libpng's support for medium model has been tested on most of the popular
4540 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4541 defined, and FAR gets defined to far in pngconf.h, and you should be
4542 all set. Everything in the library (except for zlib's structure) is
4543 expecting far data. You must use the typedefs with the p or pp on
4544 the end for pointers (or at least look at them and be careful). Make
4545 note that the rows of data are defined as png_bytepp, which is
4546 an "unsigned char far * far *".
4548 .SS Configuring for gui/windowing platforms:
4550 You will need to write new error and warning functions that use the GUI
4551 interface, as described previously, and set them to be the error and
4552 warning functions at the time that png_create_*_struct() is called,
4553 in order to have them available during the structure initialization.
4554 They can be changed later via png_set_error_fn(). On some compilers,
4555 you may also have to change the memory allocators (png_malloc, etc.).
4557 .SS Configuring for compiler xxx:
4559 All includes for libpng are in pngconf.h. If you need to add, change
4560 or delete an include, this is the place to do it.
4561 The includes that are not needed outside libpng are placed in pngpriv.h,
4562 which is only used by the routines inside libpng itself.
4563 The files in libpng proper only include pngpriv.h and png.h, which
4564 %14%in turn includes pngconf.h.
4565 in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4566 As of libpng-1.5.0, pngpriv.h also includes three other private header
4567 files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4568 that previously appeared in the public headers.
4570 .SS Configuring zlib:
4572 There are special functions to configure the compression. Perhaps the
4573 most useful one changes the compression level, which currently uses
4574 input compression values in the range 0 - 9. The library normally
4575 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4576 have shown that for a large majority of images, compression values in
4577 the range 3-6 compress nearly as well as higher levels, and do so much
4578 faster. For online applications it may be desirable to have maximum speed
4579 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4580 specify no compression (Z_NO_COMPRESSION = 0), but this would create
4581 files larger than just storing the raw bitmap. You can specify the
4582 compression level by calling:
4585 png_set_compression_level(png_ptr, level);
4587 Another useful one is to reduce the memory level used by the library.
4588 The memory level defaults to 8, but it can be lowered if you are
4589 short on memory (running DOS, for example, where you only have 640K).
4590 Note that the memory level does have an effect on compression; among
4591 other things, lower levels will result in sections of incompressible
4592 data being emitted in smaller stored blocks, with a correspondingly
4593 larger relative overhead of up to 15% in the worst case.
4596 png_set_compression_mem_level(png_ptr, level);
4598 The other functions are for configuring zlib. They are not recommended
4599 for normal use and may result in writing an invalid PNG file. See
4600 zlib.h for more information on what these mean.
4603 png_set_compression_strategy(png_ptr,
4606 png_set_compression_window_bits(png_ptr,
4609 png_set_compression_method(png_ptr, method);
4611 png_set_compression_buffer_size(png_ptr, size);
4613 As of libpng version 1.5.4, additional APIs became
4614 available to set these separately for non-IDAT
4615 compressed chunks such as zTXt, iTXt, and iCCP:
4618 #if PNG_LIBPNG_VER >= 10504
4619 png_set_text_compression_level(png_ptr, level);
4621 png_set_text_compression_mem_level(png_ptr, level);
4623 png_set_text_compression_strategy(png_ptr,
4626 png_set_text_compression_window_bits(png_ptr,
4629 png_set_text_compression_method(png_ptr, method);
4632 .SS Controlling row filtering
4634 If you want to control whether libpng uses filtering or not, which
4635 filters are used, and how it goes about picking row filters, you
4636 can call one of these functions. The selection and configuration
4637 of row filters can have a significant impact on the size and
4638 encoding speed and a somewhat lesser impact on the decoding speed
4639 of an image. Filtering is enabled by default for RGB and grayscale
4640 images (with and without alpha), but not for paletted images nor
4641 for any images with bit depths less than 8 bits/pixel.
4643 The 'method' parameter sets the main filtering method, which is
4644 currently only '0' in the PNG 1.2 specification. The 'filters'
4645 parameter sets which filter(s), if any, should be used for each
4646 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4647 to turn filtering on and off, respectively.
4649 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4650 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4651 ORed together with '|' to specify one or more filters to use.
4652 These filters are described in more detail in the PNG specification.
4653 If you intend to change the filter type during the course of writing
4654 the image, you should start with flags set for all of the filters
4655 you intend to use so that libpng can initialize its internal
4656 structures appropriately for all of the filter types. (Note that this
4657 means the first row must always be adaptively filtered, because libpng
4658 currently does not allocate the filter buffers until png_write_row()
4659 is called for the first time.)
4661 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4662 PNG_FILTER_UP | PNG_FILTER_AVG |
4663 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4665 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4667 The second parameter can also be
4668 PNG_INTRAPIXEL_DIFFERENCING if you are
4669 writing a PNG to be embedded in a MNG
4670 datastream. This parameter must be the
4671 same as the value of filter_method used
4674 It is also possible to influence how libpng chooses from among the
4675 available filters. This is done in one or both of two ways - by
4676 telling it how important it is to keep the same filter for successive
4677 rows, and by telling it the relative computational costs of the filters.
4679 double weights[3] = {1.5, 1.3, 1.1},
4680 costs[PNG_FILTER_VALUE_LAST] =
4681 {1.0, 1.3, 1.3, 1.5, 1.7};
4683 png_set_filter_heuristics(png_ptr,
4684 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4687 The weights are multiplying factors that indicate to libpng that the
4688 row filter should be the same for successive rows unless another row filter
4689 is that many times better than the previous filter. In the above example,
4690 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4691 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
4692 and still be chosen, while the NONE filter could have a sum 1.1 times
4693 higher than other filters and still be chosen. Unspecified weights are
4694 taken to be 1.0, and the specified weights should probably be declining
4695 like those above in order to emphasize recent filters over older filters.
4697 The filter costs specify for each filter type a relative decoding cost
4698 to be considered when selecting row filters. This means that filters
4699 with higher costs are less likely to be chosen over filters with lower
4700 costs, unless their "sum of absolute differences" is that much smaller.
4701 The costs do not necessarily reflect the exact computational speeds of
4702 the various filters, since this would unduly influence the final image
4705 Note that the numbers above were invented purely for this example and
4706 are given only to help explain the function usage. Little testing has
4707 been done to find optimum values for either the costs or the weights.
4709 .SS Removing unwanted object code
4711 There are a bunch of #define's in pngconf.h that control what parts of
4712 libpng are compiled. All the defines end in _SUPPORTED. If you are
4713 never going to use a capability, you can change the #define to #undef
4714 before recompiling libpng and save yourself code and data space, or
4715 you can turn off individual capabilities with defines that begin with
4718 In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4720 You can also turn all of the transforms and ancillary chunk capabilities
4721 off en masse with compiler directives that define
4722 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4724 along with directives to turn on any of the capabilities that you do
4725 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4726 transformations but still leave the library fully capable of reading
4727 and writing PNG files with all known public chunks. Use of the
4728 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4729 that is incapable of reading or writing ancillary chunks. If you are
4730 not using the progressive reading capability, you can turn that off
4731 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4732 capability, which you'll still have).
4734 All the reading and writing specific code are in separate files, so the
4735 linker should only grab the files it needs. However, if you want to
4736 make sure, or if you are building a stand alone library, all the
4737 reading files start with "pngr" and all the writing files start with "pngw".
4738 The files that don't match either (like png.c, pngtrans.c, etc.)
4739 are used for both reading and writing, and always need to be included.
4740 The progressive reader is in pngpread.c
4742 If you are creating or distributing a dynamically linked library (a .so
4743 or DLL file), you should not remove or disable any parts of the library,
4744 as this will cause applications linked with different versions of the
4745 library to fail if they call functions not available in your library.
4746 The size of the library itself should not be an issue, because only
4747 those sections that are actually used will be loaded into memory.
4749 .SS Requesting debug printout
4751 The macro definition PNG_DEBUG can be used to request debugging
4752 printout. Set it to an integer value in the range 0 to 3. Higher
4753 numbers result in increasing amounts of debugging information. The
4754 information is printed to the "stderr" file, unless another file
4755 name is specified in the PNG_DEBUG_FILE macro definition.
4757 When PNG_DEBUG > 0, the following functions (macros) become available:
4759 png_debug(level, message)
4760 png_debug1(level, message, p1)
4761 png_debug2(level, message, p1, p2)
4763 in which "level" is compared to PNG_DEBUG to decide whether to print
4764 the message, "message" is the formatted string to be printed,
4765 and p1 and p2 are parameters that are to be embedded in the string
4766 according to printf-style formatting directives. For example,
4768 png_debug1(2, "foo=%d\n", foo);
4773 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4775 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4776 can still use PNG_DEBUG to control your own debugging:
4782 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4783 having level = 0 will be printed. There aren't any such statements in
4784 this version of libpng, but if you insert some they will be printed.
4786 .SS Prepending a prefix to exported symbols
4788 Starting with libpng-1.6.0, you can configure libpng (when using the
4789 "configure" script) to prefix all exported symbols by means of the
4790 configuration option "--with-libpng-prefix=FOO_", where FOO_ can be any
4791 string beginning with a letter and containing only uppercase
4792 and lowercase letters, digits, and the underscore (i.e., a C language
4793 identifier). This creates a set of macros in pnglibconf.h, so this is
4794 transparent to applications; their function calls get transformed by
4795 the macros to use the modified names.
4797 .SH VII. MNG support
4799 The MNG specification (available at http://www.libpng.org/pub/mng) allows
4800 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4801 Libpng can support some of these extensions. To enable them, use the
4802 png_permit_mng_features() function:
4804 feature_set = png_permit_mng_features(png_ptr, mask)
4806 mask is a png_uint_32 containing the bitwise OR of the
4807 features you want to enable. These include
4808 PNG_FLAG_MNG_EMPTY_PLTE
4809 PNG_FLAG_MNG_FILTER_64
4810 PNG_ALL_MNG_FEATURES
4812 feature_set is a png_uint_32 that is the bitwise AND of
4813 your mask with the set of MNG features that is
4814 supported by the version of libpng that you are using.
4816 It is an error to use this function when reading or writing a standalone
4817 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4818 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4819 and the MHDR and MEND chunks. Libpng does not provide support for these
4820 or any other MNG chunks; your application must provide its own support for
4821 them. You may wish to consider using libmng (available at
4822 http://www.libmng.com) instead.
4824 .SH VIII. Changes to Libpng from version 0.88
4826 It should be noted that versions of libpng later than 0.96 are not
4827 distributed by the original libpng author, Guy Schalnat, nor by
4828 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4829 distributed versions 0.89 through 0.96, but rather by another member
4830 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4831 still alive and well, but they have moved on to other things.
4833 The old libpng functions png_read_init(), png_write_init(),
4834 png_info_init(), png_read_destroy(), and png_write_destroy() have been
4835 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4836 functions will be removed from libpng version 1.4.0.
4838 The preferred method of creating and initializing the libpng structures is
4839 via the png_create_read_struct(), png_create_write_struct(), and
4840 png_create_info_struct() because they isolate the size of the structures
4841 from the application, allow version error checking, and also allow the
4842 use of custom error handling routines during the initialization, which
4843 the old functions do not. The functions png_read_destroy() and
4844 png_write_destroy() do not actually free the memory that libpng
4845 allocated for these structs, but just reset the data structures, so they
4846 can be used instead of png_destroy_read_struct() and
4847 png_destroy_write_struct() if you feel there is too much system overhead
4848 allocating and freeing the png_struct for each image read.
4850 Setting the error callbacks via png_set_message_fn() before
4851 png_read_init() as was suggested in libpng-0.88 is no longer supported
4852 because this caused applications that do not use custom error functions
4853 to fail if the png_ptr was not initialized to zero. It is still possible
4854 to set the error callbacks AFTER png_read_init(), or to change them with
4855 png_set_error_fn(), which is essentially the same function, but with a new
4856 name to force compilation errors with applications that try to use the old
4859 Starting with version 1.0.7, you can find out which version of the library
4860 you are using at run-time:
4862 png_uint_32 libpng_vn = png_access_version_number();
4864 The number libpng_vn is constructed from the major version, minor
4865 version with leading zero, and release number with leading zero,
4866 (e.g., libpng_vn for version 1.0.7 is 10007).
4868 Note that this function does not take a png_ptr, so you can call it
4869 before you've created one.
4871 You can also check which version of png.h you used when compiling your
4874 png_uint_32 application_vn = PNG_LIBPNG_VER;
4876 .SH IX. Changes to Libpng from version 1.0.x to 1.2.x
4878 Support for user memory management was enabled by default. To
4879 accomplish this, the functions png_create_read_struct_2(),
4880 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4881 png_malloc_default(), and png_free_default() were added.
4883 Support for the iTXt chunk has been enabled by default as of
4886 Support for certain MNG features was enabled.
4888 Support for numbered error messages was added. However, we never got
4889 around to actually numbering the error messages. The function
4890 png_set_strip_error_numbers() was added (Note: the prototype for this
4891 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4892 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4894 The png_malloc_warn() function was added at libpng-1.2.3. This issues
4895 a png_warning and returns NULL instead of aborting when it fails to
4896 acquire the requested memory allocation.
4898 Support for setting user limits on image width and height was enabled
4899 by default. The functions png_set_user_limits(), png_get_user_width_max(),
4900 and png_get_user_height_max() were added at libpng-1.2.6.
4902 The png_set_add_alpha() function was added at libpng-1.2.7.
4904 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4905 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4906 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4909 A number of macro definitions in support of runtime selection of
4910 assembler code features (especially Intel MMX code support) were
4911 added at libpng-1.2.0:
4913 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4914 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4915 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4916 PNG_ASM_FLAG_MMX_READ_INTERLACE
4917 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4918 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4919 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4920 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4921 PNG_ASM_FLAGS_INITIALIZED
4927 We added the following functions in support of runtime
4928 selection of assembler code features:
4930 png_get_mmx_flagmask()
4931 png_set_mmx_thresholds()
4933 png_get_mmx_bitdepth_threshold()
4934 png_get_mmx_rowbytes_threshold()
4937 We replaced all of these functions with simple stubs in libpng-1.2.20,
4938 when the Intel assembler code was removed due to a licensing issue.
4940 These macros are deprecated:
4942 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4943 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4944 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4945 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4946 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4947 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4949 They have been replaced, respectively, by:
4951 PNG_NO_READ_TRANSFORMS
4952 PNG_NO_PROGRESSIVE_READ
4953 PNG_NO_SEQUENTIAL_READ
4954 PNG_NO_WRITE_TRANSFORMS
4955 PNG_NO_READ_ANCILLARY_CHUNKS
4956 PNG_NO_WRITE_ANCILLARY_CHUNKS
4958 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4959 deprecated since libpng-1.0.16 and libpng-1.2.6.
4962 png_check_sig(sig, num)
4964 !png_sig_cmp(sig, 0, num)
4965 It has been deprecated since libpng-0.90.
4968 png_set_gray_1_2_4_to_8()
4969 which also expands tRNS to alpha was replaced with
4970 png_set_expand_gray_1_2_4_to_8()
4971 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
4973 .SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
4975 Private libpng prototypes and macro definitions were moved from
4976 png.h and pngconf.h into a new pngpriv.h header file.
4978 Functions png_set_benign_errors(), png_benign_error(), and
4979 png_chunk_benign_error() were added.
4981 Support for setting the maximum amount of memory that the application
4982 will allocate for reading chunks was added, as a security measure.
4983 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
4984 were added to the library.
4986 We implemented support for I/O states by adding png_ptr member io_state
4987 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
4989 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
4992 Checking for and reporting of errors in the IHDR chunk is more thorough.
4994 Support for global arrays was removed, to improve thread safety.
4996 Some obsolete/deprecated macros and functions have been removed.
4998 Typecasted NULL definitions such as
4999 #define png_voidp_NULL (png_voidp)NULL
5000 were eliminated. If you used these in your application, just use
5003 The png_struct and info_struct members "trans" and "trans_values" were
5004 changed to "trans_alpha" and "trans_color", respectively.
5006 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5009 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5011 The PNG_LEGACY_SUPPORTED macro was eliminated.
5013 Many WIN32_WCE #ifdefs were removed.
5015 The functions png_read_init(info_ptr), png_write_init(info_ptr),
5016 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5017 have been removed. They have been deprecated since libpng-0.95.
5019 The png_permit_empty_plte() was removed. It has been deprecated
5020 since libpng-1.0.9. Use png_permit_mng_features() instead.
5022 We removed the obsolete stub functions png_get_mmx_flagmask(),
5023 png_set_mmx_thresholds(), png_get_asm_flags(),
5024 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5025 png_set_asm_flags(), and png_mmx_supported()
5027 We removed the obsolete png_check_sig(), png_memcpy_check(), and
5028 png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5029 and memset(), respectively.
5031 The function png_set_gray_1_2_4_to_8() was removed. It has been
5032 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5033 png_set_expand_gray_1_2_4_to_8() because the former function also
5034 expanded any tRNS chunk to an alpha channel.
5036 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5037 were added and are used by default instead of the corresponding
5038 functions. Unfortunately,
5039 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5040 function) incorrectly returned a value of type png_uint_32.
5042 We changed the prototype for png_malloc() from
5043 png_malloc(png_structp png_ptr, png_uint_32 size)
5045 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5047 This also applies to the prototype for the user replacement malloc_fn().
5049 The png_calloc() function was added and is used in place of
5050 of "png_malloc(); memset();" except in the case in png_read_png()
5051 where the array consists of pointers; in this case a "for" loop is used
5052 after the png_malloc() to set the pointers to NULL, to give robust.
5053 behavior in case the application runs out of memory part-way through
5056 We changed the prototypes of png_get_compression_buffer_size() and
5057 png_set_compression_buffer_size() to work with png_size_t instead of
5060 Support for numbered error messages was removed by default, since we
5061 never got around to actually numbering the error messages. The function
5062 png_set_strip_error_numbers() was removed from the library by default.
5064 The png_zalloc() and png_zfree() functions are no longer exported.
5065 The png_zalloc() function no longer zeroes out the memory that it
5066 allocates. Applications that called png_zalloc(png_ptr, number, size)
5067 can call png_calloc(png_ptr, number*size) instead, and can call
5068 png_free() instead of png_zfree().
5070 Support for dithering was disabled by default in libpng-1.4.0, because
5071 it has not been well tested and doesn't actually "dither".
5073 removed, however, and could be enabled by building libpng with
5074 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5075 was reenabled, but the function was renamed png_set_quantize() to
5076 reflect more accurately what it actually does. At the same time,
5077 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5078 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5079 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5081 We removed the trailing '.' from the warning and error messages.
5083 .SH XI. Changes to Libpng from version 1.4.x to 1.5.x
5085 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5086 function) incorrectly returned a value of type png_uint_32.
5088 Checking for invalid palette index on read or write was added at libpng
5089 1.5.10. When an invalid index is found, libpng issues a benign error.
5090 This is enabled by default because this condition is an error according
5091 to the PNG specification, Clause 11.3.2, but the error can be ignored in
5094 png_set_check_for_invalid_index(png_ptr, allowed);
5097 0: disable benign error (accept the
5098 invalid data without warning).
5099 1: enable benign error (treat the
5100 invalid data as an error or a
5103 If the error is ignored, or if png_benign_error() treats it as a warning,
5104 any invalid pixels are decoded as opaque black by the decoder and written
5105 as-is by the encoder.
5107 Retrieving the maximum palette index found was added at libpng-1.5.15.
5108 This statement must appear after png_read_png() or png_read_image() while
5109 reading, and after png_write_png() or png_write_image() while writing.
5111 int max_palette = png_get_palette_max(png_ptr, info_ptr);
5113 This will return the maximum palette index found in the image, or "-1" if
5114 the palette was not checked, or "0" if no palette was found. Note that this
5115 does not account for any palette index used by ancillary chunks such as the
5116 bKGD chunk; you must check those separately to determine the maximum
5117 palette index actually used.
5119 A. Changes that affect users of libpng
5121 There are no substantial API changes between the non-deprecated parts of
5122 the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
5123 members of the main libpng control structures, png_struct and png_info,
5124 deprecated in earlier versions of libpng, has been completely removed from
5127 We no longer include zlib.h in png.h. The include statement has been moved
5128 to pngstruct.h, where it is not accessible by applications. Applications that
5129 need access to information in zlib.h will need to add the '#include "zlib.h"'
5130 directive. It does not matter whether this is placed prior to or after
5131 the '"#include png.h"' directive.
5133 The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
5136 We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
5137 macros into a private header file (pngpriv.h) that is not accessible to
5140 In png_get_iCCP, the type of "profile" was changed from png_charpp
5141 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5143 There are changes of form in png.h, including new and changed macros to
5144 declare parts of the API. Some API functions with arguments that are
5145 pointers to data not modified within the function have been corrected to
5146 declare these arguments with PNG_CONST.
5148 Much of the internal use of C macros to control the library build has also
5149 changed and some of this is visible in the exported header files, in
5150 particular the use of macros to control data and API elements visible
5151 during application compilation may require significant revision to
5152 application code. (It is extremely rare for an application to do this.)
5154 Any program that compiled against libpng 1.4 and did not use deprecated
5155 features or access internal library structures should compile and work
5156 against libpng 1.5, except for the change in the prototype for
5157 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5159 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5160 interlaced images. The macros return the number of rows and columns in
5161 each pass and information that can be used to de-interlace and (if
5162 absolutely necessary) interlace an image.
5164 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5165 the application-provided png_longjmp_ptr on the internal, but application
5166 initialized, longjmp buffer. It is provided as a convenience to avoid
5167 the need to use the png_jmpbuf macro, which had the unnecessary side
5168 effect of resetting the internal png_longjmp_ptr value.
5170 libpng 1.5.0 includes a complete fixed point API. By default this is
5171 present along with the corresponding floating point API. In general the
5172 fixed point API is faster and smaller than the floating point one because
5173 the PNG file format used fixed point, not floating point. This applies
5174 even if the library uses floating point in internal calculations. A new
5175 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5176 uses floating point arithmetic (the default) or fixed point arithmetic
5177 internally for performance critical calculations such as gamma correction.
5178 In some cases, the gamma calculations may produce slightly different
5179 results. This has changed the results in png_rgb_to_gray and in alpha
5180 composition (png_set_background for example). This applies even if the
5181 original image was already linear (gamma == 1.0) and, therefore, it is
5182 not necessary to linearize the image. This is because libpng has *not*
5183 been changed to optimize that case correctly, yet.
5185 Fixed point support for the sCAL chunk comes with an important caveat;
5186 the sCAL specification uses a decimal encoding of floating point values
5187 and the accuracy of PNG fixed point values is insufficient for
5188 representation of these values. Consequently a "string" API
5189 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5190 arbitrary sCAL chunks in the absence of either the floating point API or
5191 internal floating point calculations.
5193 Applications no longer need to include the optional distribution header
5194 file pngusr.h or define the corresponding macros during application
5195 build in order to see the correct variant of the libpng API. From 1.5.0
5196 application code can check for the corresponding _SUPPORTED macro:
5198 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5199 /* code that uses the inch conversion APIs. */
5202 This macro will only be defined if the inch conversion functions have been
5203 compiled into libpng. The full set of macros, and whether or not support
5204 has been compiled in, are available in the header file pnglibconf.h.
5205 This header file is specific to the libpng build. Notice that prior to
5206 1.5.0 the _SUPPORTED macros would always have the default definition unless
5207 reset by pngusr.h or by explicit settings on the compiler command line.
5208 These settings may produce compiler warnings or errors in 1.5.0 because
5209 of macro redefinition.
5211 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5212 function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
5213 is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
5216 Applications can now choose whether to use these macros or to call the
5217 corresponding function by defining PNG_USE_READ_MACROS or
5218 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5219 only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5220 will lead to a link failure.
5222 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5223 when compressing the IDAT data and textual data such as zTXt and iCCP.
5224 In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5225 We added five png_set_text_*() functions for setting the parameters to
5226 use with textual data.
5228 Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5229 option was off by default, and slightly inaccurate scaling occurred.
5230 This option can no longer be turned off, and the choice of accurate
5231 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5232 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5235 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5236 used to reduce the width and height limits from the value of
5237 PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5238 that it could be used to override them. Now this function will reduce or
5239 increase the limits.
5241 Starting in libpng-1.5.10, the user limits can be set en masse with the
5242 configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
5243 a set of "safe" limits is applied in pngpriv.h. These can be overridden by
5244 application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
5245 and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
5246 in libpng-1.5.10 the default width and height limits were increased
5247 from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
5250 png_user_width_max 0x7fffffff 1,000,000
5251 png_user_height_max 0x7fffffff 1,000,000
5252 png_user_chunk_cache_max 0 (unlimited) 128
5253 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
5255 B. Changes to the build and configuration of libpng
5257 Details of internal changes to the library code can be found in the CHANGES
5258 file and in the GIT repository logs. These will be of no concern to the vast
5259 majority of library users or builders; however, the few who configure libpng
5260 to a non-default feature set may need to change how this is done.
5262 There should be no need for library builders to alter build scripts if
5263 these use the distributed build support - configure or the makefiles -
5264 however, users of the makefiles may care to update their build scripts
5265 to build pnglibconf.h where the corresponding makefile does not do so.
5267 Building libpng with a non-default configuration has changed completely.
5268 The old method using pngusr.h should still work correctly even though the
5269 way pngusr.h is used in the build has been changed; however, library
5270 builders will probably want to examine the changes to take advantage of
5271 new capabilities and to simplify their build system.
5273 B.1 Specific changes to library configuration capabilities
5275 The library now supports a complete fixed point implementation and can
5276 thus be used on systems that have no floating point support or very
5277 limited or slow support. Previously gamma correction, an essential part
5278 of complete PNG support, required reasonably fast floating point.
5280 As part of this the choice of internal implementation has been made
5281 independent of the choice of fixed versus floating point APIs and all the
5282 missing fixed point APIs have been implemented.
5284 The exact mechanism used to control attributes of API functions has
5285 changed. A single set of operating system independent macro definitions
5286 is used and operating system specific directives are defined in
5289 As part of this the mechanism used to choose procedure call standards on
5290 those systems that allow a choice has been changed. At present this only
5291 affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
5292 running on Intel processors. As before, PNGAPI is defined where required
5293 to control the exported API functions; however, two new macros, PNGCBAPI
5294 and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
5295 (PNGCAPI) for functions that must match a C library prototype (currently
5296 only png_longjmp_ptr, which must match the C longjmp function.) The new
5297 approach is documented in pngconf.h
5299 Despite these changes, libpng 1.5.0 only supports the native C function
5300 calling standard on those platforms tested so far (__cdecl on Microsoft
5301 Windows). This is because the support requirements for alternative
5302 calling conventions seem to no longer exist. Developers who find it
5303 necessary to set PNG_API_RULE to 1 should advise the mailing list
5304 (png-mng-implement) of this and library builders who use Openwatcom and
5305 therefore set PNG_API_RULE to 2 should also contact the mailing list.
5307 A new test program, pngvalid, is provided in addition to pngtest.
5308 pngvalid validates the arithmetic accuracy of the gamma correction
5309 calculations and includes a number of validations of the file format.
5310 A subset of the full range of tests is run when "make check" is done
5311 (in the 'configure' build.) pngvalid also allows total allocated memory
5312 usage to be evaluated and performs additional memory overwrite validation.
5314 Many changes to individual feature macros have been made. The following
5315 are the changes most likely to be noticed by library builders who
5318 1) All feature macros now have consistent naming:
5320 #define PNG_NO_feature turns the feature off
5321 #define PNG_feature_SUPPORTED turns the feature on
5323 pnglibconf.h contains one line for each feature macro which is either:
5325 #define PNG_feature_SUPPORTED
5327 if the feature is supported or:
5329 /*#undef PNG_feature_SUPPORTED*/
5331 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5332 It does not, and libpng applications should not, check for the 'NO' macro
5333 which will not normally be defined even if the feature is not supported.
5334 The 'NO' macros are only used internally for setting or not setting the
5335 corresponding 'SUPPORTED' macros.
5337 Compatibility with the old names is provided as follows:
5339 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5341 And the following definitions disable the corresponding feature:
5343 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5344 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5345 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5346 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5347 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5348 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5350 Library builders should remove use of the above, inconsistent, names.
5352 2) Warning and error message formatting was previously conditional on
5353 the STDIO feature. The library has been changed to use the
5354 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5355 the library no longer uses the printf(3) functions, even though the
5356 default read/write implementations use (FILE) style stdio.h functions.
5358 3) Three feature macros now control the fixed/floating point decisions:
5360 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5362 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5363 practice these are normally required internally anyway (because the PNG
5364 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5365 merely stops the function from being exported.
5367 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5368 point implementation or the fixed point one. Typically the fixed point
5369 implementation is larger and slower than the floating point implementation
5370 on a system that supports floating point; however, it may be faster on a
5371 system which lacks floating point hardware and therefore uses a software
5374 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5375 functions to read and write ints to be disabled independently of
5376 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5377 even though the default is to use the macros - this allows applications
5378 to choose at app buildtime whether or not to use macros (previously
5379 impossible because the functions weren't in the default build.)
5381 B.2 Changes to the configuration mechanism
5383 Prior to libpng-1.5.0 library builders who needed to configure libpng
5384 had either to modify the exported pngconf.h header file to add system
5385 specific configuration or had to write feature selection macros into
5386 pngusr.h and cause this to be included into pngconf.h by defining
5387 PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
5388 application built without PNG_USER_CONFIG defined would see the
5389 unmodified, default, libpng API and thus would probably fail to link.
5391 These mechanisms still work in the configure build and in any makefile
5392 build that builds pnglibconf.h, although the feature selection macros
5393 have changed somewhat as described above. In 1.5.0, however, pngusr.h is
5394 processed only once, when the exported header file pnglibconf.h is built.
5395 pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
5396 build of pnglibconf.h and it is never included in an application build.
5398 The rarely used alternative of adding a list of feature macros to the
5399 CFLAGS setting in the build also still works; however, the macros will be
5400 copied to pnglibconf.h and this may produce macro redefinition warnings
5401 when the individual C files are compiled.
5403 All configuration now only works if pnglibconf.h is built from
5404 scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
5405 (the original author of awk) maintains C source code of that awk and this
5406 and all known later implementations (often called by subtly different
5407 names - nawk and gawk for example) are adequate to build pnglibconf.h.
5408 The Sun Microsystems (now Oracle) program 'awk' is an earlier version
5409 and does not work; this may also apply to other systems that have a
5410 functioning awk called 'nawk'.
5412 Configuration options are now documented in scripts/pnglibconf.dfa. This
5413 file also includes dependency information that ensures a configuration is
5414 consistent; that is, if a feature is switched off dependent features are
5415 also removed. As a recommended alternative to using feature macros in
5416 pngusr.h a system builder may also define equivalent options in pngusr.dfa
5417 (or, indeed, any file) and add that to the configuration by setting
5418 DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
5419 how to do this, and a case where pngusr.h is still required.
5421 .SH XII. Changes to Libpng from version 1.5.x to 1.6.x
5423 A "simplified API" has been added (see documentation in png.h and a simple
5424 example in contrib/examples/pngtopng.c). The new publicly visible API
5425 includes the following:
5434 png_image_begin_read_from_file()
5435 png_image_begin_read_from_stdio()
5436 png_image_begin_read_from_memory()
5437 png_image_finish_read()
5440 png_image_write_to_file()
5441 png_image_write_to_stdio()
5443 Starting with libpng-1.6.0, you can configure libpng to prefix all exported
5444 symbols, using the PNG_PREFIX macro.
5446 We no longer include string.h in png.h. The include statement has been moved
5447 to pngpriv.h, where it is not accessible by applications. Applications that
5448 need access to information in string.h must add an '#include "string.h"'
5449 directive. It does not matter whether this is placed prior to or after
5450 the '"#include png.h"' directive.
5452 The following API are now DEPRECATED:
5454 png_convert_to_rfc1123() which has been replaced
5455 with png_convert_to_rfc1123_buffer()
5457 png_malloc_default()
5461 The following has been removed:
5462 png_get_io_chunk_name(), which has been replaced
5463 with png_get_io_chunk_type(). The new
5464 function returns a 32-bit integer instead of
5466 The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
5467 png_memset() macros are no longer used in the libpng sources and
5468 have been removed. These had already been made invisible to applications
5469 (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
5471 The signatures of many exported functions were changed, such that
5472 png_structp became png_structrp or png_const_structrp
5473 png_infop became png_inforp or png_const_inforp
5474 where "rp" indicates a "restricted pointer".
5476 Error detection in some chunks has improved; in particular the iCCP chunk
5477 reader now does pretty complete validation of the basic format. Some bad
5478 profiles that were previously accepted are now rejected, in particular the
5479 very old broken Microsoft/HP sRGB profile.
5481 The library now issues a warning if both background processing and RGB to
5482 gray are used when gamma correction happens. As with previous versions of
5483 the library the results are numerically very incorrect in this case.
5485 There are some minor arithmetic changes in some transforms such as
5486 png_set_background(), that might be detected by certain regression tests.
5488 Unknown chunk handling has been improved internally, without any API change.
5489 This adds more correct option control of the unknown handling, corrects
5490 a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
5491 it possible to skip IDAT chunks in the sequential reader.
5493 The machine-generated configure files are no longer included in branches
5494 libpng16 and later of the GIT repository. They continue to be included
5495 in the tarball releases, however.
5497 .SH XIII. Detecting libpng
5499 The png_get_io_ptr() function has been present since libpng-0.88, has never
5500 changed, and is unaffected by conditional compilation macros. It is the
5501 best choice for use in configure scripts for detecting the presence of any
5502 libpng version since 0.88. In an autoconf "configure.in" you could use
5504 AC_CHECK_LIB(png, png_get_io_ptr, ...
5506 .SH XV. Source code repository
5508 Since about February 2009, version 1.2.34, libpng has been under "git" source
5509 control. The git repository was built from old libpng-x.y.z.tar.gz files
5510 going back to version 0.70. You can access the git repository (read only)
5513 git://libpng.git.sourceforge.net/gitroot/libpng
5515 or you can browse it via "gitweb" at
5517 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
5519 Patches can be sent to glennrp at users.sourceforge.net or to
5520 png-mng-implement at lists.sourceforge.net or you can upload them to
5521 the libpng bug tracker at
5523 http://libpng.sourceforge.net
5525 We also accept patches built from the tar or zip distributions, and
5526 simple verbal discriptions of bug fixes, reported either to the
5527 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5528 mailing list, or directly to glennrp.
5530 .SH XV. Coding style
5532 Our coding style is similar to the "Allman" style, with curly
5533 braces on separate lines:
5540 else if (another condition)
5545 The braces can be omitted from simple one-line actions:
5550 We use 3-space indentation, except for continued statements which
5551 are usually indented the same as the first line of the statement
5552 plus four more spaces.
5554 For macro definitions we use 2-space indentation, always leaving the "#"
5555 in the first column.
5557 #ifndef PNG_NO_FEATURE
5558 # ifndef PNG_FEATURE_SUPPORTED
5559 # define PNG_FEATURE_SUPPORTED
5563 Comments appear with the leading "/*" at the same indentation as
5564 the statement that follows the comment:
5566 /* Single-line comment */
5569 /* This is a multiple-line
5574 Very short comments can be placed after the end of the statement
5575 to which they pertain:
5577 statement; /* comment */
5579 We don't use C++ style ("//") comments. We have, however,
5580 used them in the past in some now-abandoned MMX assembler
5583 Functions and their curly braces are not indented, and
5584 exported functions are marked with PNGAPI:
5586 /* This is a public function that is visible to
5587 * application programmers. It does thus-and-so.
5590 png_exported_function(png_ptr, png_info, foo)
5595 The prototypes for all exported functions appear in png.h,
5596 above the comment that says
5598 /* Maintainer: Put new public prototypes here ... */
5600 We mark all non-exported functions with "/* PRIVATE */"":
5603 png_non_exported_function(png_ptr, png_info, foo)
5608 The prototypes for non-exported functions (except for those in
5611 above the comment that says
5613 /* Maintainer: Put new private prototypes here ^ */
5615 We put a space after the "sizeof" operator and we omit the
5616 optional parentheses around its argument when the argument
5617 is an expression, not a type name, and we always enclose the
5618 sizeof operator, with its argument, in parentheses:
5620 (sizeof (png_uint_32))
5623 Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
5624 though it were a function.
5626 To avoid polluting the global namespace, the names of all exported
5627 functions and variables begin with "png_", and all publicly visible C
5628 preprocessor macros begin with "PNG". We request that applications that
5629 use libpng *not* begin any of their own symbols with either of these strings.
5631 We put a space after each comma and after each semicolon
5632 in "for" statements, and we put spaces before and after each
5633 C binary operator and after "for" or "while", and before
5634 "?". We don't put a space between a typecast and the expression
5635 being cast, nor do we put one between a function name and the
5636 left parenthesis that follows it:
5638 for (i = 2; i > 0; --i)
5639 y[i] = a(x) + (int)b;
5641 We prefer #ifdef and #ifndef to #if defined() and #if !defined()
5642 when there is only one macro being tested.
5644 We prefer to express integers that are used as bit masks in hex format,
5645 with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5647 We prefer to use underscores in variable names rather than camelCase, except
5648 for a few type names that we inherit from zlib.h.
5650 We do not use the TAB character for indentation in the C sources.
5652 Lines do not exceed 80 characters.
5654 Other rules can be inferred by inspecting the libpng source.
5656 .SH XVI. Y2K Compliance in libpng
5660 Since the PNG Development group is an ad-hoc body, we can't make
5661 an official declaration.
5663 This is your unofficial assurance that libpng from version 0.71 and
5664 upward through 1.6.0 are Y2K compliant. It is my belief that earlier
5665 versions were also Y2K compliant.
5667 Libpng only has two year fields. One is a 2-byte unsigned integer
5668 that will hold years up to 65535. The other, which is deprecated,
5669 holds the date in text format, and will hold years up to 9999.
5672 "png_uint_16 year" in png_time_struct.
5675 "char time_buffer[29]" in png_struct. This is no longer used
5676 in libpng-1.6.x and will be removed from libpng-1.7.0.
5678 There are seven time-related functions:
5680 png_convert_to_rfc_1123() in png.c
5681 (formerly png_convert_to_rfc_1152() in error)
5682 png_convert_from_struct_tm() in pngwrite.c, called
5684 png_convert_from_time_t() in pngwrite.c
5685 png_get_tIME() in pngget.c
5686 png_handle_tIME() in pngrutil.c, called in pngread.c
5687 png_set_tIME() in pngset.c
5688 png_write_tIME() in pngwutil.c, called in pngwrite.c
5690 All appear to handle dates properly in a Y2K environment. The
5691 png_convert_from_time_t() function calls gmtime() to convert from system
5692 clock time, which returns (year - 1900), which we properly convert to
5693 the full 4-digit year. There is a possibility that applications using
5694 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5695 function, or that they are incorrectly passing only a 2-digit year
5696 instead of "year - 1900" into the png_convert_from_struct_tm() function,
5697 but this is not under our control. The libpng documentation has always
5698 stated that it works with 4-digit years, and the APIs have been
5701 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5702 integer to hold the year, and can hold years as large as 65535.
5704 zlib, upon which libpng depends, is also Y2K compliant. It contains
5705 no date-related code.
5708 Glenn Randers-Pehrson
5710 PNG Development Group
5714 Note about libpng version numbers:
5716 Due to various miscommunications, unforeseen code incompatibilities
5717 and occasional factors outside the authors' control, version numbering
5718 on the library has not always been consistent and straightforward.
5719 The following table summarizes matters since version 0.89c, which was
5720 the first widely used release:
5722 source png.h png.h shared-lib
5723 version string int version
5724 ------- ------ ----- ----------
5725 0.89c ("beta 3") 0.89 89 1.0.89
5726 0.90 ("beta 4") 0.90 90 0.90
5727 0.95 ("beta 5") 0.95 95 0.95
5728 0.96 ("beta 6") 0.96 96 0.96
5729 0.97b ("beta 7") 1.00.97 97 1.0.1
5730 0.97c 0.97 97 2.0.97
5733 0.99a-m 0.99 99 2.0.99
5735 1.0.0 1.0.0 100 2.1.0
5736 1.0.0 (from here on, the 100 2.1.0
5737 1.0.1 png.h string is 10001 2.1.0
5738 1.0.1a-e identical to the 10002 from here on, the
5739 1.0.2 source version) 10002 shared library is 2.V
5740 1.0.2a-b 10003 where V is the source
5741 1.0.1 10001 code version except as
5742 1.0.1a-e 10002 2.1.0.1a-e noted.
5744 1.0.2a-b 10003 2.1.0.2a-b
5746 1.0.3a-d 10004 2.1.0.3a-d
5748 1.0.4a-f 10005 2.1.0.4a-f
5749 1.0.5 (+ 2 patches) 10005 2.1.0.5
5750 1.0.5a-d 10006 2.1.0.5a-d
5751 1.0.5e-r 10100 2.1.0.5e-r
5752 1.0.5s-v 10006 2.1.0.5s-v
5753 1.0.6 (+ 3 patches) 10006 2.1.0.6
5754 1.0.6d-g 10007 2.1.0.6d-g
5757 1.0.6j 10007 2.1.0.6j
5758 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5759 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5760 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5761 1.0.7 1 10007 2.1.0.7
5762 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5763 1.0.8rc1 1 10008 2.1.0.8rc1
5764 1.0.8 1 10008 2.1.0.8
5765 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5766 1.0.9rc1 1 10009 2.1.0.9rc1
5767 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5768 1.0.9rc2 1 10009 2.1.0.9rc2
5769 1.0.9 1 10009 2.1.0.9
5770 1.0.10beta1 1 10010 2.1.0.10beta1
5771 1.0.10rc1 1 10010 2.1.0.10rc1
5772 1.0.10 1 10010 2.1.0.10
5773 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5774 1.0.11rc1 1 10011 2.1.0.11rc1
5775 1.0.11 1 10011 2.1.0.11
5776 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5777 1.0.12rc1 2 10012 2.1.0.12rc1
5778 1.0.12 2 10012 2.1.0.12
5779 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5780 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5781 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5782 1.2.0rc1 3 10200 3.1.2.0rc1
5783 1.2.0 3 10200 3.1.2.0
5784 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5785 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5786 1.2.1 3 10201 3.1.2.1
5787 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5788 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5789 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5790 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5791 1.0.13 10 10013 10.so.0.1.0.13
5792 1.2.2 12 10202 12.so.0.1.2.2
5793 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5794 1.2.3 12 10203 12.so.0.1.2.3
5795 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5796 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5797 1.0.14 10 10014 10.so.0.1.0.14
5798 1.2.4 13 10204 12.so.0.1.2.4
5799 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5800 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5801 1.0.15 10 10015 10.so.0.1.0.15
5802 1.2.5 13 10205 12.so.0.1.2.5
5803 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5804 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5805 1.0.16 10 10016 10.so.0.1.0.16
5806 1.2.6 13 10206 12.so.0.1.2.6
5807 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5808 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5809 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5810 1.0.17 10 10017 12.so.0.1.0.17
5811 1.2.7 13 10207 12.so.0.1.2.7
5812 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5813 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5814 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5815 1.0.18 10 10018 12.so.0.1.0.18
5816 1.2.8 13 10208 12.so.0.1.2.8
5817 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5818 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5819 1.2.9rc1 13 10209 12.so.0.9[.0]
5820 1.2.9 13 10209 12.so.0.9[.0]
5821 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5822 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5823 1.2.10 13 10210 12.so.0.10[.0]
5824 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5825 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5826 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5827 1.2.11 13 10211 12.so.0.11[.0]
5828 1.2.12 13 10212 12.so.0.12[.0]
5829 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5830 1.2.13 13 10213 12.so.0.13[.0]
5831 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5832 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5833 1.4.0rc01 14 10400 14.so.14.0[.0]
5834 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5835 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5836 1.4.0 14 10400 14.so.14.0[.0]
5837 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5838 1.4.1rc01 14 10401 14.so.14.1[.0]
5839 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5840 1.4.1 14 10401 14.so.14.1[.0]
5841 1.4.2 14 10402 14.so.14.2[.0]
5842 1.4.3 14 10403 14.so.14.3[.0]
5843 1.4.4 14 10404 14.so.14.4[.0]
5844 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5845 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5846 1.5.0 15 10500 15.so.15.0[.0]
5847 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5848 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5849 1.5.1 15 10501 15.so.15.1[.0]
5850 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5851 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5852 1.5.2 15 10502 15.so.15.2[.0]
5853 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5854 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5855 1.5.3beta11 15 10503 15.so.15.3[.0]
5857 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5858 1.5.4rc01 15 10504 15.so.15.4[.0]
5859 1.5.4 15 10504 15.so.15.4[.0]
5860 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5861 1.5.5rc01 15 10505 15.so.15.5[.0]
5862 1.5.5 15 10505 15.so.15.5[.0]
5863 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5864 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5865 1.5.6 15 10506 15.so.15.6[.0]
5866 1.5.7beta01-05 15 10507 15.so.15.7[.0]
5867 1.5.7rc01-03 15 10507 15.so.15.7[.0]
5868 1.5.7 15 10507 15.so.15.7[.0]
5869 1.6.0beta01-40 16 10600 16.so.16.0[.0]
5870 1.6.0rc01-08 16 10600 16.so.16.0[.0]
5871 1.6.0 16 10600 16.so.16.0[.0]
5873 Henceforth the source version will match the shared-library minor
5874 and patch numbers; the shared-library major version number will be
5875 used for changes in backward compatibility, as it is intended. The
5876 PNG_PNGLIB_VER macro, which is not used within libpng but is available
5877 for applications, is an unsigned integer of the form xyyzz corresponding
5878 to the source version x.y.z (leading zeros in y and z). Beta versions
5879 were given the previous public release number plus a letter, until
5880 version 1.0.6j; from then on they were given the upcoming public
5881 release number plus "betaNN" or "rcN".
5884 .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5889 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5890 http://www.libpng.org/pub/png
5895 (generally) at the same location as
5899 ftp://ftp.info-zip.org/pub/infozip/zlib
5902 .IR PNG specification: RFC 2083
5904 (generally) at the same location as
5908 ftp://ds.internic.net/rfc/rfc2083.txt
5910 or (as a W3C Recommendation) at
5912 http://www.w3.org/TR/REC-png.html
5915 In the case of any inconsistency between the PNG specification
5916 and this library, the specification takes precedence.
5919 This man page: Glenn Randers-Pehrson
5920 <glennrp at users.sourceforge.net>
5922 The contributing authors would like to thank all those who helped
5923 with testing, bug fixes, and patience. This wouldn't have been
5924 possible without all of you.
5926 Thanks to Frank J. T. Wojcik for helping with the documentation.
5928 Libpng version 1.6.0 - February 14, 2013:
5929 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5930 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5932 Supported by the PNG development group
5934 png-mng-implement at lists.sf.net
5935 (subscription required; visit
5936 png-mng-implement at lists.sourceforge.net (subscription required; visit
5937 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5940 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5942 (This copy of the libpng notices is provided for your convenience. In case of
5943 any discrepancy between this copy and the notices in the file png.h that is
5944 included in the libpng distribution, the latter shall prevail.)
5946 If you modify libpng you may insert additional notices immediately following
5949 This code is released under the libpng license.
5951 libpng versions 1.2.6, August 15, 2004, through 1.6.0, February 14, 2013, are
5952 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5953 distributed according to the same disclaimer and license as libpng-1.2.5
5954 with the following individual added to the list of Contributing Authors
5958 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5959 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5960 distributed according to the same disclaimer and license as libpng-1.0.6
5961 with the following individuals added to the list of Contributing Authors
5963 Simon-Pierre Cadieux
5967 and with the following additions to the disclaimer:
5969 There is no warranty against interference with your
5970 enjoyment of the library or against infringement.
5971 There is no warranty that our efforts or the library
5972 will fulfill any of your particular purposes or needs.
5973 This library is provided with all faults, and the entire
5974 risk of satisfactory quality, performance, accuracy, and
5975 effort is with the user.
5977 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5978 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5979 Distributed according to the same disclaimer and license as libpng-0.96,
5980 with the following individuals added to the list of Contributing Authors:
5983 Glenn Randers-Pehrson
5986 libpng versions 0.89, June 1996, through 0.96, May 1997, are
5987 Copyright (c) 1996, 1997 Andreas Dilger
5988 Distributed according to the same disclaimer and license as libpng-0.88,
5989 with the following individuals added to the list of Contributing Authors:
5998 libpng versions 0.5, May 1995, through 0.88, January 1996, are
5999 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
6001 For the purposes of this copyright and license, "Contributing Authors"
6002 is defined as the following set of individuals:
6010 The PNG Reference Library is supplied "AS IS". The Contributing Authors
6011 and Group 42, Inc. disclaim all warranties, expressed or implied,
6012 including, without limitation, the warranties of merchantability and of
6013 fitness for any purpose. The Contributing Authors and Group 42, Inc.
6014 assume no liability for direct, indirect, incidental, special, exemplary,
6015 or consequential damages, which may result from the use of the PNG
6016 Reference Library, even if advised of the possibility of such damage.
6018 Permission is hereby granted to use, copy, modify, and distribute this
6019 source code, or portions hereof, for any purpose, without fee, subject
6020 to the following restrictions:
6022 1. The origin of this source code must not be misrepresented.
6024 2. Altered versions must be plainly marked as such and
6025 must not be misrepresented as being the original source.
6027 3. This Copyright notice may not be removed or altered from
6028 any source or altered source distribution.
6030 The Contributing Authors and Group 42, Inc. specifically permit, without
6031 fee, and encourage the use of this source code as a component to
6032 supporting the PNG file format in commercial products. If you use this
6033 source code in a product, acknowledgment is not required but would be
6037 A "png_get_copyright" function is available, for convenient use in "about"
6040 printf("%s",png_get_copyright(NULL));
6042 Also, the PNG logo (in PNG format, of course) is supplied in the
6043 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
6045 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
6046 certification mark of the Open Source Initiative.
6048 Glenn Randers-Pehrson
6049 glennrp at users.sourceforge.net