1 .TH LIBPNG 3 "January 24, 2013"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.5.14
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_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
116 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
118 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
120 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
122 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
124 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
126 \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
128 \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
130 \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
132 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
134 \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
136 \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
138 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
140 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
142 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
144 \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
146 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
148 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
150 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
152 \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
154 \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
156 \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
158 \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
160 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
162 \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
164 \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
166 \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
168 \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
170 \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
172 \fB/* This function is really an inline macro. \fI*/
174 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
176 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
178 \fB/* This function is really an inline macro. \fI*/
180 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
182 \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
184 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
186 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
188 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
190 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
192 \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
194 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
196 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
198 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
200 \fBpng_int_32 png_get_x_offset_pixels (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_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
204 \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
206 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
208 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
210 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
212 \fBpng_int_32 png_get_y_offset_pixels (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_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
216 \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
218 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
220 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
222 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
224 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
226 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
228 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
230 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
232 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
234 \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
236 \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
238 \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
240 \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
242 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
244 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
246 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
248 \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
250 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
252 \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
254 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
256 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
258 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
260 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
262 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
264 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
266 \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
268 \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
270 \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
272 \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
274 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
276 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
278 \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
280 \fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
282 \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
284 \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
286 \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
288 \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
290 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
292 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
294 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
296 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
298 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
300 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
302 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
304 \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
306 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
308 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
310 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
312 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
314 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
316 \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
318 \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
320 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
322 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
324 \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
326 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
328 \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
330 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
332 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
334 \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
336 \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
338 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
340 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
342 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
344 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
346 \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
348 \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
350 \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
352 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
354 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
356 \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
358 \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
360 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
362 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
364 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
366 \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
368 \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
370 \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
372 \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
374 \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
376 \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
378 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
380 \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
382 \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
384 \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
386 \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
388 \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
390 \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
392 \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
394 \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
396 \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
398 \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
400 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
402 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
404 \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
406 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
408 \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
410 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
412 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
414 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
416 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
418 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
420 \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
422 \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
424 \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
426 \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
428 \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
430 \fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
432 \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
434 \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
436 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
438 \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
440 \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
442 \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
444 \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
446 \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
448 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
450 \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
452 \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
454 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
456 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
458 \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
460 \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
462 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
464 \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
466 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
468 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
470 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
472 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
474 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
476 \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
478 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
480 \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
482 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
487 library supports encoding, decoding, and various manipulations of
488 the Portable Network Graphics (PNG) format image files. It uses the
491 Following is a copy of the libpng-manual.txt file that accompanies libpng.
493 Libpng-manual.txt - A description on how to use and modify libpng
495 libpng version 1.5.14 - January 24, 2013
496 Updated and distributed by Glenn Randers-Pehrson
497 <glennrp at users.sourceforge.net>
498 Copyright (c) 1998-2012 Glenn Randers-Pehrson
500 This document is released under the libpng license.
501 For conditions of distribution and use, see the disclaimer
506 libpng versions 0.97, January 1998, through 1.5.14 - January 24, 2013
507 Updated and distributed by Glenn Randers-Pehrson
508 Copyright (c) 1998-2012 Glenn Randers-Pehrson
510 libpng 1.0 beta 6 version 0.96 May 28, 1997
511 Updated and distributed by Andreas Dilger
512 Copyright (c) 1996, 1997 Andreas Dilger
514 libpng 1.0 beta 2 - version 0.88 January 26, 1996
515 For conditions of distribution and use, see copyright
516 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
517 Schalnat, Group 42, Inc.
519 Updated/rewritten per request in the libpng FAQ
520 Copyright (c) 1995, 1996 Frank J. T. Wojcik
521 December 18, 1995 & January 20, 1996
525 This file describes how to use and modify the PNG reference library
526 (known as libpng) for your own use. There are five sections to this
527 file: introduction, structures, reading, writing, and modification and
528 configuration notes for various special platforms. In addition to this
529 file, example.c is a good starting point for using the library, as
530 it is heavily commented and should include everything most people
531 will need. We assume that libpng is already installed; see the
532 INSTALL file for instructions on how to install libpng.
534 For examples of libpng usage, see the files "example.c", "pngtest.c",
535 and the files in the "contrib" directory, all of which are included in
536 the libpng distribution.
538 Libpng was written as a companion to the PNG specification, as a way
539 of reducing the amount of time and effort it takes to support the PNG
540 file format in application programs.
542 The PNG specification (second edition), November 2003, is available as
543 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
544 <http://www.w3.org/TR/2003/REC-PNG-20031110/
545 The W3C and ISO documents have identical technical content.
547 The PNG-1.2 specification is available at
548 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
549 to the PNG specification (second edition) but has some additional material.
551 The PNG-1.0 specification is available
552 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
553 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
555 Some additional chunks are described in the special-purpose public chunks
556 documents at <http://www.libpng.org/pub/png/documents/>.
559 about PNG, and the latest version of libpng, can be found at the PNG home
560 page, <http://www.libpng.org/pub/png/>.
562 Most users will not have to modify the library significantly; advanced
563 users may want to modify it more. All attempts were made to make it as
564 complete as possible, while keeping the code easy to understand.
565 Currently, this library only supports C. Support for other languages
568 Libpng has been designed to handle multiple sessions at one time,
569 to be easily modifiable, to be portable to the vast majority of
570 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
571 to use. The ultimate goal of libpng is to promote the acceptance of
572 the PNG file format in whatever way possible. While there is still
573 work to be done (see the TODO file), libpng should cover the
574 majority of the needs of its users.
576 Libpng uses zlib for its compression and decompression of PNG files.
577 Further information about zlib, and the latest version of zlib, can
578 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
579 The zlib compression utility is a general purpose utility that is
580 useful for more than PNG files, and can be used without libpng.
581 See the documentation delivered with zlib for more details.
582 You can usually find the source files for the zlib utility wherever you
583 find the libpng source files.
585 Libpng is thread safe, provided the threads are using different
586 instances of the structures. Each thread should have its own
587 png_struct and png_info instances, and thus its own image.
588 Libpng does not protect itself against two threads using the
589 same instance of a structure.
593 There are two main structures that are important to libpng, png_struct
594 and png_info. Both are internal structures that are no longer exposed
595 in the libpng interface (as of libpng 1.5.0).
597 The png_info structure is designed to provide information about the
598 PNG file. At one time, the fields of png_info were intended to be
599 directly accessible to the user. However, this tended to cause problems
600 with applications using dynamically loaded libraries, and as a result
601 a set of interface functions for png_info (the png_get_*() and png_set_*()
602 functions) was developed, and direct access to the png_info fields was
605 The png_struct structure is the object used by the library to decode a
606 single image. As of 1.5.0 this structure is also not exposed.
608 Almost all libpng APIs require a pointer to a png_struct as the first argument.
609 Many (in particular the png_set and png_get APIs) also require a pointer
610 to png_info as the second argument. Some application visible macros
611 defined in png.h designed for basic data access (reading and writing
612 integers in the PNG format) don't take a png_info pointer, but it's almost
613 always safe to assume that a (png_struct*) has to be passed to call an API
616 You can have more than one png_info structure associated with an image,
617 as illustrated in pngtest.c, one for information valid prior to the
618 IDAT chunks and another (called "end_info" below) for things after them.
620 The png.h header file is an invaluable reference for programming with libpng.
621 And while I'm on the topic, make sure you include the libpng header file:
625 and also (as of libpng-1.5.0) the zlib header file, if you need it:
631 The png.h header file defines a number of integral types used by the
632 APIs. Most of these are fairly obvious; for example types corresponding
633 to integers of particular sizes and types for passing color values.
635 One exception is how non-integral numbers are handled. For application
636 convenience most APIs that take such numbers have C (double) arguments;
637 however, internally PNG, and libpng, use 32 bit signed integers and encode
638 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
639 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
640 which is simply (png_int_32).
642 All APIs that take (double) arguments also have a matching API that
643 takes the corresponding fixed point integer arguments. The fixed point
644 API has the same name as the floating point one with "_fixed" appended.
645 The actual range of values permitted in the APIs is frequently less than
646 the full range of (png_fixed_point) (-21474 to +21474). When APIs require
647 a non-negative argument the type is recorded as png_uint_32 above. Consult
648 the header file and the text below for more information.
650 Special care must be take with sCAL chunk handling because the chunk itself
651 uses non-integral values encoded as strings containing decimal floating point
652 numbers. See the comments in the header file.
656 The main header file function declarations are frequently protected by C
657 preprocessing directives of the form:
659 #ifdef PNG_feature_SUPPORTED
663 #ifdef PNG_feature_SUPPORTED
667 The library can be built without support for these APIs, although a
668 standard build will have all implemented APIs. Application programs
669 should check the feature macros before using an API for maximum
670 portability. From libpng 1.5.0 the feature macros set during the build
671 of libpng are recorded in the header file "pnglibconf.h" and this file
672 is always included by png.h.
674 If you don't need to change the library configuration from the default, skip to
675 the next section ("Reading").
677 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
678 of the build project files in the 'projects' directory simply copy
679 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
680 systems do not permit easy auto-configuration of the library - they only
681 support the default configuration.
683 The easiest way to make minor changes to the libpng configuration when
684 auto-configuration is supported is to add definitions to the command line
685 using (typically) CPPFLAGS. For example:
687 CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
689 will change the internal libpng math implementation for gamma correction and
690 other arithmetic calculations to fixed point, avoiding the need for fast
691 floating point support. The result can be seen in the generated pnglibconf.h -
692 make sure it contains the changed feature macro setting.
694 If you need to make more extensive configuration changes - more than one or two
695 feature macro settings - you can either add -DPNG_USER_CONFIG to the build
696 command line and put a list of feature macro settings in pngusr.h or you can set
697 DFA_XTRA (a makefile variable) to a file containing the same information in the
698 form of 'option' settings.
700 A. Changing pnglibconf.h
702 A variety of methods exist to build libpng. Not all of these support
703 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
704 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
706 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
707 pnglibconf.h and changing the lines defining the supported features, paying
708 very close attention to the 'option' information in scripts/pnglibconf.dfa
709 that describes those features and their requirements. This is easy to get
712 B. Configuration using DFA_XTRA
714 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
715 variant such as 'nawk' or 'gawk', is available. The configure build will
716 automatically find an appropriate awk and build pnglibconf.h.
717 The scripts/pnglibconf.mak file contains a set of make rules for doing the
718 same thing if configure is not used, and many of the makefiles in the scripts
719 directory use this approach.
721 When rebuilding simply write a new file containing changed options and set
722 DFA_XTRA to the name of this file. This causes the build to append the new file
723 to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
724 of the following forms:
728 This turns all optional features off. Include it at the start of pngusr.dfa to
729 make it easier to build a minimal configuration. You will need to turn at least
730 some features on afterward to enable either reading or writing code, or both.
735 Enable or disable a single feature. This will automatically enable other
736 features required by a feature that is turned on or disable other features that
737 require a feature which is turned off. Conflicting settings will cause an error
738 message to be emitted by awk.
740 setting feature default value
742 Changes the default value of setting 'feature' to 'value'. There are a small
743 number of settings listed at the top of pnglibconf.h, they are documented in the
744 source code. Most of these values have performance implications for the library
745 but most of them have no visible effect on the API. Some can also be overridden
748 This method of building a customized pnglibconf.h is illustrated in
749 contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
750 pngusr.dfa in these directories.
752 C. Configuration using PNG_USR_CONFIG
754 If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
755 pngusr.h will automatically be included before the options in
756 scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
757 macro definitions turning features on or off or setting settings.
759 Apart from the global setting "everything = off" all the options listed above
760 can be set using macros in pngusr.h:
762 #define PNG_feature_SUPPORTED
768 #define PNG_NO_feature
774 #define PNG_feature value
778 setting feature default value
780 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
781 pngusr file you supply override the contents of scripts/pnglibconf.dfa
783 If confusing or incomprehensible behavior results it is possible to
784 examine the intermediate file pnglibconf.dfn to find the full set of
785 dependency information for each setting and option. Simply locate the
786 feature in the file and read the C comments that precede it.
788 This method is also illustrated in the contrib/pngminim/* makefiles and
793 We'll now walk you through the possible functions to call when reading
794 in a PNG file sequentially, briefly explaining the syntax and purpose
795 of each one. See example.c and png.h for more detail. While
796 progressive reading is covered in the next section, you will still
797 need some of the functions discussed in this section to read a PNG
802 You will want to do the I/O initialization(*) before you get into libpng,
803 so if it doesn't work, you don't have much to undo. Of course, you
804 will also want to insure that you are, in fact, dealing with a PNG
805 file. Libpng provides a simple check to see if a file is a PNG file.
806 To use it, pass in the first 1 to 8 bytes of the file to the function
807 png_sig_cmp(), and it will return 0 (false) if the bytes match the
808 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
809 Of course, the more bytes you pass in, the greater the accuracy of the
812 If you are intending to keep the file pointer open for use in libpng,
813 you must ensure you don't read more than 8 bytes from the beginning
814 of the file, and you also have to make a call to png_set_sig_bytes_read()
815 with the number of bytes you read from the beginning. Libpng will
816 then only check the bytes (if any) that your program didn't read.
818 (*): If you are not using the standard I/O functions, you will need
819 to replace them with custom functions. See the discussion under
823 FILE *fp = fopen(file_name, "rb");
829 fread(header, 1, number, fp);
830 is_png = !png_sig_cmp(header, 0, number);
838 Next, png_struct and png_info need to be allocated and initialized. In
839 order to ensure that the size of these structures is correct even with a
840 dynamically linked libpng, there are functions to initialize and
841 allocate the structures. We also pass the library version, optional
842 pointers to error handling functions, and a pointer to a data struct for
843 use by the error functions, if necessary (the pointer and functions can
844 be NULL if the default error handlers are to be used). See the section
845 on Changes to Libpng below regarding the old initialization functions.
846 The structure allocation functions quietly return NULL if they fail to
847 create the structure, so your application should check for that.
849 png_structp png_ptr = png_create_read_struct
850 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
851 user_error_fn, user_warning_fn);
856 png_infop info_ptr = png_create_info_struct(png_ptr);
860 png_destroy_read_struct(&png_ptr,
861 (png_infopp)NULL, (png_infopp)NULL);
865 If you want to use your own memory allocation routines,
866 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
867 png_create_read_struct_2() instead of png_create_read_struct():
869 png_structp png_ptr = png_create_read_struct_2
870 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
871 user_error_fn, user_warning_fn, (png_voidp)
872 user_mem_ptr, user_malloc_fn, user_free_fn);
874 The error handling routines passed to png_create_read_struct()
875 and the memory alloc/free routines passed to png_create_struct_2()
876 are only necessary if you are not using the libpng supplied error
877 handling and memory alloc/free functions.
879 When libpng encounters an error, it expects to longjmp back
880 to your routine. Therefore, you will need to call setjmp and pass
881 your png_jmpbuf(png_ptr). If you read the file from different
882 routines, you will need to update the longjmp buffer every time you enter
883 a new routine that will call a png_*() function.
885 See your documentation of setjmp/longjmp for your compiler for more
886 information on setjmp/longjmp. See the discussion on libpng error
887 handling in the Customizing Libpng section below for more information
888 on the libpng error handling. If an error occurs, and libpng longjmp's
889 back to your setjmp, you will want to call png_destroy_read_struct() to
892 if (setjmp(png_jmpbuf(png_ptr)))
894 png_destroy_read_struct(&png_ptr, &info_ptr,
900 Pass (png_infopp)NULL instead of &end_info if you didn't create
901 an end_info structure.
903 If you would rather avoid the complexity of setjmp/longjmp issues,
904 you can compile libpng with PNG_NO_SETJMP, in which case
905 errors will result in a call to PNG_ABORT() which defaults to abort().
907 You can #define PNG_ABORT() to a function that does something
908 more useful than abort(), as long as your function does not
911 Now you need to set up the input code. The default for libpng is to
912 use the C function fread(). If you use this, you will need to pass a
913 valid FILE * in the function png_init_io(). Be sure that the file is
914 opened in binary mode. If you wish to handle reading data in another
915 way, you need not call the png_init_io() function, but you must then
916 implement the libpng I/O methods discussed in the Customizing Libpng
919 png_init_io(png_ptr, fp);
921 If you had previously opened the file and read any of the signature from
922 the beginning in order to see if this was a PNG file, you need to let
923 libpng know that there are some bytes missing from the start of the file.
925 png_set_sig_bytes(png_ptr, number);
927 You can change the zlib compression buffer size to be used while
928 reading compressed data with
930 png_set_compression_buffer_size(png_ptr, buffer_size);
932 where the default size is 8192 bytes. Note that the buffer size
933 is changed immediately and the buffer is reallocated immediately,
934 instead of setting a flag to be acted upon later.
936 If you want CRC errors to be handled in a different manner than
939 png_set_crc_action(png_ptr, crit_action, ancil_action);
941 The values for png_set_crc_action() say how libpng is to handle CRC errors in
942 ancillary and critical chunks, and whether to use the data contained
943 therein. Note that it is impossible to "discard" data in a critical
946 Choices for (int) crit_action are
947 PNG_CRC_DEFAULT 0 error/quit
948 PNG_CRC_ERROR_QUIT 1 error/quit
949 PNG_CRC_WARN_USE 3 warn/use data
950 PNG_CRC_QUIET_USE 4 quiet/use data
951 PNG_CRC_NO_CHANGE 5 use the current value
953 Choices for (int) ancil_action are
954 PNG_CRC_DEFAULT 0 error/quit
955 PNG_CRC_ERROR_QUIT 1 error/quit
956 PNG_CRC_WARN_DISCARD 2 warn/discard data
957 PNG_CRC_WARN_USE 3 warn/use data
958 PNG_CRC_QUIET_USE 4 quiet/use data
959 PNG_CRC_NO_CHANGE 5 use the current value
961 .SS Setting up callback code
963 You can set up a callback function to handle any unknown chunks in the
964 input stream. You must supply the function
966 read_chunk_callback(png_structp png_ptr,
967 png_unknown_chunkp chunk);
969 /* The unknown chunk structure contains your
970 chunk data, along with similar data for any other
977 /* Note that libpng has already taken care of
980 /* put your code here. Search for your chunk in the
981 unknown chunk structure, process it, and return one
984 return (-n); /* chunk had an error */
985 return (0); /* did not recognize */
986 return (n); /* success */
989 (You can give your function another name that you like instead of
990 "read_chunk_callback")
992 To inform libpng about your function, use
994 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
995 read_chunk_callback);
997 This names not only the callback function, but also a user pointer that
998 you can retrieve with
1000 png_get_user_chunk_ptr(png_ptr);
1002 If you call the png_set_read_user_chunk_fn() function, then all unknown
1003 chunks will be saved when read, in case your callback function will need
1004 one or more of them. This behavior can be changed with the
1005 png_set_keep_unknown_chunks() function, described below.
1007 At this point, you can set up a callback function that will be
1008 called after each row has been read, which you can use to control
1009 a progress meter or the like. It's demonstrated in pngtest.c.
1010 You must supply a function
1012 void read_row_callback(png_structp png_ptr,
1013 png_uint_32 row, int pass);
1015 /* put your code here */
1018 (You can give it another name that you like instead of "read_row_callback")
1020 To inform libpng about your function, use
1022 png_set_read_status_fn(png_ptr, read_row_callback);
1024 When this function is called the row has already been completely processed and
1025 the 'row' and 'pass' refer to the next row to be handled. For the
1026 non-interlaced case the row that was just handled is simply one less than the
1027 passed in row number, and pass will always be 0. For the interlaced case the
1028 same applies unless the row value is 0, in which case the row just handled was
1029 the last one from one of the preceding passes. Because interlacing may skip a
1030 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1031 need to know what the last pass is record (row,pass) from the callback and use
1032 the last recorded value each time.
1034 As with the user transform you can find the output row using the
1035 PNG_ROW_FROM_PASS_ROW macro.
1037 .SS Unknown-chunk handling
1039 Now you get to set the way the library processes unknown chunks in the
1040 input PNG stream. Both known and unknown chunks will be read. Normal
1041 behavior is that known chunks will be parsed into information in
1042 various info_ptr members while unknown chunks will be discarded. This
1043 behavior can be wasteful if your application will never use some known
1044 chunk types. To change this, you can call:
1046 png_set_keep_unknown_chunks(png_ptr, keep,
1047 chunk_list, num_chunks);
1048 keep - 0: default unknown chunk handling
1049 1: ignore; do not keep
1050 2: keep only if safe-to-copy
1051 3: keep even if unsafe-to-copy
1053 You can use these definitions:
1054 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1055 PNG_HANDLE_CHUNK_NEVER 1
1056 PNG_HANDLE_CHUNK_IF_SAFE 2
1057 PNG_HANDLE_CHUNK_ALWAYS 3
1059 chunk_list - list of chunks affected (a byte string,
1060 five bytes per chunk, NULL or '\0' if
1063 num_chunks - number of chunks affected; if 0, all
1064 unknown chunks are affected. If nonzero,
1065 only the chunks in the list are affected
1067 Unknown chunks declared in this way will be saved as raw data onto a
1068 list of png_unknown_chunk structures. If a chunk that is normally
1069 known to libpng is named in the list, it will be handled as unknown,
1070 according to the "keep" directive. If a chunk is named in successive
1071 instances of png_set_keep_unknown_chunks(), the final instance will
1072 take precedence. The IHDR and IEND chunks should not be named in
1073 chunk_list; if they are, libpng will process them normally anyway.
1074 If you know that your application will never make use of some particular
1075 chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1077 Here is an example of the usage of png_set_keep_unknown_chunks(),
1078 where the private "vpAg" chunk will later be processed by a user chunk
1081 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1083 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1084 png_byte unused_chunks[]=
1086 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1087 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1088 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1089 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1090 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1091 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1097 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1098 /* ignore all unknown chunks: */
1099 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1101 /* except for vpAg: */
1102 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1104 /* also ignore unused known chunks: */
1105 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1106 (int)sizeof(unused_chunks)/5);
1111 The PNG specification allows the width and height of an image to be as
1112 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1113 Since very few applications really need to process such large images,
1114 we have imposed an arbitrary 1-million limit on rows and columns.
1115 Larger images will be rejected immediately with a png_error() call. If
1116 you wish to change this limit, you can use
1118 png_set_user_limits(png_ptr, width_max, height_max);
1120 to set your own limits, or use width_max = height_max = 0x7fffffffL
1121 to allow all valid dimensions (libpng may reject some very large images
1122 anyway because of potential buffer overflow conditions).
1124 You should put this statement after you create the PNG structure and
1125 before calling png_read_info(), png_read_png(), or png_process_data().
1127 When writing a PNG datastream, put this statement before calling
1128 png_write_info() or png_write_png().
1130 If you need to retrieve the limits that are being applied, use
1132 width_max = png_get_user_width_max(png_ptr);
1133 height_max = png_get_user_height_max(png_ptr);
1135 The PNG specification sets no limit on the number of ancillary chunks
1136 allowed in a PNG datastream. You can impose a limit on the total number
1137 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1139 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1141 where 0x7fffffffL means unlimited. You can retrieve this limit with
1143 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1145 You can also set a limit on the amount of memory that a compressed chunk
1146 other than IDAT can occupy, with
1148 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1150 and you can retrieve the limit with
1152 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1154 Any chunks that would cause either of these limits to be exceeded will
1157 .SS Information about your system
1159 If you intend to display the PNG or to incorporate it in other image data you
1160 need to tell libpng information about your display or drawing surface so that
1161 libpng can convert the values in the image to match the display.
1163 From libpng-1.5.4 this information can be set before reading the PNG file
1164 header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1165 called before the PNG file header had been read and png_set_alpha_mode() did not
1168 If you need to support versions prior to libpng-1.5.4 test the version number
1169 as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1170 described in the appropriate manual page.
1172 You give libpng the encoding expected by your system expressed as a 'gamma'
1173 value. You can also specify a default encoding for the PNG file in
1174 case the required information is missing from the file. By default libpng
1175 assumes that the PNG data matches your system, to keep this default call:
1177 png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
1179 or you can use the fixed point equivalent:
1181 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma);
1183 If you don't know the gamma for your system it is probably 2.2 - a good
1184 approximation to the IEC standard for display systems (sRGB). If images are
1185 too contrasty or washed out you got the value wrong - check your system
1188 Many systems permit the system gamma to be changed via a lookup table in the
1189 display driver, a few systems, including older Macs, change the response by
1190 default. As of 1.5.4 three special values are available to handle common
1193 PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1
1194 standard. This matches almost all systems.
1195 PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6)
1196 Apple Macintosh system with the default settings.
1197 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the
1198 system expects data with no gamma encoding.
1200 You would use the linear (unencoded) value if you need to process the pixel
1201 values further because this avoids the need to decode and reencode each
1202 component value whenever arithmetic is performed. A lot of graphics software
1203 uses linear values for this reason, often with higher precision component values
1204 to preserve overall accuracy.
1206 The second thing you may need to tell libpng about is how your system handles
1207 alpha channel information. Some, but not all, PNG files contain an alpha
1208 channel. To display these files correctly you need to compose the data onto a
1209 suitable background, as described in the PNG specification.
1211 Libpng only supports composing onto a single color (using png_set_background;
1212 see below). Otherwise you must do the composition yourself and, in this case,
1213 you may need to call png_set_alpha_mode:
1215 #if PNG_LIBPNG_VER >= 10504
1216 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1218 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1221 The screen_gamma value is the same as the argument to png_set_gamma; however,
1222 how it affects the output depends on the mode. png_set_alpha_mode() sets the
1223 file gamma default to 1/screen_gamma, so normally you don't need to call
1224 png_set_gamma. If you need different defaults call png_set_gamma() before
1225 png_set_alpha_mode() - if you call it after it will override the settings made
1226 by png_set_alpha_mode().
1228 The mode is as follows:
1230 PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
1231 green and blue, or gray, components are gamma encoded color
1232 values and are not premultiplied by the alpha value. The
1233 alpha value is a linear measure of the contribution of the
1234 pixel to the corresponding final output pixel.
1236 You should normally use this format if you intend to perform
1237 color correction on the color values; most, maybe all, color
1238 correction software has no handling for the alpha channel and,
1239 anyway, the math to handle pre-multiplied component values is
1240 unnecessarily complex.
1242 Before you do any arithmetic on the component values you need
1243 to remove the gamma encoding and multiply out the alpha
1244 channel. See the PNG specification for more detail. It is
1245 important to note that when an image with an alpha channel is
1246 scaled, linear encoded, pre-multiplied component values must
1249 The remaining modes assume you don't need to do any further color correction or
1250 that if you do, your color correction software knows all about alpha (it
1253 PNG_ALPHA_STANDARD: The data libpng produces
1254 is encoded in the standard way
1255 assumed by most correctly written graphics software.
1256 The gamma encoding will be removed by libpng and the
1257 linear component values will be pre-multiplied by the
1260 With this format the final image must be re-encoded to
1261 match the display gamma before the image is displayed.
1262 If your system doesn't do that, yet still seems to
1263 perform arithmetic on the pixels without decoding them,
1264 it is broken - check out the modes below.
1266 With PNG_ALPHA_STANDARD libpng always produces linear
1267 component values, whatever screen_gamma you supply. The
1268 screen_gamma value is, however, used as a default for
1269 the file gamma if the PNG file has no gamma information.
1271 If you call png_set_gamma() after png_set_alpha_mode() you
1272 will override the linear encoding. Instead the
1273 pre-multiplied pixel values will be gamma encoded but
1274 the alpha channel will still be linear. This may
1275 actually match the requirements of some broken software,
1278 While linear 8-bit data is often used it has
1279 insufficient precision for any image with a reasonable
1280 dynamic range. To avoid problems, and if your software
1281 supports it, use png_set_expand_16() to force all
1282 components to 16 bits.
1284 PNG_ALPHA_OPTIMIZED: This mode is the same
1285 as PNG_ALPHA_STANDARD except that
1286 completely opaque pixels are gamma encoded according to
1287 the screen_gamma value. Pixels with alpha less than 1.0
1288 will still have linear components.
1290 Use this format if you have control over your
1291 compositing software and so don't do other arithmetic
1292 (such as scaling) on the data you get from libpng. Your
1293 compositing software can simply copy opaque pixels to
1294 the output but still has linear values for the
1297 In normal compositing, where the alpha channel encodes
1298 partial pixel coverage (as opposed to broad area
1299 translucency), the inaccuracies of the 8-bit
1300 representation of non-opaque pixels are irrelevant.
1302 You can also try this format if your software is broken;
1303 it might look better.
1305 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
1306 however, all component values,
1307 including the alpha channel are gamma encoded. This is
1308 an appropriate format to try if your software, or more
1309 likely hardware, is totally broken, i.e., if it performs
1310 linear arithmetic directly on gamma encoded values.
1312 In most cases of broken software or hardware the bug in the final display
1313 manifests as a subtle halo around composited parts of the image. You may not
1314 even perceive this as a halo; the composited part of the image may simply appear
1315 separate from the background, as though it had been cut out of paper and pasted
1318 If you don't have to deal with bugs in software or hardware, or if you can fix
1319 them, there are three recommended ways of using png_set_alpha_mode():
1321 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1324 You can do color correction on the result (libpng does not currently
1325 support color correction internally). When you handle the alpha channel
1326 you need to undo the gamma encoding and multiply out the alpha.
1328 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1330 png_set_expand_16(png_ptr);
1332 If you are using the high level interface, don't call png_set_expand_16();
1333 instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1335 With this mode you can't do color correction, but you can do arithmetic,
1336 including composition and scaling, on the data without further processing.
1338 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1341 You can avoid the expansion to 16-bit components with this mode, but you
1342 lose the ability to scale the image or perform other linear arithmetic.
1343 All you can do is compose the result onto a matching output. Since this
1344 mode is libpng-specific you also need to write your own composition
1347 If you don't need, or can't handle, the alpha channel you can call
1348 png_set_background() to remove it by compositing against a fixed color. Don't
1349 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1350 transparent parts of this image.
1352 png_set_background(png_ptr, &background_color,
1353 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1355 The background_color is an RGB or grayscale value according to the data format
1356 libpng will produce for you. Because you don't yet know the format of the PNG
1357 file, if you call png_set_background at this point you must arrange for the
1358 format produced by libpng to always have 8-bit or 16-bit components and then
1359 store the color as an 8-bit or 16-bit color as appropriate. The color contains
1360 separate gray and RGB component values, so you can let libpng produce gray or
1361 RGB output according to the input format, but low bit depth grayscale images
1362 must always be converted to at least 8-bit format. (Even though low bit depth
1363 grayscale images can't have an alpha channel they can have a transparent
1366 You set the transforms you need later, either as flags to the high level
1367 interface or libpng API calls for the low level interface. For reference the
1368 settings and API calls required are:
1371 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1372 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1374 If you must get exactly the same inaccurate results
1375 produced by default in versions prior to libpng-1.5.4,
1376 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1380 PNG_TRANSFORM_EXPAND_16
1381 png_set_expand_16(png_ptr);
1383 In either case palette image data will be expanded to RGB. If you just want
1384 color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1387 Calling png_set_background before the PNG file header is read will not work
1388 prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1389 errors it is therefore much safer to call png_set_background after the head has
1390 been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1391 used with the high level interface.
1393 .SS The high-level read interface
1395 At this point there are two ways to proceed; through the high-level
1396 read interface, or through a sequence of low-level read operations.
1397 You can use the high-level interface if (a) you are willing to read
1398 the entire image into memory, and (b) the input transformations
1399 you want to do are limited to the following set:
1401 PNG_TRANSFORM_IDENTITY No transformation
1402 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1404 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1405 8-bit less accurately
1406 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1407 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1409 PNG_TRANSFORM_PACKSWAP Change order of packed
1411 PNG_TRANSFORM_EXPAND Perform set_expand()
1412 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1413 PNG_TRANSFORM_SHIFT Normalize pixels to the
1415 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1417 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1419 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1421 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1422 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1423 to RGB (or GA to RGBA)
1424 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1426 (This excludes setting a background color, doing gamma transformation,
1427 quantizing, and setting filler.) If this is the case, simply do this:
1429 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1431 where png_transforms is an integer containing the bitwise OR of some
1432 set of transformation flags. This call is equivalent to png_read_info(),
1433 followed the set of transformations indicated by the transform mask,
1434 then png_read_image(), and finally png_read_end().
1436 (The final parameter of this call is not yet used. Someday it might point
1437 to transformation parameters required by some future input transform.)
1439 You must use png_transforms and not call any png_set_transform() functions
1440 when you use png_read_png().
1442 After you have called png_read_png(), you can retrieve the image data
1445 row_pointers = png_get_rows(png_ptr, info_ptr);
1447 where row_pointers is an array of pointers to the pixel data for each row:
1449 png_bytep row_pointers[height];
1451 If you know your image size and pixel size ahead of time, you can allocate
1452 row_pointers prior to calling png_read_png() with
1454 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1456 "Image is too tall to process in memory");
1458 if (width > PNG_UINT_32_MAX/pixel_size)
1460 "Image is too wide to process in memory");
1462 row_pointers = png_malloc(png_ptr,
1463 height*png_sizeof(png_bytep));
1465 for (int i=0; i<height, i++)
1466 row_pointers[i]=NULL; /* security precaution */
1468 for (int i=0; i<height, i++)
1469 row_pointers[i]=png_malloc(png_ptr,
1472 png_set_rows(png_ptr, info_ptr, &row_pointers);
1474 Alternatively you could allocate your image in one big block and define
1475 row_pointers[i] to point into the proper places in your block.
1477 If you use png_set_rows(), the application is responsible for freeing
1478 row_pointers (and row_pointers[i], if they were separately allocated).
1480 If you don't allocate row_pointers ahead of time, png_read_png() will
1481 do it, and it'll be free'ed by libpng when you call png_destroy_*().
1483 .SS The low-level read interface
1485 If you are going the low-level route, you are now ready to read all
1486 the file information up to the actual image data. You do this with a
1487 call to png_read_info().
1489 png_read_info(png_ptr, info_ptr);
1491 This will process all chunks up to but not including the image data.
1493 This also copies some of the data from the PNG file into the decode structure
1494 for use in later transformations. Important information copied in is:
1496 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
1497 provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1499 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1500 damages the information provided by an earlier call to png_set_background
1501 resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1503 3) The number of significant bits in each component value. Libpng uses this to
1504 optimize gamma handling by reducing the internal lookup table sizes.
1506 4) The transparent color information from a tRNS chunk. This can be modified by
1507 a later call to png_set_tRNS.
1509 .SS Querying the info structure
1511 Functions are used to get the information from the info_ptr once it
1512 has been read. Note that these fields may not be completely filled
1513 in until png_read_end() has read the chunk data following the image.
1515 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1516 &bit_depth, &color_type, &interlace_type,
1517 &compression_type, &filter_method);
1519 width - holds the width of the image
1520 in pixels (up to 2^31).
1522 height - holds the height of the image
1523 in pixels (up to 2^31).
1525 bit_depth - holds the bit depth of one of the
1526 image channels. (valid values are
1527 1, 2, 4, 8, 16 and depend also on
1528 the color_type. See also
1529 significant bits (sBIT) below).
1531 color_type - describes which color/alpha channels
1534 (bit depths 1, 2, 4, 8, 16)
1535 PNG_COLOR_TYPE_GRAY_ALPHA
1537 PNG_COLOR_TYPE_PALETTE
1538 (bit depths 1, 2, 4, 8)
1541 PNG_COLOR_TYPE_RGB_ALPHA
1544 PNG_COLOR_MASK_PALETTE
1545 PNG_COLOR_MASK_COLOR
1546 PNG_COLOR_MASK_ALPHA
1548 interlace_type - (PNG_INTERLACE_NONE or
1549 PNG_INTERLACE_ADAM7)
1551 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1554 filter_method - (must be PNG_FILTER_TYPE_BASE
1555 for PNG 1.0, and can also be
1556 PNG_INTRAPIXEL_DIFFERENCING if
1557 the PNG datastream is embedded in
1558 a MNG-1.0 datastream)
1560 Any or all of interlace_type, compression_type, or
1561 filter_method can be NULL if you are
1562 not interested in their values.
1564 Note that png_get_IHDR() returns 32-bit data into
1565 the application's width and height variables.
1566 This is an unsafe situation if these are 16-bit
1567 variables. In such situations, the
1568 png_get_image_width() and png_get_image_height()
1569 functions described below are safer.
1571 width = png_get_image_width(png_ptr,
1574 height = png_get_image_height(png_ptr,
1577 bit_depth = png_get_bit_depth(png_ptr,
1580 color_type = png_get_color_type(png_ptr,
1583 interlace_type = png_get_interlace_type(png_ptr,
1586 compression_type = png_get_compression_type(png_ptr,
1589 filter_method = png_get_filter_type(png_ptr,
1592 channels = png_get_channels(png_ptr, info_ptr);
1594 channels - number of channels of info for the
1595 color type (valid values are 1 (GRAY,
1596 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1597 4 (RGB_ALPHA or RGB + filler byte))
1599 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1601 rowbytes - number of bytes needed to hold a row
1603 signature = png_get_signature(png_ptr, info_ptr);
1605 signature - holds the signature read from the
1606 file (if any). The data is kept in
1607 the same offset it would be if the
1608 whole signature were read (i.e. if an
1609 application had already read in 4
1610 bytes of signature before starting
1611 libpng, the remaining 4 bytes would
1612 be in signature[4] through signature[7]
1613 (see png_set_sig_bytes())).
1615 These are also important, but their validity depends on whether the chunk
1616 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1617 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1618 data has been read, or zero if it is missing. The parameters to the
1619 png_get_<chunk> are set directly if they are simple data types, or a
1620 pointer into the info_ptr is returned for any complex types.
1622 The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
1623 is simply returned to give the application information about how the
1624 image was encoded. Libpng itself only does transformations using the file
1625 gamma when combining semitransparent pixels with the background color.
1627 png_get_PLTE(png_ptr, info_ptr, &palette,
1630 palette - the palette for the file
1631 (array of png_color)
1633 num_palette - number of entries in the palette
1635 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1636 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1638 file_gamma - the gamma at which the file was
1639 written (PNG_INFO_gAMA)
1641 int_file_gamma - 100,000 times the gamma at which the
1644 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
1645 &red_y, &green_x, &green_y, &blue_x, &blue_y)
1646 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X,
1647 &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z)
1648 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y,
1649 &int_red_x, &int_red_y, &int_green_x, &int_green_y,
1650 &int_blue_x, &int_blue_y)
1651 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
1652 &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z,
1653 &int_blue_X, &int_blue_Y, &int_blue_Z)
1655 {white,red,green,blue}_{x,y}
1656 A color space encoding specified using the
1657 chromaticities of the end points and the
1658 white point. (PNG_INFO_cHRM)
1660 {red,green,blue}_{X,Y,Z}
1661 A color space encoding specified using the encoding end
1662 points - the CIE tristimulus specification of the intended
1663 color of the red, green and blue channels in the PNG RGB
1664 data. The white point is simply the sum of the three end
1665 points. (PNG_INFO_cHRM)
1667 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1669 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
1670 The presence of the sRGB chunk
1671 means that the pixel data is in the
1672 sRGB color space. This chunk also
1673 implies specific values of gAMA and
1676 png_get_iCCP(png_ptr, info_ptr, &name,
1677 &compression_type, &profile, &proflen);
1679 name - The profile name.
1681 compression_type - The compression type; always
1682 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1683 You may give NULL to this argument to
1686 profile - International Color Consortium color
1687 profile data. May contain NULs.
1689 proflen - length of profile data in bytes.
1691 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1693 sig_bit - the number of significant bits for
1694 (PNG_INFO_sBIT) each of the gray,
1695 red, green, and blue channels,
1696 whichever are appropriate for the
1697 given color type (png_color_16)
1699 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1700 &num_trans, &trans_color);
1702 trans_alpha - array of alpha (transparency)
1703 entries for palette (PNG_INFO_tRNS)
1705 num_trans - number of transparent entries
1708 trans_color - graylevel or color sample values of
1709 the single transparent color for
1710 non-paletted images (PNG_INFO_tRNS)
1712 png_get_hIST(png_ptr, info_ptr, &hist);
1715 hist - histogram of palette (array of
1718 png_get_tIME(png_ptr, info_ptr, &mod_time);
1720 mod_time - time image was last modified
1723 png_get_bKGD(png_ptr, info_ptr, &background);
1725 background - background color (of type
1726 png_color_16p) (PNG_VALID_bKGD)
1727 valid 16-bit red, green and blue
1728 values, regardless of color_type
1730 num_comments = png_get_text(png_ptr, info_ptr,
1731 &text_ptr, &num_text);
1733 num_comments - number of comments
1735 text_ptr - array of png_text holding image
1738 text_ptr[i].compression - type of compression used
1739 on "text" PNG_TEXT_COMPRESSION_NONE
1740 PNG_TEXT_COMPRESSION_zTXt
1741 PNG_ITXT_COMPRESSION_NONE
1742 PNG_ITXT_COMPRESSION_zTXt
1744 text_ptr[i].key - keyword for comment. Must contain
1747 text_ptr[i].text - text comments for current
1748 keyword. Can be empty.
1750 text_ptr[i].text_length - length of text string,
1751 after decompression, 0 for iTXt
1753 text_ptr[i].itxt_length - length of itxt string,
1754 after decompression, 0 for tEXt/zTXt
1756 text_ptr[i].lang - language of comment (empty
1757 string for unknown).
1759 text_ptr[i].lang_key - keyword in UTF-8
1760 (empty string for unknown).
1762 Note that the itxt_length, lang, and lang_key
1763 members of the text_ptr structure only exist when the
1764 library is built with iTXt chunk support. Prior to
1765 libpng-1.4.0 the library was built by default without
1766 iTXt support. Also note that when iTXt is supported,
1767 they contain NULL pointers when the "compression"
1768 field contains PNG_TEXT_COMPRESSION_NONE or
1769 PNG_TEXT_COMPRESSION_zTXt.
1771 num_text - number of comments (same as
1772 num_comments; you can put NULL here
1773 to avoid the duplication)
1775 Note while png_set_text() will accept text, language,
1776 and translated keywords that can be NULL pointers, the
1777 structure returned by png_get_text will always contain
1778 regular zero-terminated C strings. They might be
1779 empty strings but they will never be NULL pointers.
1781 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1784 num_spalettes - number of sPLT chunks read.
1786 palette_ptr - array of palette structures holding
1787 contents of one or more sPLT chunks
1790 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1793 offset_x - positive offset from the left edge
1794 of the screen (can be negative)
1796 offset_y - positive offset from the top edge
1797 of the screen (can be negative)
1799 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1801 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1804 res_x - pixels/unit physical resolution in
1807 res_y - pixels/unit physical resolution in
1810 unit_type - PNG_RESOLUTION_UNKNOWN,
1811 PNG_RESOLUTION_METER
1813 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1816 unit - physical scale units (an integer)
1818 width - width of a pixel in physical scale units
1820 height - height of a pixel in physical scale units
1821 (width and height are doubles)
1823 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1826 unit - physical scale units (an integer)
1828 width - width of a pixel in physical scale units
1829 (expressed as a string)
1831 height - height of a pixel in physical scale units
1832 (width and height are strings like "2.54")
1834 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1835 info_ptr, &unknowns)
1837 unknowns - array of png_unknown_chunk
1838 structures holding unknown chunks
1840 unknowns[i].name - name of unknown chunk
1842 unknowns[i].data - data of unknown chunk
1844 unknowns[i].size - size of unknown chunk's data
1846 unknowns[i].location - position of chunk in file
1848 The value of "i" corresponds to the order in which the
1849 chunks were read from the PNG file or inserted with the
1850 png_set_unknown_chunks() function.
1852 The value of "location" is a bitwise "or" of
1854 PNG_HAVE_IHDR (0x01)
1855 PNG_HAVE_PLTE (0x02)
1856 PNG_AFTER_IDAT (0x08)
1858 The data from the pHYs chunk can be retrieved in several convenient
1861 res_x = png_get_x_pixels_per_meter(png_ptr,
1864 res_y = png_get_y_pixels_per_meter(png_ptr,
1867 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1870 res_x = png_get_x_pixels_per_inch(png_ptr,
1873 res_y = png_get_y_pixels_per_inch(png_ptr,
1876 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1879 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1882 Each of these returns 0 [signifying "unknown"] if
1883 the data is not present or if res_x is 0;
1884 res_x_and_y is 0 if res_x != res_y
1886 Note that because of the way the resolutions are
1887 stored internally, the inch conversions won't
1888 come out to exactly even number. For example,
1889 72 dpi is stored as 0.28346 pixels/meter, and
1890 when this is retrieved it is 71.9988 dpi, so
1891 be sure to round the returned value appropriately
1892 if you want to display a reasonable-looking result.
1894 The data from the oFFs chunk can be retrieved in several convenient
1897 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1899 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1901 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1903 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1905 Each of these returns 0 [signifying "unknown" if both
1906 x and y are 0] if the data is not present or if the
1907 chunk is present but the unit is the pixel. The
1908 remark about inexact inch conversions applies here
1909 as well, because a value in inches can't always be
1910 converted to microns and back without some loss
1913 For more information, see the
1914 PNG specification for chunk contents. Be careful with trusting
1915 rowbytes, as some of the transformations could increase the space
1916 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1917 See png_read_update_info(), below.
1919 A quick word about text_ptr and num_text. PNG stores comments in
1920 keyword/text pairs, one pair per chunk, with no limit on the number
1921 of text chunks, and a 2^31 byte limit on their size. While there are
1922 suggested keywords, there is no requirement to restrict the use to these
1923 strings. It is strongly suggested that keywords and text be sensible
1924 to humans (that's the point), so don't use abbreviations. Non-printing
1925 symbols are not allowed. See the PNG specification for more details.
1926 There is also no requirement to have text after the keyword.
1928 Keywords should be limited to 79 Latin-1 characters without leading or
1929 trailing spaces, but non-consecutive spaces are allowed within the
1930 keyword. It is possible to have the same keyword any number of times.
1931 The text_ptr is an array of png_text structures, each holding a
1932 pointer to a language string, a pointer to a keyword and a pointer to
1933 a text string. The text string, language code, and translated
1934 keyword may be empty or NULL pointers. The keyword/text
1935 pairs are put into the array in the order that they are received.
1936 However, some or all of the text chunks may be after the image, so, to
1937 make sure you have read all the text chunks, don't mess with these
1938 until after you read the stuff after the image. This will be
1939 mentioned again below in the discussion that goes with png_read_end().
1941 .SS Input transformations
1943 After you've read the header information, you can set up the library
1944 to handle any special transformations of the image data. The various
1945 ways to transform the data will be described in the order that they
1946 should occur. This is important, as some of these change the color
1947 type and/or bit depth of the data, and some others only work on
1948 certain color types and bit depths.
1950 Transformations you request are ignored if they don't have any meaning for a
1951 particular input data format. However some transformations can have an effect
1952 as a result of a previous transformation. If you specify a contradictory set of
1953 transformations, for example both adding and removing the alpha channel, you
1954 cannot predict the final result.
1956 The color used for the transparency values should be supplied in the same
1957 format/depth as the current image data. It is stored in the same format/depth
1958 as the image data in a tRNS chunk, so this is what libpng expects for this data.
1960 The color used for the background value depends on the need_expand argument as
1963 Data will be decoded into the supplied row buffers packed into bytes
1964 unless the library has been told to transform it into another format.
1965 For example, 4 bit/pixel paletted or grayscale data will be returned
1966 2 pixels/byte with the leftmost pixel in the high-order bits of the
1967 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1968 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1969 is called to insert filler bytes, either before or after each RGB triplet.
1970 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1971 byte of the color value first, unless png_set_scale_16() is called to
1972 transform it to regular RGB RGB triplets, or png_set_filler() or
1973 png_set_add alpha() is called to insert filler bytes, either before or
1974 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1975 be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
1976 or png_set_scale_16().
1978 The following code transforms grayscale images of less than 8 to 8 bits,
1979 changes paletted images to RGB, and adds a full alpha channel if there is
1980 transparency information in a tRNS chunk. This is most useful on
1981 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1982 viewing application that wishes to treat all images in the same way.
1984 if (color_type == PNG_COLOR_TYPE_PALETTE)
1985 png_set_palette_to_rgb(png_ptr);
1987 if (png_get_valid(png_ptr, info_ptr,
1988 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1990 if (color_type == PNG_COLOR_TYPE_GRAY &&
1991 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1993 The first two functions are actually aliases for png_set_expand(), added
1994 in libpng version 1.0.4, with the function names expanded to improve code
1995 readability. In some future version they may actually do different
1998 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1999 added. It expands the sample depth without changing tRNS to alpha.
2001 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2002 png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2003 Use this when the output color or gray channels are made linear to avoid fairly
2004 severe accuracy loss.
2007 png_set_expand_16(png_ptr);
2009 PNG can have files with 16 bits per channel. If you only can handle
2010 8 bits per channel, this will strip the pixels down to 8-bit.
2012 if (bit_depth == 16)
2013 #if PNG_LIBPNG_VER >= 10504
2014 png_set_scale_16(png_ptr);
2016 png_set_strip_16(png_ptr);
2019 (The more accurate "png_set_scale_16()" API became available in libpng version
2022 If you need to process the alpha channel on the image separately from the image
2023 data (for example if you convert it to a bitmap mask) it is possible to have
2024 libpng strip the channel leaving just RGB or gray data:
2026 if (color_type & PNG_COLOR_MASK_ALPHA)
2027 png_set_strip_alpha(png_ptr);
2029 If you strip the alpha channel you need to find some other way of dealing with
2030 the information. If, instead, you want to convert the image to an opaque
2031 version with no alpha channel use png_set_background; see below.
2033 As of libpng version 1.5.2, almost all useful expansions are supported, the
2034 major ommissions are conversion of grayscale to indexed images (which can be
2035 done trivially in the application) and conversion of indexed to grayscale (which
2036 can be done by a trivial manipulation of the palette.)
2038 In the following table, the 01 means grayscale with depth<8, 31 means
2039 indexed with depth<8, other numerals represent the color type, "T" means
2040 the tRNS chunk is present, A means an alpha channel is present, and O
2041 means tRNS or alpha is present but all pixels in the image are opaque.
2043 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2045 01 - [G] - - - - - - - - - - - - -
2046 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2047 0 1 G + . . G G G G G G B B GB GB
2048 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2049 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2050 2 C P C C C + . . C - - CB CB B B
2051 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2052 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2053 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2054 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2055 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2056 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2057 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2058 6A CA PA CA C C A T tT PA P P C CBA + BA
2059 6O CA PBA CA C C A tT T PA P P CBA C BA +
2062 "+" identifies entries where 'from' and 'to' are the same.
2063 "-" means the transformation is not supported.
2064 "." means nothing is necessary (a tRNS chunk can just be ignored).
2065 "t" means the transformation is obtained by png_set_tRNS.
2066 "A" means the transformation is obtained by png_set_add_alpha().
2067 "X" means the transformation is obtained by png_set_expand().
2068 "1" means the transformation is obtained by
2069 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
2070 if there is no transparency in the original or the final
2072 "C" means the transformation is obtained by png_set_gray_to_rgb().
2073 "G" means the transformation is obtained by png_set_rgb_to_gray().
2074 "P" means the transformation is obtained by
2075 png_set_expand_palette_to_rgb().
2076 "p" means the transformation is obtained by png_set_packing().
2077 "Q" means the transformation is obtained by png_set_quantize().
2078 "T" means the transformation is obtained by
2079 png_set_tRNS_to_alpha().
2080 "B" means the transformation is obtained by
2081 png_set_background(), or png_strip_alpha().
2083 When an entry has multiple transforms listed all are required to cause the
2084 right overall transformation. When two transforms are separated by a comma
2085 either will do the job. When transforms are enclosed in [] the transform should
2086 do the job but this is currently unimplemented - a different format will result
2087 if the suggested transformations are used.
2089 In PNG files, the alpha channel in an image
2090 is the level of opacity. If you need the alpha channel in an image to
2091 be the level of transparency instead of opacity, you can invert the
2092 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2093 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2094 images) is fully transparent, with
2096 png_set_invert_alpha(png_ptr);
2098 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2099 they can, resulting in, for example, 8 pixels per byte for 1 bit
2100 files. This code expands to 1 pixel per byte without changing the
2101 values of the pixels:
2104 png_set_packing(png_ptr);
2106 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2107 stored in a PNG image have been "scaled" or "shifted" up to the next
2108 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2109 to 8 bits/sample in the range [0, 255]). However, it is also possible
2110 to convert the PNG pixel data back to the original bit depth of the
2111 image. This call reduces the pixels back down to the original bit depth:
2113 png_color_8p sig_bit;
2115 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2116 png_set_shift(png_ptr, sig_bit);
2118 PNG files store 3-color pixels in red, green, blue order. This code
2119 changes the storage of the pixels to blue, green, red:
2121 if (color_type == PNG_COLOR_TYPE_RGB ||
2122 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2123 png_set_bgr(png_ptr);
2125 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2126 into 4 or 8 bytes for windowing systems that need them in this format:
2128 if (color_type == PNG_COLOR_TYPE_RGB)
2129 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2131 where "filler" is the 8 or 16-bit number to fill with, and the location is
2132 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2133 you want the filler before the RGB or after. This transformation
2134 does not affect images that already have full alpha channels. To add an
2135 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2136 will generate RGBA pixels.
2138 Note that png_set_filler() does not change the color type. If you want
2139 to do that, you can add a true alpha channel with
2141 if (color_type == PNG_COLOR_TYPE_RGB ||
2142 color_type == PNG_COLOR_TYPE_GRAY)
2143 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2145 where "filler" contains the alpha value to assign to each pixel.
2146 This function was added in libpng-1.2.7.
2148 If you are reading an image with an alpha channel, and you need the
2149 data as ARGB instead of the normal PNG format RGBA:
2151 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2152 png_set_swap_alpha(png_ptr);
2154 For some uses, you may want a grayscale image to be represented as
2155 RGB. This code will do that conversion:
2157 if (color_type == PNG_COLOR_TYPE_GRAY ||
2158 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2159 png_set_gray_to_rgb(png_ptr);
2161 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2164 if (color_type == PNG_COLOR_TYPE_RGB ||
2165 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2166 png_set_rgb_to_gray(png_ptr, error_action,
2167 double red_weight, double green_weight);
2169 error_action = 1: silently do the conversion
2171 error_action = 2: issue a warning if the original
2172 image has any pixel where
2173 red != green or red != blue
2175 error_action = 3: issue an error and abort the
2176 conversion if the original
2177 image has any pixel where
2178 red != green or red != blue
2180 red_weight: weight of red component
2182 green_weight: weight of green component
2183 If either weight is negative, default
2186 In the corresponding fixed point API the red_weight and green_weight values are
2187 simply scaled by 100,000:
2189 png_set_rgb_to_gray(png_ptr, error_action,
2190 png_fixed_point red_weight,
2191 png_fixed_point green_weight);
2193 If you have set error_action = 1 or 2, you can
2194 later check whether the image really was gray, after processing
2195 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2196 It will return a png_byte that is zero if the image was gray or
2197 1 if there were any non-gray pixels. Background and sBIT data
2198 will be silently converted to grayscale, using the green channel
2199 data for sBIT, regardless of the error_action setting.
2201 The default values come from the PNG file cHRM chunk if present; otherwise, the
2202 defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2203 space, as recommended in the Charles Poynton's Colour FAQ,
2204 <http://www.poynton.com/>, in section 9:
2206 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2208 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2210 Previous versions of this document, 1998 through 2002, recommended a slightly
2213 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2215 Libpng uses an integer approximation:
2217 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2219 The calculation is done in a linear colorspace, if the image gamma
2222 The png_set_background() function has been described already; it tells libpng to
2223 composite images with alpha or simple transparency against the supplied
2224 background color. For compatibility with versions of libpng earlier than
2225 libpng-1.5.4 it is recommended that you call the function after reading the file
2226 header, even if you don't want to use the color in a bKGD chunk, if one exists.
2228 If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2229 you may use this color, or supply another color more suitable for
2230 the current display (e.g., the background color from a web page). You
2231 need to tell libpng how the color is represented, both the format of the
2232 component values in the color (the number of bits) and the gamma encoding of the
2233 color. The function takes two arguments, background_gamma_mode and need_expand
2234 to convey this information; however, only two combinations are likely to be
2237 png_color_16 my_background;
2238 png_color_16p image_background;
2240 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2241 png_set_background(png_ptr, image_background,
2242 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2244 png_set_background(png_ptr, &my_background,
2245 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2247 The second call was described above - my_background is in the format of the
2248 final, display, output produced by libpng. Because you now know the format of
2249 the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2250 output and to retain palette images (the palette colors will be modified
2251 appropriately and the tRNS chunk removed.) However, if you are doing this,
2252 take great care not to ask for transformations without checking first that
2255 In the first call the background color has the original bit depth and color type
2256 of the PNG file. So, for palette images the color is supplied as a palette
2257 index and for low bit greyscale images the color is a reduced bit value in
2258 image_background->gray.
2260 If you didn't call png_set_gamma() before reading the file header, for example
2261 if you need your code to remain compatible with older versions of libpng prior
2262 to libpng-1.5.4, this is the place to call it.
2264 Do not call it if you called png_set_alpha_mode(); doing so will damage the
2265 settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2266 supported then you can certainly do png_set_gamma() before reading the PNG
2269 This API unconditionally sets the screen and file gamma values, so it will
2270 override the value in the PNG file unless it is called before the PNG file
2271 reading starts. For this reason you must always call it with the PNG file
2272 value when you call it in this position:
2274 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2275 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2278 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2280 If you need to reduce an RGB file to a paletted file, or if a paletted
2281 file has more entries then will fit on your screen, png_set_quantize()
2282 will do that. Note that this is a simple match quantization that merely
2283 finds the closest color available. This should work fairly well with
2284 optimized palettes, but fairly badly with linear color cubes. If you
2285 pass a palette that is larger than maximum_colors, the file will
2286 reduce the number of colors in the palette so it will fit into
2287 maximum_colors. If there is a histogram, libpng will use it to make
2288 more intelligent choices when reducing the palette. If there is no
2289 histogram, it may not do as good a job.
2291 if (color_type & PNG_COLOR_MASK_COLOR)
2293 if (png_get_valid(png_ptr, info_ptr,
2296 png_uint_16p histogram = NULL;
2298 png_get_hIST(png_ptr, info_ptr,
2300 png_set_quantize(png_ptr, palette, num_palette,
2301 max_screen_colors, histogram, 1);
2306 png_color std_color_cube[MAX_SCREEN_COLORS] =
2309 png_set_quantize(png_ptr, std_color_cube,
2310 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2315 PNG files describe monochrome as black being zero and white being one.
2316 The following code will reverse this (make black be one and white be
2319 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2320 png_set_invert_mono(png_ptr);
2322 This function can also be used to invert grayscale and gray-alpha images:
2324 if (color_type == PNG_COLOR_TYPE_GRAY ||
2325 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2326 png_set_invert_mono(png_ptr);
2328 PNG files store 16-bit pixels in network byte order (big-endian,
2329 ie. most significant bits first). This code changes the storage to the
2330 other way (little-endian, i.e. least significant bits first, the
2331 way PCs store them):
2333 if (bit_depth == 16)
2334 png_set_swap(png_ptr);
2336 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2337 need to change the order the pixels are packed into bytes, you can use:
2340 png_set_packswap(png_ptr);
2342 Finally, you can write your own transformation function if none of
2343 the existing ones meets your needs. This is done by setting a callback
2346 png_set_read_user_transform_fn(png_ptr,
2349 You must supply the function
2351 void read_transform_fn(png_structp png_ptr, png_row_infop
2352 row_info, png_bytep data)
2354 See pngtest.c for a working example. Your function will be called
2355 after all of the other transformations have been processed. Take care with
2356 interlaced images if you do the interlace yourself - the width of the row is the
2357 width in 'row_info', not the overall image width.
2359 If supported, libpng provides two information routines that you can use to find
2360 where you are in processing the image:
2362 png_get_current_pass_number(png_structp png_ptr);
2363 png_get_current_row_number(png_structp png_ptr);
2365 Don't try using these outside a transform callback - firstly they are only
2366 supported if user transforms are supported, secondly they may well return
2367 unexpected results unless the row is actually being processed at the moment they
2371 images the value returned is the row in the input sub-image image. Use
2372 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2373 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2375 The discussion of interlace handling above contains more information on how to
2378 You can also set up a pointer to a user structure for use by your
2379 callback function, and you can inform libpng that your transform
2380 function will change the number of channels or bit depth with the
2383 png_set_user_transform_info(png_ptr, user_ptr,
2384 user_depth, user_channels);
2386 The user's application, not libpng, is responsible for allocating and
2387 freeing any memory required for the user structure.
2389 You can retrieve the pointer via the function
2390 png_get_user_transform_ptr(). For example:
2392 voidp read_user_transform_ptr =
2393 png_get_user_transform_ptr(png_ptr);
2395 The last thing to handle is interlacing; this is covered in detail below,
2396 but you must call the function here if you want libpng to handle expansion
2397 of the interlaced image.
2399 number_of_passes = png_set_interlace_handling(png_ptr);
2401 After setting the transformations, libpng can update your png_info
2402 structure to reflect any transformations you've requested with this
2405 png_read_update_info(png_ptr, info_ptr);
2407 This is most useful to update the info structure's rowbytes
2408 field so you can use it to allocate your image memory. This function
2409 will also update your palette with the correct screen_gamma and
2410 background if these have been given with the calls above. You may
2411 only call png_read_update_info() once with a particular info_ptr.
2413 After you call png_read_update_info(), you can allocate any
2414 memory you need to hold the image. The row data is simply
2415 raw byte data for all forms of images. As the actual allocation
2416 varies among applications, no example will be given. If you
2417 are allocating one large chunk, you will need to build an
2418 array of pointers to each row, as it will be needed for some
2419 of the functions below.
2421 Remember: Before you call png_read_update_info(), the png_get_*()
2422 functions return the values corresponding to the original PNG image.
2423 After you call png_read_update_info the values refer to the image
2424 that libpng will output. Consequently you must call all the png_set_
2425 functions before you call png_read_update_info(). This is particularly
2426 important for png_set_interlace_handling() - if you are going to call
2427 png_read_update_info() you must call png_set_interlace_handling() before
2428 it unless you want to receive interlaced output.
2430 .SS Reading image data
2432 After you've allocated memory, you can read the image data.
2433 The simplest way to do this is in one function call. If you are
2434 allocating enough memory to hold the whole image, you can just
2435 call png_read_image() and libpng will read in all the image data
2436 and put it in the memory area supplied. You will need to pass in
2437 an array of pointers to each row.
2439 This function automatically handles interlacing, so you don't
2440 need to call png_set_interlace_handling() (unless you call
2441 png_read_update_info()) or call this function multiple times, or any
2442 of that other stuff necessary with png_read_rows().
2444 png_read_image(png_ptr, row_pointers);
2446 where row_pointers is:
2448 png_bytep row_pointers[height];
2450 You can point to void or char or whatever you use for pixels.
2452 If you don't want to read in the whole image at once, you can
2453 use png_read_rows() instead. If there is no interlacing (check
2454 interlace_type == PNG_INTERLACE_NONE), this is simple:
2456 png_read_rows(png_ptr, row_pointers, NULL,
2459 where row_pointers is the same as in the png_read_image() call.
2461 If you are doing this just one row at a time, you can do this with
2462 a single row_pointer instead of an array of row_pointers:
2464 png_bytep row_pointer = row;
2465 png_read_row(png_ptr, row_pointer, NULL);
2467 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2468 get somewhat harder. The only current (PNG Specification version 1.2)
2469 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2470 a somewhat complicated 2D interlace scheme, known as Adam7, that
2471 breaks down an image into seven smaller images of varying size, based
2472 on an 8x8 grid. This number is defined (from libpng 1.5) as
2473 PNG_INTERLACE_ADAM7_PASSES in png.h
2475 libpng can fill out those images or it can give them to you "as is".
2476 It is almost always better to have libpng handle the interlacing for you.
2477 If you want the images filled out, there are two ways to do that. The one
2478 mentioned in the PNG specification is to expand each pixel to cover
2479 those pixels that have not been read yet (the "rectangle" method).
2480 This results in a blocky image for the first pass, which gradually
2481 smooths out as more pixels are read. The other method is the "sparkle"
2482 method, where pixels are drawn only in their final locations, with the
2483 rest of the image remaining whatever colors they were initialized to
2484 before the start of the read. The first method usually looks better,
2485 but tends to be slower, as there are more pixels to put in the rows.
2487 If, as is likely, you want libpng to expand the images, call this before
2488 calling png_start_read_image() or png_read_update_info():
2490 if (interlace_type == PNG_INTERLACE_ADAM7)
2492 = png_set_interlace_handling(png_ptr);
2494 This will return the number of passes needed. Currently, this is seven,
2495 but may change if another interlace type is added. This function can be
2496 called even if the file is not interlaced, where it will return one pass.
2497 You then need to read the whole image 'number_of_passes' times. Each time
2498 will distribute the pixels from the current pass to the correct place in
2499 the output image, so you need to supply the same rows to png_read_rows in
2502 If you are not going to display the image after each pass, but are
2503 going to wait until the entire image is read in, use the sparkle
2504 effect. This effect is faster and the end result of either method
2505 is exactly the same. If you are planning on displaying the image
2506 after each pass, the "rectangle" effect is generally considered the
2509 If you only want the "sparkle" effect, just call png_read_rows() as
2510 normal, with the third parameter NULL. Make sure you make pass over
2511 the image number_of_passes times, and you don't change the data in the
2512 rows between calls. You can change the locations of the data, just
2513 not the data. Each pass only writes the pixels appropriate for that
2514 pass, and assumes the data from previous passes is still valid.
2516 png_read_rows(png_ptr, row_pointers, NULL,
2519 If you only want the first effect (the rectangles), do the same as
2520 before except pass the row buffer in the third parameter, and leave
2521 the second parameter NULL.
2523 png_read_rows(png_ptr, NULL, row_pointers,
2526 If you don't want libpng to handle the interlacing details, just call
2527 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2528 Each of the images is a valid image by itself; however, you will almost
2529 certainly need to distribute the pixels from each sub-image to the
2530 correct place. This is where everything gets very tricky.
2532 If you want to retrieve the separate images you must pass the correct
2533 number of rows to each successive call of png_read_rows(). The calculation
2534 gets pretty complicated for small images, where some sub-images may
2535 not even exist because either their width or height ends up zero.
2536 libpng provides two macros to help you in 1.5 and later versions:
2538 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2539 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2541 Respectively these tell you the width and height of the sub-image
2542 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2543 this can be confusing because the specification refers to the same passes
2544 as 1 to 7! Be careful, you must check both the width and height before
2545 calling png_read_rows() and not call it for that pass if either is zero.
2547 You can, of course, read each sub-image row by row. If you want to
2548 produce optimal code to make a pixel-by-pixel transformation of an
2549 interlaced image this is the best approach; read each row of each pass,
2550 transform it, and write it out to a new interlaced image.
2552 If you want to de-interlace the image yourself libpng provides further
2553 macros to help that tell you where to place the pixels in the output image.
2554 Because the interlacing scheme is rectangular - sub-image pixels are always
2555 arranged on a rectangular grid - all you need to know for each pass is the
2556 starting column and row in the output image of the first pixel plus the
2557 spacing between each pixel. As of libpng 1.5 there are four macros to
2558 retrieve this information:
2560 png_uint_32 x = PNG_PASS_START_COL(pass);
2561 png_uint_32 y = PNG_PASS_START_ROW(pass);
2562 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2563 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2565 These allow you to write the obvious loop:
2567 png_uint_32 input_y = 0;
2568 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2570 while (output_y < output_image_height)
2572 png_uint_32 input_x = 0;
2573 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2575 while (output_x < output_image_width)
2577 image[output_y][output_x] =
2578 subimage[pass][input_y][input_x++];
2587 Notice that the steps between successive output rows and columns are
2588 returned as shifts. This is possible because the pixels in the subimages
2589 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2590 image. In practice you may need to directly calculate the output coordinate
2591 given an input coordinate. libpng provides two further macros for this
2594 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2595 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2597 Finally a pair of macros are provided to tell you if a particular image
2598 row or column appears in a given pass:
2600 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2601 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2603 Bear in mind that you will probably also need to check the width and height
2604 of the pass in addition to the above to be sure the pass even exists!
2606 With any luck you are convinced by now that you don't want to do your own
2607 interlace handling. In reality normally the only good reason for doing this
2608 is if you are processing PNG files on a pixel-by-pixel basis and don't want
2609 to load the whole file into memory when it is interlaced.
2611 libpng includes a test program, pngvalid, that illustrates reading and
2612 writing of interlaced images. If you can't get interlacing to work in your
2613 code and don't want to leave it to libpng (the recommended approach), see
2614 how pngvalid.c does it.
2616 .SS Finishing a sequential read
2618 After you are finished reading the image through the
2619 low-level interface, you can finish reading the file. If you are
2620 interested in comments or time, which may be stored either before or
2621 after the image data, you should pass the separate png_info struct if
2622 you want to keep the comments from before and after the image
2625 png_infop end_info = png_create_info_struct(png_ptr);
2629 png_destroy_read_struct(&png_ptr, &info_ptr,
2634 png_read_end(png_ptr, end_info);
2636 If you are not interested, you should still call png_read_end()
2637 but you can pass NULL, avoiding the need to create an end_info structure.
2639 png_read_end(png_ptr, (png_infop)NULL);
2641 If you don't call png_read_end(), then your file pointer will be
2642 left pointing to the first chunk after the last IDAT, which is probably
2643 not what you want if you expect to read something beyond the end of
2646 When you are done, you can free all memory allocated by libpng like this:
2648 png_destroy_read_struct(&png_ptr, &info_ptr,
2651 or, if you didn't create an end_info structure,
2653 png_destroy_read_struct(&png_ptr, &info_ptr,
2656 It is also possible to individually free the info_ptr members that
2657 point to libpng-allocated storage with the following function:
2659 png_free_data(png_ptr, info_ptr, mask, seq)
2661 mask - identifies data to be freed, a mask
2662 containing the bitwise OR of one or
2664 PNG_FREE_PLTE, PNG_FREE_TRNS,
2665 PNG_FREE_HIST, PNG_FREE_ICCP,
2666 PNG_FREE_PCAL, PNG_FREE_ROWS,
2667 PNG_FREE_SCAL, PNG_FREE_SPLT,
2668 PNG_FREE_TEXT, PNG_FREE_UNKN,
2669 or simply PNG_FREE_ALL
2671 seq - sequence number of item to be freed
2674 This function may be safely called when the relevant storage has
2675 already been freed, or has not yet been allocated, or was allocated
2676 by the user and not by libpng, and will in those cases do nothing.
2677 The "seq" parameter is ignored if only one item of the selected data
2678 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
2679 are allowed for the data type identified in the mask, such as text or
2680 sPLT, only the n'th item in the structure is freed, where n is "seq".
2682 The default behavior is only to free data that was allocated internally
2683 by libpng. This can be changed, so that libpng will not free the data,
2684 or so that it will free data that was allocated by the user with png_malloc()
2685 or png_calloc() and passed in via a png_set_*() function, with
2687 png_data_freer(png_ptr, info_ptr, freer, mask)
2690 PNG_DESTROY_WILL_FREE_DATA
2691 PNG_SET_WILL_FREE_DATA
2692 PNG_USER_WILL_FREE_DATA
2694 mask - which data elements are affected
2695 same choices as in png_free_data()
2697 This function only affects data that has already been allocated.
2698 You can call this function after reading the PNG data but before calling
2699 any png_set_*() functions, to control whether the user or the png_set_*()
2700 function is responsible for freeing any existing data that might be present,
2701 and again after the png_set_*() functions to control whether the user
2702 or png_destroy_*() is supposed to free the data. When the user assumes
2703 responsibility for libpng-allocated data, the application must use
2704 png_free() to free it, and when the user transfers responsibility to libpng
2705 for data that the user has allocated, the user must have used png_malloc()
2706 or png_calloc() to allocate it.
2708 If you allocated your row_pointers in a single block, as suggested above in
2709 the description of the high level read interface, you must not transfer
2710 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2711 because they would also try to free the individual row_pointers[i].
2713 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2714 separately, do not transfer responsibility for freeing text_ptr to libpng,
2715 because when libpng fills a png_text structure it combines these members with
2716 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2717 if you transfer responsibility for free'ing text_ptr from libpng to your
2718 application, your application must not separately free those members.
2720 The png_free_data() function will turn off the "valid" flag for anything
2721 it frees. If you need to turn the flag off for a chunk that was freed by
2722 your application instead of by libpng, you can use
2724 png_set_invalid(png_ptr, info_ptr, mask);
2726 mask - identifies the chunks to be made invalid,
2727 containing the bitwise OR of one or
2729 PNG_INFO_gAMA, PNG_INFO_sBIT,
2730 PNG_INFO_cHRM, PNG_INFO_PLTE,
2731 PNG_INFO_tRNS, PNG_INFO_bKGD,
2732 PNG_INFO_hIST, PNG_INFO_pHYs,
2733 PNG_INFO_oFFs, PNG_INFO_tIME,
2734 PNG_INFO_pCAL, PNG_INFO_sRGB,
2735 PNG_INFO_iCCP, PNG_INFO_sPLT,
2736 PNG_INFO_sCAL, PNG_INFO_IDAT
2738 For a more compact example of reading a PNG image, see the file example.c.
2740 .SS Reading PNG files progressively
2742 The progressive reader is slightly different then the non-progressive
2743 reader. Instead of calling png_read_info(), png_read_rows(), and
2744 png_read_end(), you make one call to png_process_data(), which calls
2745 callbacks when it has the info, a row, or the end of the image. You
2746 set up these callbacks with png_set_progressive_read_fn(). You don't
2747 have to worry about the input/output functions of libpng, as you are
2748 giving the library the data directly in png_process_data(). I will
2749 assume that you have read the section on reading PNG files above,
2750 so I will only highlight the differences (although I will show
2753 png_structp png_ptr;
2756 /* An example code fragment of how you would
2757 initialize the progressive reader in your
2760 initialize_png_reader()
2762 png_ptr = png_create_read_struct
2763 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2764 user_error_fn, user_warning_fn);
2769 info_ptr = png_create_info_struct(png_ptr);
2773 png_destroy_read_struct(&png_ptr,
2774 (png_infopp)NULL, (png_infopp)NULL);
2778 if (setjmp(png_jmpbuf(png_ptr)))
2780 png_destroy_read_struct(&png_ptr, &info_ptr,
2785 /* This one's new. You can provide functions
2786 to be called when the header info is valid,
2787 when each row is completed, and when the image
2788 is finished. If you aren't using all functions,
2789 you can specify NULL parameters. Even when all
2790 three functions are NULL, you need to call
2791 png_set_progressive_read_fn(). You can use
2792 any struct as the user_ptr (cast to a void pointer
2793 for the function call), and retrieve the pointer
2794 from inside the callbacks using the function
2796 png_get_progressive_ptr(png_ptr);
2798 which will return a void pointer, which you have
2799 to cast appropriately.
2801 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2802 info_callback, row_callback, end_callback);
2807 /* A code fragment that you call as you receive blocks
2810 process_data(png_bytep buffer, png_uint_32 length)
2812 if (setjmp(png_jmpbuf(png_ptr)))
2814 png_destroy_read_struct(&png_ptr, &info_ptr,
2819 /* This one's new also. Simply give it a chunk
2820 of data from the file stream (in order, of
2821 course). On machines with segmented memory
2822 models machines, don't give it any more than
2823 64K. The library seems to run fine with sizes
2824 of 4K. Although you can give it much less if
2825 necessary (I assume you can give it chunks of
2826 1 byte, I haven't tried less then 256 bytes
2827 yet). When this function returns, you may
2828 want to display any rows that were generated
2829 in the row callback if you don't already do
2832 png_process_data(png_ptr, info_ptr, buffer, length);
2834 /* At this point you can call png_process_data_skip if
2835 you want to handle data the library will skip yourself;
2836 it simply returns the number of bytes to skip (and stops
2837 libpng skipping that number of bytes on the next
2838 png_process_data call).
2842 /* This function is called (as set by
2843 png_set_progressive_read_fn() above) when enough data
2844 has been supplied so all of the header has been
2848 info_callback(png_structp png_ptr, png_infop info)
2850 /* Do any setup here, including setting any of
2851 the transformations mentioned in the Reading
2852 PNG files section. For now, you _must_ call
2853 either png_start_read_image() or
2854 png_read_update_info() after all the
2855 transformations are set (even if you don't set
2856 any). You may start getting rows before
2857 png_process_data() returns, so this is your
2858 last chance to prepare for that.
2860 This is where you turn on interlace handling,
2861 assuming you don't want to do it yourself.
2863 If you need to you can stop the processing of
2864 your original input data at this point by calling
2865 png_process_data_pause. This returns the number
2866 of unprocessed bytes from the last png_process_data
2867 call - it is up to you to ensure that the next call
2868 sees these bytes again. If you don't want to bother
2869 with this you can get libpng to cache the unread
2870 bytes by setting the 'save' parameter (see png.h) but
2871 then libpng will have to copy the data internally.
2875 /* This function is called when each row of image
2878 row_callback(png_structp png_ptr, png_bytep new_row,
2879 png_uint_32 row_num, int pass)
2881 /* If the image is interlaced, and you turned
2882 on the interlace handler, this function will
2883 be called for every row in every pass. Some
2884 of these rows will not be changed from the
2885 previous pass. When the row is not changed,
2886 the new_row variable will be NULL. The rows
2887 and passes are called in order, so you don't
2888 really need the row_num and pass, but I'm
2889 supplying them because it may make your life
2892 If you did not turn on interlace handling then
2893 the callback is called for each row of each
2894 sub-image when the image is interlaced. In this
2895 case 'row_num' is the row in the sub-image, not
2896 the row in the output image as it is in all other
2899 For the non-NULL rows of interlaced images when
2900 you have switched on libpng interlace handling,
2901 you must call png_progressive_combine_row()
2902 passing in the row and the old row. You can
2903 call this function for NULL rows (it will just
2904 return) and for non-interlaced images (it just
2905 does the memcpy for you) if it will make the
2906 code easier. Thus, you can just do this for
2907 all cases if you switch on interlace handling;
2910 png_progressive_combine_row(png_ptr, old_row,
2913 /* where old_row is what was displayed for
2914 previously for the row. Note that the first
2915 pass (pass == 0, really) will completely cover
2916 the old row, so the rows do not have to be
2917 initialized. After the first pass (and only
2918 for interlaced images), you will have to pass
2919 the current row, and the function will combine
2920 the old row and the new row.
2922 You can also call png_process_data_pause in this
2923 callback - see above.
2928 end_callback(png_structp png_ptr, png_infop info)
2930 /* This function is called after the whole image
2931 has been read, including any chunks after the
2932 image (up to and including the IEND). You
2933 will usually have the same info chunk as you
2934 had in the header, although some data may have
2935 been added to the comments and time fields.
2937 Most people won't do much here, perhaps setting
2938 a flag that marks the image as finished.
2946 Much of this is very similar to reading. However, everything of
2947 importance is repeated here, so you won't have to constantly look
2948 back up in the reading section to understand writing.
2952 You will want to do the I/O initialization before you get into libpng,
2953 so if it doesn't work, you don't have anything to undo. If you are not
2954 using the standard I/O functions, you will need to replace them with
2955 custom writing functions. See the discussion under Customizing libpng.
2957 FILE *fp = fopen(file_name, "wb");
2962 Next, png_struct and png_info need to be allocated and initialized.
2963 As these can be both relatively large, you may not want to store these
2964 on the stack, unless you have stack space to spare. Of course, you
2965 will want to check if they return NULL. If you are also reading,
2966 you won't want to name your read structure and your write structure
2967 both "png_ptr"; you can call them anything you like, such as
2968 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2970 png_structp png_ptr = png_create_write_struct
2971 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2972 user_error_fn, user_warning_fn);
2977 png_infop info_ptr = png_create_info_struct(png_ptr);
2980 png_destroy_write_struct(&png_ptr,
2985 If you want to use your own memory allocation routines,
2986 define PNG_USER_MEM_SUPPORTED and use
2987 png_create_write_struct_2() instead of png_create_write_struct():
2989 png_structp png_ptr = png_create_write_struct_2
2990 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2991 user_error_fn, user_warning_fn, (png_voidp)
2992 user_mem_ptr, user_malloc_fn, user_free_fn);
2994 After you have these structures, you will need to set up the
2995 error handling. When libpng encounters an error, it expects to
2996 longjmp() back to your routine. Therefore, you will need to call
2997 setjmp() and pass the png_jmpbuf(png_ptr). If you
2998 write the file from different routines, you will need to update
2999 the png_jmpbuf(png_ptr) every time you enter a new routine that will
3000 call a png_*() function. See your documentation of setjmp/longjmp
3001 for your compiler for more information on setjmp/longjmp. See
3002 the discussion on libpng error handling in the Customizing Libpng
3003 section below for more information on the libpng error handling.
3005 if (setjmp(png_jmpbuf(png_ptr)))
3007 png_destroy_write_struct(&png_ptr, &info_ptr);
3014 If you would rather avoid the complexity of setjmp/longjmp issues,
3015 you can compile libpng with PNG_NO_SETJMP, in which case
3016 errors will result in a call to PNG_ABORT() which defaults to abort().
3018 You can #define PNG_ABORT() to a function that does something
3019 more useful than abort(), as long as your function does not
3022 Now you need to set up the output code. The default for libpng is to
3023 use the C function fwrite(). If you use this, you will need to pass a
3024 valid FILE * in the function png_init_io(). Be sure that the file is
3025 opened in binary mode. Again, if you wish to handle writing data in
3026 another way, see the discussion on libpng I/O handling in the Customizing
3027 Libpng section below.
3029 png_init_io(png_ptr, fp);
3031 If you are embedding your PNG into a datastream such as MNG, and don't
3032 want libpng to write the 8-byte signature, or if you have already
3033 written the signature in your application, use
3035 png_set_sig_bytes(png_ptr, 8);
3037 to inform libpng that it should not write a signature.
3041 At this point, you can set up a callback function that will be
3042 called after each row has been written, which you can use to control
3043 a progress meter or the like. It's demonstrated in pngtest.c.
3044 You must supply a function
3046 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3049 /* put your code here */
3052 (You can give it another name that you like instead of "write_row_callback")
3054 To inform libpng about your function, use
3056 png_set_write_status_fn(png_ptr, write_row_callback);
3058 When this function is called the row has already been completely processed and
3059 it has also been written out. The 'row' and 'pass' refer to the next row to be
3061 non-interlaced case the row that was just handled is simply one less than the
3062 passed in row number, and pass will always be 0. For the interlaced case the
3063 same applies unless the row value is 0, in which case the row just handled was
3064 the last one from one of the preceding passes. Because interlacing may skip a
3065 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3066 need to know what the last pass is record (row,pass) from the callback and use
3067 the last recorded value each time.
3069 As with the user transform you can find the output row using the
3070 PNG_ROW_FROM_PASS_ROW macro.
3072 You now have the option of modifying how the compression library will
3073 run. The following functions are mainly for testing, but may be useful
3074 in some cases, like if you need to write PNG files extremely fast and
3075 are willing to give up some compression, or if you want to get the
3076 maximum possible compression at the expense of slower writing. If you
3077 have no special needs in this area, let the library do what it wants by
3078 not calling this function at all, as it has been tuned to deliver a good
3079 speed/compression ratio. The second parameter to png_set_filter() is
3080 the filter method, for which the only valid values are 0 (as of the
3081 July 1999 PNG specification, version 1.2) or 64 (if you are writing
3082 a PNG datastream that is to be embedded in a MNG datastream). The third
3083 parameter is a flag that indicates which filter type(s) are to be tested
3084 for each scanline. See the PNG specification for details on the specific
3088 /* turn on or off filtering, and/or choose
3089 specific filters. You can use either a single
3090 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3091 or more PNG_FILTER_NAME masks.
3093 png_set_filter(png_ptr, 0,
3094 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3095 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3096 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3097 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3098 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3101 If an application wants to start and stop using particular filters during
3102 compression, it should start out with all of the filters (to ensure that
3103 the previous row of pixels will be stored in case it's needed later),
3104 and then add and remove them after the start of compression.
3106 If you are writing a PNG datastream that is to be embedded in a MNG
3107 datastream, the second parameter can be either 0 or 64.
3109 The png_set_compression_*() functions interface to the zlib compression
3110 library, and should mostly be ignored unless you really know what you are
3111 doing. The only generally useful call is png_set_compression_level()
3112 which changes how much time zlib spends on trying to compress the image
3113 data. See the Compression Library (zlib.h and algorithm.txt, distributed
3114 with zlib) for details on the compression levels.
3118 /* Set the zlib compression level */
3119 png_set_compression_level(png_ptr,
3120 Z_BEST_COMPRESSION);
3122 /* Set other zlib parameters for compressing IDAT */
3123 png_set_compression_mem_level(png_ptr, 8);
3124 png_set_compression_strategy(png_ptr,
3125 Z_DEFAULT_STRATEGY);
3126 png_set_compression_window_bits(png_ptr, 15);
3127 png_set_compression_method(png_ptr, 8);
3128 png_set_compression_buffer_size(png_ptr, 8192)
3130 /* Set zlib parameters for text compression
3131 * If you don't call these, the parameters
3132 * fall back on those defined for IDAT chunks
3134 png_set_text_compression_mem_level(png_ptr, 8);
3135 png_set_text_compression_strategy(png_ptr,
3136 Z_DEFAULT_STRATEGY);
3137 png_set_text_compression_window_bits(png_ptr, 15);
3138 png_set_text_compression_method(png_ptr, 8);
3140 .SS Setting the contents of info for output
3142 You now need to fill in the png_info structure with all the data you
3143 wish to write before the actual image. Note that the only thing you
3144 are allowed to write after the image is the text chunks and the time
3145 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3146 the latest PNG specification for more information on that. If you
3147 wish to write them before the image, fill them in now, and flag that
3148 data as being valid. If you want to wait until after the data, don't
3149 fill them until png_write_end(). For all the fields in png_info and
3150 their data types, see png.h. For explanations of what the fields
3151 contain, see the PNG specification.
3153 Some of the more important parts of the png_info are:
3155 png_set_IHDR(png_ptr, info_ptr, width, height,
3156 bit_depth, color_type, interlace_type,
3157 compression_type, filter_method)
3159 width - holds the width of the image
3160 in pixels (up to 2^31).
3162 height - holds the height of the image
3163 in pixels (up to 2^31).
3165 bit_depth - holds the bit depth of one of the
3167 (valid values are 1, 2, 4, 8, 16
3168 and depend also on the
3169 color_type. See also significant
3172 color_type - describes which color/alpha
3173 channels are present.
3175 (bit depths 1, 2, 4, 8, 16)
3176 PNG_COLOR_TYPE_GRAY_ALPHA
3178 PNG_COLOR_TYPE_PALETTE
3179 (bit depths 1, 2, 4, 8)
3182 PNG_COLOR_TYPE_RGB_ALPHA
3185 PNG_COLOR_MASK_PALETTE
3186 PNG_COLOR_MASK_COLOR
3187 PNG_COLOR_MASK_ALPHA
3189 interlace_type - PNG_INTERLACE_NONE or
3192 compression_type - (must be
3193 PNG_COMPRESSION_TYPE_DEFAULT)
3195 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3196 or, if you are writing a PNG to
3197 be embedded in a MNG datastream,
3199 PNG_INTRAPIXEL_DIFFERENCING)
3201 If you call png_set_IHDR(), the call must appear before any of the
3202 other png_set_*() functions, because they might require access to some of
3203 the IHDR settings. The remaining png_set_*() functions can be called
3206 If you wish, you can reset the compression_type, interlace_type, or
3207 filter_method later by calling png_set_IHDR() again; if you do this, the
3208 width, height, bit_depth, and color_type must be the same in each call.
3210 png_set_PLTE(png_ptr, info_ptr, palette,
3213 palette - the palette for the file
3214 (array of png_color)
3215 num_palette - number of entries in the palette
3217 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3218 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3220 file_gamma - the gamma at which the image was
3221 created (PNG_INFO_gAMA)
3223 int_file_gamma - 100,000 times the gamma at which
3224 the image was created
3226 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3227 green_x, green_y, blue_x, blue_y)
3228 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3229 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3230 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3231 int_red_x, int_red_y, int_green_x, int_green_y,
3232 int_blue_x, int_blue_y)
3233 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3234 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3235 int_blue_X, int_blue_Y, int_blue_Z)
3237 {white,red,green,blue}_{x,y}
3238 A color space encoding specified using the chromaticities
3239 of the end points and the white point.
3241 {red,green,blue}_{X,Y,Z}
3242 A color space encoding specified using the encoding end
3243 points - the CIE tristimulus specification of the intended
3244 color of the red, green and blue channels in the PNG RGB
3245 data. The white point is simply the sum of the three end
3248 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3250 srgb_intent - the rendering intent
3251 (PNG_INFO_sRGB) The presence of
3252 the sRGB chunk means that the pixel
3253 data is in the sRGB color space.
3254 This chunk also implies specific
3255 values of gAMA and cHRM. Rendering
3256 intent is the CSS-1 property that
3257 has been defined by the International
3259 (http://www.color.org).
3261 PNG_sRGB_INTENT_SATURATION,
3262 PNG_sRGB_INTENT_PERCEPTUAL,
3263 PNG_sRGB_INTENT_ABSOLUTE, or
3264 PNG_sRGB_INTENT_RELATIVE.
3267 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3270 srgb_intent - the rendering intent
3271 (PNG_INFO_sRGB) The presence of the
3272 sRGB chunk means that the pixel
3273 data is in the sRGB color space.
3274 This function also causes gAMA and
3275 cHRM chunks with the specific values
3276 that are consistent with sRGB to be
3279 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3282 name - The profile name.
3284 compression_type - The compression type; always
3285 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3286 You may give NULL to this argument to
3289 profile - International Color Consortium color
3290 profile data. May contain NULs.
3292 proflen - length of profile data in bytes.
3294 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3296 sig_bit - the number of significant bits for
3297 (PNG_INFO_sBIT) each of the gray, red,
3298 green, and blue channels, whichever are
3299 appropriate for the given color type
3302 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3303 num_trans, trans_color);
3305 trans_alpha - array of alpha (transparency)
3306 entries for palette (PNG_INFO_tRNS)
3308 num_trans - number of transparent entries
3311 trans_color - graylevel or color sample values
3312 (in order red, green, blue) of the
3313 single transparent color for
3314 non-paletted images (PNG_INFO_tRNS)
3316 png_set_hIST(png_ptr, info_ptr, hist);
3318 hist - histogram of palette (array of
3319 png_uint_16) (PNG_INFO_hIST)
3321 png_set_tIME(png_ptr, info_ptr, mod_time);
3323 mod_time - time image was last modified
3326 png_set_bKGD(png_ptr, info_ptr, background);
3328 background - background color (of type
3329 png_color_16p) (PNG_VALID_bKGD)
3331 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3333 text_ptr - array of png_text holding image
3336 text_ptr[i].compression - type of compression used
3337 on "text" PNG_TEXT_COMPRESSION_NONE
3338 PNG_TEXT_COMPRESSION_zTXt
3339 PNG_ITXT_COMPRESSION_NONE
3340 PNG_ITXT_COMPRESSION_zTXt
3341 text_ptr[i].key - keyword for comment. Must contain
3343 text_ptr[i].text - text comments for current
3344 keyword. Can be NULL or empty.
3345 text_ptr[i].text_length - length of text string,
3346 after decompression, 0 for iTXt
3347 text_ptr[i].itxt_length - length of itxt string,
3348 after decompression, 0 for tEXt/zTXt
3349 text_ptr[i].lang - language of comment (NULL or
3351 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3352 or empty for unknown).
3354 Note that the itxt_length, lang, and lang_key
3355 members of the text_ptr structure only exist when the
3356 library is built with iTXt chunk support. Prior to
3357 libpng-1.4.0 the library was built by default without
3358 iTXt support. Also note that when iTXt is supported,
3359 they contain NULL pointers when the "compression"
3360 field contains PNG_TEXT_COMPRESSION_NONE or
3361 PNG_TEXT_COMPRESSION_zTXt.
3363 num_text - number of comments
3365 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3368 palette_ptr - array of png_sPLT_struct structures
3369 to be added to the list of palettes
3370 in the info structure.
3371 num_spalettes - number of palette structures to be
3374 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3377 offset_x - positive offset from the left
3380 offset_y - positive offset from the top
3383 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3385 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3388 res_x - pixels/unit physical resolution
3391 res_y - pixels/unit physical resolution
3394 unit_type - PNG_RESOLUTION_UNKNOWN,
3395 PNG_RESOLUTION_METER
3397 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3399 unit - physical scale units (an integer)
3401 width - width of a pixel in physical scale units
3403 height - height of a pixel in physical scale units
3404 (width and height are doubles)
3406 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3408 unit - physical scale units (an integer)
3410 width - width of a pixel in physical scale units
3411 expressed as a string
3413 height - height of a pixel in physical scale units
3414 (width and height are strings like "2.54")
3416 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3419 unknowns - array of png_unknown_chunk
3420 structures holding unknown chunks
3421 unknowns[i].name - name of unknown chunk
3422 unknowns[i].data - data of unknown chunk
3423 unknowns[i].size - size of unknown chunk's data
3424 unknowns[i].location - position to write chunk in file
3425 0: do not write chunk
3426 PNG_HAVE_IHDR: before PLTE
3427 PNG_HAVE_PLTE: before IDAT
3428 PNG_AFTER_IDAT: after IDAT
3430 The "location" member is set automatically according to
3431 what part of the output file has already been written.
3432 You can change its value after calling png_set_unknown_chunks()
3433 as demonstrated in pngtest.c. Within each of the "locations",
3434 the chunks are sequenced according to their position in the
3435 structure (that is, the value of "i", which is the order in which
3436 the chunk was either read from the input file or defined with
3437 png_set_unknown_chunks).
3439 A quick word about text and num_text. text is an array of png_text
3440 structures. num_text is the number of valid structures in the array.
3441 Each png_text structure holds a language code, a keyword, a text value,
3442 and a compression type.
3444 The compression types have the same valid numbers as the compression
3445 types of the image data. Currently, the only valid number is zero.
3446 However, you can store text either compressed or uncompressed, unlike
3447 images, which always have to be compressed. So if you don't want the
3448 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3449 Because tEXt and zTXt chunks don't have a language field, if you
3450 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3451 any language code or translated keyword will not be written out.
3453 Until text gets around a few hundred bytes, it is not worth compressing it.
3454 After the text has been written out to the file, the compression type
3455 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3456 so that it isn't written out again at the end (in case you are calling
3457 png_write_end() with the same struct).
3459 The keywords that are given in the PNG Specification are:
3461 Title Short (one line) title or
3464 Author Name of image's creator
3466 Description Description of image (possibly long)
3468 Copyright Copyright notice
3470 Creation Time Time of original image creation
3471 (usually RFC 1123 format, see below)
3473 Software Software used to create the image
3475 Disclaimer Legal disclaimer
3477 Warning Warning of nature of content
3479 Source Device used to create the image
3481 Comment Miscellaneous comment; conversion
3482 from other image format
3484 The keyword-text pairs work like this. Keywords should be short
3485 simple descriptions of what the comment is about. Some typical
3486 keywords are found in the PNG specification, as is some recommendations
3487 on keywords. You can repeat keywords in a file. You can even write
3488 some text before the image and some after. For example, you may want
3489 to put a description of the image before the image, but leave the
3490 disclaimer until after, so viewers working over modem connections
3491 don't have to wait for the disclaimer to go over the modem before
3492 they start seeing the image. Finally, keywords should be full
3493 words, not abbreviations. Keywords and text are in the ISO 8859-1
3494 (Latin-1) character set (a superset of regular ASCII) and can not
3495 contain NUL characters, and should not contain control or other
3496 unprintable characters. To make the comments widely readable, stick
3497 with basic ASCII, and avoid machine specific character set extensions
3498 like the IBM-PC character set. The keyword must be present, but
3499 you can leave off the text string on non-compressed pairs.
3500 Compressed pairs must have a text string, as only the text string
3501 is compressed anyway, so the compression would be meaningless.
3503 PNG supports modification time via the png_time structure. Two
3504 conversion routines are provided, png_convert_from_time_t() for
3505 time_t and png_convert_from_struct_tm() for struct tm. The
3506 time_t routine uses gmtime(). You don't have to use either of
3507 these, but if you wish to fill in the png_time structure directly,
3508 you should provide the time in universal time (GMT) if possible
3509 instead of your local time. Note that the year number is the full
3510 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3511 that months start with 1.
3513 If you want to store the time of the original image creation, you should
3514 use a plain tEXt chunk with the "Creation Time" keyword. This is
3515 necessary because the "creation time" of a PNG image is somewhat vague,
3516 depending on whether you mean the PNG file, the time the image was
3517 created in a non-PNG format, a still photo from which the image was
3518 scanned, or possibly the subject matter itself. In order to facilitate
3519 machine-readable dates, it is recommended that the "Creation Time"
3520 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3521 although this isn't a requirement. Unlike the tIME chunk, the
3522 "Creation Time" tEXt chunk is not expected to be automatically changed
3523 by the software. To facilitate the use of RFC 1123 dates, a function
3524 png_convert_to_rfc1123(png_ptr, png_timep) is provided to convert
3525 from PNG time to an RFC 1123 format string.
3527 .SS Writing unknown chunks
3529 You can use the png_set_unknown_chunks function to queue up chunks
3530 for writing. You give it a chunk name, raw data, and a size; that's
3531 all there is to it. The chunks will be written by the next following
3532 png_write_info_before_PLTE, png_write_info, or png_write_end function.
3533 Any chunks previously read into the info structure's unknown-chunk
3534 list will also be written out in a sequence that satisfies the PNG
3535 specification's ordering rules.
3537 .SS The high-level write interface
3539 At this point there are two ways to proceed; through the high-level
3540 write interface, or through a sequence of low-level write operations.
3541 You can use the high-level interface if your image data is present
3542 in the info structure. All defined output
3543 transformations are permitted, enabled by the following masks.
3545 PNG_TRANSFORM_IDENTITY No transformation
3546 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3547 PNG_TRANSFORM_PACKSWAP Change order of packed
3549 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3550 PNG_TRANSFORM_SHIFT Normalize pixels to the
3552 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3554 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3556 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3558 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
3559 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3561 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3563 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3566 If you have valid image data in the info structure (you can use
3567 png_set_rows() to put image data in the info structure), simply do this:
3569 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3571 where png_transforms is an integer containing the bitwise OR of some set of
3572 transformation flags. This call is equivalent to png_write_info(),
3573 followed the set of transformations indicated by the transform mask,
3574 then png_write_image(), and finally png_write_end().
3576 (The final parameter of this call is not yet used. Someday it might point
3577 to transformation parameters required by some future output transform.)
3579 You must use png_transforms and not call any png_set_transform() functions
3580 when you use png_write_png().
3582 .SS The low-level write interface
3584 If you are going the low-level route instead, you are now ready to
3585 write all the file information up to the actual image data. You do
3586 this with a call to png_write_info().
3588 png_write_info(png_ptr, info_ptr);
3590 Note that there is one transformation you may need to do before
3591 png_write_info(). In PNG files, the alpha channel in an image is the
3592 level of opacity. If your data is supplied as a level of transparency,
3593 you can invert the alpha channel before you write it, so that 0 is
3594 fully transparent and 255 (in 8-bit or paletted images) or 65535
3595 (in 16-bit images) is fully opaque, with
3597 png_set_invert_alpha(png_ptr);
3599 This must appear before png_write_info() instead of later with the
3600 other transformations because in the case of paletted images the tRNS
3601 chunk data has to be inverted before the tRNS chunk is written. If
3602 your image is not a paletted image, the tRNS data (which in such cases
3603 represents a single color to be rendered as transparent) won't need to
3604 be changed, and you can safely do this transformation after your
3605 png_write_info() call.
3607 If you need to write a private chunk that you want to appear before
3608 the PLTE chunk when PLTE is present, you can write the PNG info in
3609 two steps, and insert code to write your own chunk between them:
3611 png_write_info_before_PLTE(png_ptr, info_ptr);
3612 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3613 png_write_info(png_ptr, info_ptr);
3615 After you've written the file information, you can set up the library
3616 to handle any special transformations of the image data. The various
3617 ways to transform the data will be described in the order that they
3618 should occur. This is important, as some of these change the color
3619 type and/or bit depth of the data, and some others only work on
3620 certain color types and bit depths. Even though each transformation
3621 checks to see if it has data that it can do something with, you should
3622 make sure to only enable a transformation if it will be valid for the
3623 data. For example, don't swap red and blue on grayscale data.
3625 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3626 the library to strip input data that has 4 or 8 bytes per pixel down
3627 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3630 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3632 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3633 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3634 is stored XRGB or RGBX.
3636 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3637 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3638 If the data is supplied at 1 pixel per byte, use this code, which will
3639 correctly pack the pixels into a single byte:
3641 png_set_packing(png_ptr);
3643 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3644 data is of another bit depth, you can write an sBIT chunk into the
3645 file so that decoders can recover the original data if desired.
3647 /* Set the true bit depth of the image data */
3648 if (color_type & PNG_COLOR_MASK_COLOR)
3650 sig_bit.red = true_bit_depth;
3651 sig_bit.green = true_bit_depth;
3652 sig_bit.blue = true_bit_depth;
3657 sig_bit.gray = true_bit_depth;
3660 if (color_type & PNG_COLOR_MASK_ALPHA)
3662 sig_bit.alpha = true_bit_depth;
3665 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3667 If the data is stored in the row buffer in a bit depth other than
3668 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3669 this will scale the values to appear to be the correct bit depth as
3672 png_set_shift(png_ptr, &sig_bit);
3674 PNG files store 16-bit pixels in network byte order (big-endian,
3675 ie. most significant bits first). This code would be used if they are
3676 supplied the other way (little-endian, i.e. least significant bits
3677 first, the way PCs store them):
3680 png_set_swap(png_ptr);
3682 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3683 need to change the order the pixels are packed into bytes, you can use:
3686 png_set_packswap(png_ptr);
3688 PNG files store 3 color pixels in red, green, blue order. This code
3689 would be used if they are supplied as blue, green, red:
3691 png_set_bgr(png_ptr);
3693 PNG files describe monochrome as black being zero and white being
3694 one. This code would be used if the pixels are supplied with this reversed
3695 (black being one and white being zero):
3697 png_set_invert_mono(png_ptr);
3699 Finally, you can write your own transformation function if none of
3700 the existing ones meets your needs. This is done by setting a callback
3703 png_set_write_user_transform_fn(png_ptr,
3704 write_transform_fn);
3706 You must supply the function
3708 void write_transform_fn(png_structp png_ptr, png_row_infop
3709 row_info, png_bytep data)
3711 See pngtest.c for a working example. Your function will be called
3712 before any of the other transformations are processed. If supported
3713 libpng also supplies an information routine that may be called from
3716 png_get_current_row_number(png_ptr);
3717 png_get_current_pass_number(png_ptr);
3719 This returns the current row passed to the transform. With interlaced
3720 images the value returned is the row in the input sub-image image. Use
3721 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
3722 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
3724 The discussion of interlace handling above contains more information on how to
3727 You can also set up a pointer to a user structure for use by your
3730 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3732 The user_channels and user_depth parameters of this function are ignored
3733 when writing; you can set them to zero as shown.
3735 You can retrieve the pointer via the function png_get_user_transform_ptr().
3738 voidp write_user_transform_ptr =
3739 png_get_user_transform_ptr(png_ptr);
3741 It is possible to have libpng flush any pending output, either manually,
3742 or automatically after a certain number of lines have been written. To
3743 flush the output stream a single time call:
3745 png_write_flush(png_ptr);
3747 and to have libpng flush the output stream periodically after a certain
3748 number of scanlines have been written, call:
3750 png_set_flush(png_ptr, nrows);
3752 Note that the distance between rows is from the last time png_write_flush()
3753 was called, or the first row of the image if it has never been called.
3754 So if you write 50 lines, and then png_set_flush 25, it will flush the
3755 output on the next scanline, and every 25 lines thereafter, unless
3756 png_write_flush() is called before 25 more lines have been written.
3757 If nrows is too small (less than about 10 lines for a 640 pixel wide
3758 RGB image) the image compression may decrease noticeably (although this
3759 may be acceptable for real-time applications). Infrequent flushing will
3760 only degrade the compression performance by a few percent over images
3761 that do not use flushing.
3763 .SS Writing the image data
3765 That's it for the transformations. Now you can write the image data.
3766 The simplest way to do this is in one function call. If you have the
3767 whole image in memory, you can just call png_write_image() and libpng
3768 will write the image. You will need to pass in an array of pointers to
3769 each row. This function automatically handles interlacing, so you don't
3770 need to call png_set_interlace_handling() or call this function multiple
3771 times, or any of that other stuff necessary with png_write_rows().
3773 png_write_image(png_ptr, row_pointers);
3775 where row_pointers is:
3777 png_byte *row_pointers[height];
3779 You can point to void or char or whatever you use for pixels.
3781 If you don't want to write the whole image at once, you can
3782 use png_write_rows() instead. If the file is not interlaced,
3785 png_write_rows(png_ptr, row_pointers,
3788 row_pointers is the same as in the png_write_image() call.
3790 If you are just writing one row at a time, you can do this with
3791 a single row_pointer instead of an array of row_pointers:
3793 png_bytep row_pointer = row;
3795 png_write_row(png_ptr, row_pointer);
3797 When the file is interlaced, things can get a good deal more complicated.
3798 The only currently (as of the PNG Specification version 1.2, dated July
3799 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
3800 scheme, that breaks down an image into seven smaller images of varying
3801 size. libpng will build these images for you, or you can do them
3802 yourself. If you want to build them yourself, see the PNG specification
3803 for details of which pixels to write when.
3805 If you don't want libpng to handle the interlacing details, just
3806 use png_set_interlace_handling() and call png_write_rows() the
3807 correct number of times to write all the sub-images
3808 (png_set_interlace_handling() returns the number of sub-images.)
3810 If you want libpng to build the sub-images, call this before you start
3813 number_of_passes = png_set_interlace_handling(png_ptr);
3815 This will return the number of passes needed. Currently, this is seven,
3816 but may change if another interlace type is added.
3818 Then write the complete image number_of_passes times.
3820 png_write_rows(png_ptr, row_pointers, number_of_rows);
3822 Think carefully before you write an interlaced image. Typically code that
3823 reads such images reads all the image data into memory, uncompressed, before
3824 doing any processing. Only code that can display an image on the fly can
3825 take advantage of the interlacing and even then the image has to be exactly
3826 the correct size for the output device, because scaling an image requires
3827 adjacent pixels and these are not available until all the passes have been
3830 If you do write an interlaced image you will hardly ever need to handle
3831 the interlacing yourself. Call png_set_interlace_handling() and use the
3832 approach described above.
3834 The only time it is conceivable that you will really need to write an
3835 interlaced image pass-by-pass is when you have read one pass by pass and
3836 made some pixel-by-pixel transformation to it, as described in the read
3837 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
3838 to determine the size of each sub-image in turn and simply write the rows
3839 you obtained from the read code.
3841 .SS Finishing a sequential write
3843 After you are finished writing the image, you should finish writing
3844 the file. If you are interested in writing comments or time, you should
3845 pass an appropriately filled png_info pointer. If you are not interested,
3848 png_write_end(png_ptr, info_ptr);
3850 When you are done, you can free all memory used by libpng like this:
3852 png_destroy_write_struct(&png_ptr, &info_ptr);
3854 It is also possible to individually free the info_ptr members that
3855 point to libpng-allocated storage with the following function:
3857 png_free_data(png_ptr, info_ptr, mask, seq)
3859 mask - identifies data to be freed, a mask
3860 containing the bitwise OR of one or
3862 PNG_FREE_PLTE, PNG_FREE_TRNS,
3863 PNG_FREE_HIST, PNG_FREE_ICCP,
3864 PNG_FREE_PCAL, PNG_FREE_ROWS,
3865 PNG_FREE_SCAL, PNG_FREE_SPLT,
3866 PNG_FREE_TEXT, PNG_FREE_UNKN,
3867 or simply PNG_FREE_ALL
3869 seq - sequence number of item to be freed
3872 This function may be safely called when the relevant storage has
3873 already been freed, or has not yet been allocated, or was allocated
3874 by the user and not by libpng, and will in those cases do nothing.
3875 The "seq" parameter is ignored if only one item of the selected data
3876 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3877 are allowed for the data type identified in the mask, such as text or
3878 sPLT, only the n'th item in the structure is freed, where n is "seq".
3880 If you allocated data such as a palette that you passed in to libpng
3881 with png_set_*, you must not free it until just before the call to
3882 png_destroy_write_struct().
3884 The default behavior is only to free data that was allocated internally
3885 by libpng. This can be changed, so that libpng will not free the data,
3886 or so that it will free data that was allocated by the user with png_malloc()
3887 or png_calloc() and passed in via a png_set_*() function, with
3889 png_data_freer(png_ptr, info_ptr, freer, mask)
3892 PNG_DESTROY_WILL_FREE_DATA
3893 PNG_SET_WILL_FREE_DATA
3894 PNG_USER_WILL_FREE_DATA
3896 mask - which data elements are affected
3897 same choices as in png_free_data()
3899 For example, to transfer responsibility for some data from a read structure
3900 to a write structure, you could use
3902 png_data_freer(read_ptr, read_info_ptr,
3903 PNG_USER_WILL_FREE_DATA,
3904 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3906 png_data_freer(write_ptr, write_info_ptr,
3907 PNG_DESTROY_WILL_FREE_DATA,
3908 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3910 thereby briefly reassigning responsibility for freeing to the user but
3911 immediately afterwards reassigning it once more to the write_destroy
3912 function. Having done this, it would then be safe to destroy the read
3913 structure and continue to use the PLTE, tRNS, and hIST data in the write
3916 This function only affects data that has already been allocated.
3917 You can call this function before calling after the png_set_*() functions
3918 to control whether the user or png_destroy_*() is supposed to free the data.
3919 When the user assumes responsibility for libpng-allocated data, the
3920 application must use
3921 png_free() to free it, and when the user transfers responsibility to libpng
3922 for data that the user has allocated, the user must have used png_malloc()
3923 or png_calloc() to allocate it.
3925 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3926 separately, do not transfer responsibility for freeing text_ptr to libpng,
3927 because when libpng fills a png_text structure it combines these members with
3928 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3929 if you transfer responsibility for free'ing text_ptr from libpng to your
3930 application, your application must not separately free those members.
3931 For a more compact example of writing a PNG image, see the file example.c.
3933 .SH V. Modifying/Customizing libpng:
3935 There are two issues here. The first is changing how libpng does
3936 standard things like memory allocation, input/output, and error handling.
3937 The second deals with more complicated things like adding new chunks,
3938 adding new transformations, and generally changing how libpng works.
3939 Both of those are compile-time issues; that is, they are generally
3940 determined at the time the code is written, and there is rarely a need
3941 to provide the user with a means of changing them.
3943 Memory allocation, input/output, and error handling
3945 All of the memory allocation, input/output, and error handling in libpng
3946 goes through callbacks that are user-settable. The default routines are
3947 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3948 these functions, call the appropriate png_set_*_fn() function.
3950 Memory allocation is done through the functions png_malloc(), png_calloc(),
3951 and png_free(). The png_malloc() and png_free() functions currently just
3952 call the standard C functions and png_calloc() calls png_malloc() and then
3953 clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
3954 is not the same as the calloc(number, size) function provided by stdlib.h.
3955 There is limited support for certain systems with segmented memory
3956 architectures and the types of pointers declared by png.h match this; you
3957 will have to use appropriate pointers in your application. Since it is
3958 unlikely that the method of handling memory allocation on a platform
3959 will change between applications, these functions must be modified in
3960 the library at compile time. If you prefer to use a different method
3961 of allocating and freeing data, you can use png_create_read_struct_2() or
3962 png_create_write_struct_2() to register your own functions as described
3963 above. These functions also provide a void pointer that can be retrieved
3966 mem_ptr=png_get_mem_ptr(png_ptr);
3968 Your replacement memory functions must have prototypes as follows:
3970 png_voidp malloc_fn(png_structp png_ptr,
3971 png_alloc_size_t size);
3973 void free_fn(png_structp png_ptr, png_voidp ptr);
3975 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3976 function will normally call png_error() if it receives a NULL from the
3977 system memory allocator or from your replacement malloc_fn().
3979 Your free_fn() will never be called with a NULL ptr, since libpng's
3980 png_free() checks for NULL before calling free_fn().
3982 Input/Output in libpng is done through png_read() and png_write(),
3983 which currently just call fread() and fwrite(). The FILE * is stored in
3984 png_struct and is initialized via png_init_io(). If you wish to change
3985 the method of I/O, the library supplies callbacks that you can set
3986 through the function png_set_read_fn() and png_set_write_fn() at run
3987 time, instead of calling the png_init_io() function. These functions
3988 also provide a void pointer that can be retrieved via the function
3989 png_get_io_ptr(). For example:
3991 png_set_read_fn(png_structp read_ptr,
3992 voidp read_io_ptr, png_rw_ptr read_data_fn)
3994 png_set_write_fn(png_structp write_ptr,
3995 voidp write_io_ptr, png_rw_ptr write_data_fn,
3996 png_flush_ptr output_flush_fn);
3998 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3999 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4001 The replacement I/O functions must have prototypes as follows:
4003 void user_read_data(png_structp png_ptr,
4004 png_bytep data, png_size_t length);
4006 void user_write_data(png_structp png_ptr,
4007 png_bytep data, png_size_t length);
4009 void user_flush_data(png_structp png_ptr);
4011 The user_read_data() function is responsible for detecting and
4012 handling end-of-data errors.
4014 Supplying NULL for the read, write, or flush functions sets them back
4015 to using the default C stream functions, which expect the io_ptr to
4016 point to a standard *FILE structure. It is probably a mistake
4017 to use NULL for one of write_data_fn and output_flush_fn but not both
4018 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4019 It is an error to read from a write stream, and vice versa.
4021 Error handling in libpng is done through png_error() and png_warning().
4022 Errors handled through png_error() are fatal, meaning that png_error()
4023 should never return to its caller. Currently, this is handled via
4024 setjmp() and longjmp() (unless you have compiled libpng with
4025 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4026 but you could change this to do things like exit() if you should wish,
4027 as long as your function does not return.
4029 On non-fatal errors, png_warning() is called
4030 to print a warning message, and then control returns to the calling code.
4031 By default png_error() and png_warning() print a message on stderr via
4032 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4033 (because you don't want the messages) or PNG_NO_STDIO defined (because
4034 fprintf() isn't available). If you wish to change the behavior of the error
4035 functions, you will need to set up your own message callbacks. These
4036 functions are normally supplied at the time that the png_struct is created.
4037 It is also possible to redirect errors and warnings to your own replacement
4038 functions after png_create_*_struct() has been called by calling:
4040 png_set_error_fn(png_structp png_ptr,
4041 png_voidp error_ptr, png_error_ptr error_fn,
4042 png_error_ptr warning_fn);
4044 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4046 If NULL is supplied for either error_fn or warning_fn, then the libpng
4047 default function will be used, calling fprintf() and/or longjmp() if a
4048 problem is encountered. The replacement error functions should have
4049 parameters as follows:
4051 void user_error_fn(png_structp png_ptr,
4052 png_const_charp error_msg);
4054 void user_warning_fn(png_structp png_ptr,
4055 png_const_charp warning_msg);
4057 The motivation behind using setjmp() and longjmp() is the C++ throw and
4058 catch exception handling methods. This makes the code much easier to write,
4059 as there is no need to check every return code of every function call.
4060 However, there are some uncertainties about the status of local variables
4061 after a longjmp, so the user may want to be careful about doing anything
4062 after setjmp returns non-zero besides returning itself. Consult your
4063 compiler documentation for more details. For an alternative approach, you
4064 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4065 which is illustrated in pngvalid.c and in contrib/visupng.
4069 If you need to read or write custom chunks, you may need to get deeper
4070 into the libpng code. The library now has mechanisms for storing
4071 and writing chunks of unknown type; you can even declare callbacks
4072 for custom chunks. However, this may not be good enough if the
4073 library code itself needs to know about interactions between your
4074 chunk and existing `intrinsic' chunks.
4076 If you need to write a new intrinsic chunk, first read the PNG
4077 specification. Acquire a first level of understanding of how it works.
4078 Pay particular attention to the sections that describe chunk names,
4079 and look at how other chunks were designed, so you can do things
4080 similarly. Second, check out the sections of libpng that read and
4081 write chunks. Try to find a chunk that is similar to yours and use
4082 it as a template. More details can be found in the comments inside
4083 the code. It is best to handle private or unknown chunks in a generic method,
4084 via callback functions, instead of by modifying libpng functions. This
4085 is illustrated in pngtest.c, which uses a callback function to handle a
4086 private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4089 If you wish to write your own transformation for the data, look through
4090 the part of the code that does the transformations, and check out some of
4091 the simpler ones to get an idea of how they work. Try to find a similar
4092 transformation to the one you want to add and copy off of it. More details
4093 can be found in the comments inside the code itself.
4095 .SS Configuring for 16-bit platforms
4097 You will want to look into zconf.h to tell zlib (and thus libpng) that
4098 it cannot allocate more then 64K at a time. Even if you can, the memory
4099 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4101 .SS Configuring for DOS
4103 For DOS users who only have access to the lower 640K, you will
4104 have to limit zlib's memory usage via a png_set_compression_mem_level()
4105 call. See zlib.h or zconf.h in the zlib library for more information.
4107 .SS Configuring for Medium Model
4109 Libpng's support for medium model has been tested on most of the popular
4110 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4111 defined, and FAR gets defined to far in pngconf.h, and you should be
4112 all set. Everything in the library (except for zlib's structure) is
4113 expecting far data. You must use the typedefs with the p or pp on
4114 the end for pointers (or at least look at them and be careful). Make
4115 note that the rows of data are defined as png_bytepp, which is
4116 an "unsigned char far * far *".
4118 .SS Configuring for gui/windowing platforms:
4120 You will need to write new error and warning functions that use the GUI
4121 interface, as described previously, and set them to be the error and
4122 warning functions at the time that png_create_*_struct() is called,
4123 in order to have them available during the structure initialization.
4124 They can be changed later via png_set_error_fn(). On some compilers,
4125 you may also have to change the memory allocators (png_malloc, etc.).
4127 .SS Configuring for compiler xxx:
4129 All includes for libpng are in pngconf.h. If you need to add, change
4130 or delete an include, this is the place to do it.
4131 The includes that are not needed outside libpng are placed in pngpriv.h,
4132 which is only used by the routines inside libpng itself.
4133 The files in libpng proper only include pngpriv.h and png.h, which
4134 %14%in turn includes pngconf.h.
4135 in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4136 As of libpng-1.5.0, pngpriv.h also includes three other private header
4137 files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4138 that previously appeared in the public headers.
4140 .SS Configuring zlib:
4142 There are special functions to configure the compression. Perhaps the
4143 most useful one changes the compression level, which currently uses
4144 input compression values in the range 0 - 9. The library normally
4145 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4146 have shown that for a large majority of images, compression values in
4147 the range 3-6 compress nearly as well as higher levels, and do so much
4148 faster. For online applications it may be desirable to have maximum speed
4149 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4150 specify no compression (Z_NO_COMPRESSION = 0), but this would create
4151 files larger than just storing the raw bitmap. You can specify the
4152 compression level by calling:
4155 png_set_compression_level(png_ptr, level);
4157 Another useful one is to reduce the memory level used by the library.
4158 The memory level defaults to 8, but it can be lowered if you are
4159 short on memory (running DOS, for example, where you only have 640K).
4160 Note that the memory level does have an effect on compression; among
4161 other things, lower levels will result in sections of incompressible
4162 data being emitted in smaller stored blocks, with a correspondingly
4163 larger relative overhead of up to 15% in the worst case.
4166 png_set_compression_mem_level(png_ptr, level);
4168 The other functions are for configuring zlib. They are not recommended
4169 for normal use and may result in writing an invalid PNG file. See
4170 zlib.h for more information on what these mean.
4173 png_set_compression_strategy(png_ptr,
4176 png_set_compression_window_bits(png_ptr,
4179 png_set_compression_method(png_ptr, method);
4181 png_set_compression_buffer_size(png_ptr, size);
4183 As of libpng version 1.5.4, additional APIs became
4184 available to set these separately for non-IDAT
4185 compressed chunks such as zTXt, iTXt, and iCCP:
4188 #if PNG_LIBPNG_VER >= 10504
4189 png_set_text_compression_level(png_ptr, level);
4191 png_set_text_compression_mem_level(png_ptr, level);
4193 png_set_text_compression_strategy(png_ptr,
4196 png_set_text_compression_window_bits(png_ptr,
4199 png_set_text_compression_method(png_ptr, method);
4202 .SS Controlling row filtering
4204 If you want to control whether libpng uses filtering or not, which
4205 filters are used, and how it goes about picking row filters, you
4206 can call one of these functions. The selection and configuration
4207 of row filters can have a significant impact on the size and
4208 encoding speed and a somewhat lesser impact on the decoding speed
4209 of an image. Filtering is enabled by default for RGB and grayscale
4210 images (with and without alpha), but not for paletted images nor
4211 for any images with bit depths less than 8 bits/pixel.
4213 The 'method' parameter sets the main filtering method, which is
4214 currently only '0' in the PNG 1.2 specification. The 'filters'
4215 parameter sets which filter(s), if any, should be used for each
4216 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4217 to turn filtering on and off, respectively.
4219 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4220 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4221 ORed together with '|' to specify one or more filters to use.
4222 These filters are described in more detail in the PNG specification.
4223 If you intend to change the filter type during the course of writing
4224 the image, you should start with flags set for all of the filters
4225 you intend to use so that libpng can initialize its internal
4226 structures appropriately for all of the filter types. (Note that this
4227 means the first row must always be adaptively filtered, because libpng
4228 currently does not allocate the filter buffers until png_write_row()
4229 is called for the first time.)
4231 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4232 PNG_FILTER_UP | PNG_FILTER_AVG |
4233 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4235 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4237 The second parameter can also be
4238 PNG_INTRAPIXEL_DIFFERENCING if you are
4239 writing a PNG to be embedded in a MNG
4240 datastream. This parameter must be the
4241 same as the value of filter_method used
4244 It is also possible to influence how libpng chooses from among the
4245 available filters. This is done in one or both of two ways - by
4246 telling it how important it is to keep the same filter for successive
4247 rows, and by telling it the relative computational costs of the filters.
4249 double weights[3] = {1.5, 1.3, 1.1},
4250 costs[PNG_FILTER_VALUE_LAST] =
4251 {1.0, 1.3, 1.3, 1.5, 1.7};
4253 png_set_filter_heuristics(png_ptr,
4254 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4257 The weights are multiplying factors that indicate to libpng that the
4258 row filter should be the same for successive rows unless another row filter
4259 is that many times better than the previous filter. In the above example,
4260 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4261 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
4262 and still be chosen, while the NONE filter could have a sum 1.1 times
4263 higher than other filters and still be chosen. Unspecified weights are
4264 taken to be 1.0, and the specified weights should probably be declining
4265 like those above in order to emphasize recent filters over older filters.
4267 The filter costs specify for each filter type a relative decoding cost
4268 to be considered when selecting row filters. This means that filters
4269 with higher costs are less likely to be chosen over filters with lower
4270 costs, unless their "sum of absolute differences" is that much smaller.
4271 The costs do not necessarily reflect the exact computational speeds of
4272 the various filters, since this would unduly influence the final image
4275 Note that the numbers above were invented purely for this example and
4276 are given only to help explain the function usage. Little testing has
4277 been done to find optimum values for either the costs or the weights.
4279 .SS Removing unwanted object code
4281 There are a bunch of #define's in pngconf.h that control what parts of
4282 libpng are compiled. All the defines end in _SUPPORTED. If you are
4283 never going to use a capability, you can change the #define to #undef
4284 before recompiling libpng and save yourself code and data space, or
4285 you can turn off individual capabilities with defines that begin with
4288 In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4290 You can also turn all of the transforms and ancillary chunk capabilities
4291 off en masse with compiler directives that define
4292 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4294 along with directives to turn on any of the capabilities that you do
4295 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4296 transformations but still leave the library fully capable of reading
4297 and writing PNG files with all known public chunks. Use of the
4298 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4299 that is incapable of reading or writing ancillary chunks. If you are
4300 not using the progressive reading capability, you can turn that off
4301 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4302 capability, which you'll still have).
4304 All the reading and writing specific code are in separate files, so the
4305 linker should only grab the files it needs. However, if you want to
4306 make sure, or if you are building a stand alone library, all the
4307 reading files start with "pngr" and all the writing files start with "pngw".
4308 The files that don't match either (like png.c, pngtrans.c, etc.)
4309 are used for both reading and writing, and always need to be included.
4310 The progressive reader is in pngpread.c
4312 If you are creating or distributing a dynamically linked library (a .so
4313 or DLL file), you should not remove or disable any parts of the library,
4314 as this will cause applications linked with different versions of the
4315 library to fail if they call functions not available in your library.
4316 The size of the library itself should not be an issue, because only
4317 those sections that are actually used will be loaded into memory.
4319 .SS Requesting debug printout
4321 The macro definition PNG_DEBUG can be used to request debugging
4322 printout. Set it to an integer value in the range 0 to 3. Higher
4323 numbers result in increasing amounts of debugging information. The
4324 information is printed to the "stderr" file, unless another file
4325 name is specified in the PNG_DEBUG_FILE macro definition.
4327 When PNG_DEBUG > 0, the following functions (macros) become available:
4329 png_debug(level, message)
4330 png_debug1(level, message, p1)
4331 png_debug2(level, message, p1, p2)
4333 in which "level" is compared to PNG_DEBUG to decide whether to print
4334 the message, "message" is the formatted string to be printed,
4335 and p1 and p2 are parameters that are to be embedded in the string
4336 according to printf-style formatting directives. For example,
4338 png_debug1(2, "foo=%d\n", foo);
4343 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4345 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4346 can still use PNG_DEBUG to control your own debugging:
4352 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4353 having level = 0 will be printed. There aren't any such statements in
4354 this version of libpng, but if you insert some they will be printed.
4358 The MNG specification (available at http://www.libpng.org/pub/mng) allows
4359 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4360 Libpng can support some of these extensions. To enable them, use the
4361 png_permit_mng_features() function:
4363 feature_set = png_permit_mng_features(png_ptr, mask)
4365 mask is a png_uint_32 containing the bitwise OR of the
4366 features you want to enable. These include
4367 PNG_FLAG_MNG_EMPTY_PLTE
4368 PNG_FLAG_MNG_FILTER_64
4369 PNG_ALL_MNG_FEATURES
4371 feature_set is a png_uint_32 that is the bitwise AND of
4372 your mask with the set of MNG features that is
4373 supported by the version of libpng that you are using.
4375 It is an error to use this function when reading or writing a standalone
4376 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4377 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4378 and the MHDR and MEND chunks. Libpng does not provide support for these
4379 or any other MNG chunks; your application must provide its own support for
4380 them. You may wish to consider using libmng (available at
4381 http://www.libmng.com) instead.
4383 .SH VII. Changes to Libpng from version 0.88
4385 It should be noted that versions of libpng later than 0.96 are not
4386 distributed by the original libpng author, Guy Schalnat, nor by
4387 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4388 distributed versions 0.89 through 0.96, but rather by another member
4389 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4390 still alive and well, but they have moved on to other things.
4392 The old libpng functions png_read_init(), png_write_init(),
4393 png_info_init(), png_read_destroy(), and png_write_destroy() have been
4394 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4395 functions will be removed from libpng version 1.4.0.
4397 The preferred method of creating and initializing the libpng structures is
4398 via the png_create_read_struct(), png_create_write_struct(), and
4399 png_create_info_struct() because they isolate the size of the structures
4400 from the application, allow version error checking, and also allow the
4401 use of custom error handling routines during the initialization, which
4402 the old functions do not. The functions png_read_destroy() and
4403 png_write_destroy() do not actually free the memory that libpng
4404 allocated for these structs, but just reset the data structures, so they
4405 can be used instead of png_destroy_read_struct() and
4406 png_destroy_write_struct() if you feel there is too much system overhead
4407 allocating and freeing the png_struct for each image read.
4409 Setting the error callbacks via png_set_message_fn() before
4410 png_read_init() as was suggested in libpng-0.88 is no longer supported
4411 because this caused applications that do not use custom error functions
4412 to fail if the png_ptr was not initialized to zero. It is still possible
4413 to set the error callbacks AFTER png_read_init(), or to change them with
4414 png_set_error_fn(), which is essentially the same function, but with a new
4415 name to force compilation errors with applications that try to use the old
4418 Starting with version 1.0.7, you can find out which version of the library
4419 you are using at run-time:
4421 png_uint_32 libpng_vn = png_access_version_number();
4423 The number libpng_vn is constructed from the major version, minor
4424 version with leading zero, and release number with leading zero,
4425 (e.g., libpng_vn for version 1.0.7 is 10007).
4427 Note that this function does not take a png_ptr, so you can call it
4428 before you've created one.
4430 You can also check which version of png.h you used when compiling your
4433 png_uint_32 application_vn = PNG_LIBPNG_VER;
4435 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
4437 Support for user memory management was enabled by default. To
4438 accomplish this, the functions png_create_read_struct_2(),
4439 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4440 png_malloc_default(), and png_free_default() were added.
4442 Support for the iTXt chunk has been enabled by default as of
4445 Support for certain MNG features was enabled.
4447 Support for numbered error messages was added. However, we never got
4448 around to actually numbering the error messages. The function
4449 png_set_strip_error_numbers() was added (Note: the prototype for this
4450 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4451 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4453 The png_malloc_warn() function was added at libpng-1.2.3. This issues
4454 a png_warning and returns NULL instead of aborting when it fails to
4455 acquire the requested memory allocation.
4457 Support for setting user limits on image width and height was enabled
4458 by default. The functions png_set_user_limits(), png_get_user_width_max(),
4459 and png_get_user_height_max() were added at libpng-1.2.6.
4461 The png_set_add_alpha() function was added at libpng-1.2.7.
4463 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4464 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4465 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4468 A number of macro definitions in support of runtime selection of
4469 assembler code features (especially Intel MMX code support) were
4470 added at libpng-1.2.0:
4472 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4473 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4474 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4475 PNG_ASM_FLAG_MMX_READ_INTERLACE
4476 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4477 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4478 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4479 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4480 PNG_ASM_FLAGS_INITIALIZED
4486 We added the following functions in support of runtime
4487 selection of assembler code features:
4489 png_get_mmx_flagmask()
4490 png_set_mmx_thresholds()
4492 png_get_mmx_bitdepth_threshold()
4493 png_get_mmx_rowbytes_threshold()
4496 We replaced all of these functions with simple stubs in libpng-1.2.20,
4497 when the Intel assembler code was removed due to a licensing issue.
4499 These macros are deprecated:
4501 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4502 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4503 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4504 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4505 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4506 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4508 They have been replaced, respectively, by:
4510 PNG_NO_READ_TRANSFORMS
4511 PNG_NO_PROGRESSIVE_READ
4512 PNG_NO_SEQUENTIAL_READ
4513 PNG_NO_WRITE_TRANSFORMS
4514 PNG_NO_READ_ANCILLARY_CHUNKS
4515 PNG_NO_WRITE_ANCILLARY_CHUNKS
4517 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4518 deprecated since libpng-1.0.16 and libpng-1.2.6.
4521 png_check_sig(sig, num)
4523 !png_sig_cmp(sig, 0, num)
4524 It has been deprecated since libpng-0.90.
4527 png_set_gray_1_2_4_to_8()
4528 which also expands tRNS to alpha was replaced with
4529 png_set_expand_gray_1_2_4_to_8()
4530 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
4532 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
4534 Private libpng prototypes and macro definitions were moved from
4535 png.h and pngconf.h into a new pngpriv.h header file.
4537 Functions png_set_benign_errors(), png_benign_error(), and
4538 png_chunk_benign_error() were added.
4540 Support for setting the maximum amount of memory that the application
4541 will allocate for reading chunks was added, as a security measure.
4542 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
4543 were added to the library.
4545 We implemented support for I/O states by adding png_ptr member io_state
4546 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
4548 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
4551 Checking for and reporting of errors in the IHDR chunk is more thorough.
4553 Support for global arrays was removed, to improve thread safety.
4555 Some obsolete/deprecated macros and functions have been removed.
4557 Typecasted NULL definitions such as
4558 #define png_voidp_NULL (png_voidp)NULL
4559 were eliminated. If you used these in your application, just use
4562 The png_struct and info_struct members "trans" and "trans_values" were
4563 changed to "trans_alpha" and "trans_color", respectively.
4565 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
4568 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
4570 The PNG_LEGACY_SUPPORTED macro was eliminated.
4572 Many WIN32_WCE #ifdefs were removed.
4574 The functions png_read_init(info_ptr), png_write_init(info_ptr),
4575 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
4576 have been removed. They have been deprecated since libpng-0.95.
4578 The png_permit_empty_plte() was removed. It has been deprecated
4579 since libpng-1.0.9. Use png_permit_mng_features() instead.
4581 We removed the obsolete stub functions png_get_mmx_flagmask(),
4582 png_set_mmx_thresholds(), png_get_asm_flags(),
4583 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
4584 png_set_asm_flags(), and png_mmx_supported()
4586 We removed the obsolete png_check_sig(), png_memcpy_check(), and
4587 png_memset_check() functions. Instead use !png_sig_cmp(), png_memcpy(),
4588 and png_memset(), respectively.
4590 The function png_set_gray_1_2_4_to_8() was removed. It has been
4591 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
4592 png_set_expand_gray_1_2_4_to_8() because the former function also
4593 expanded any tRNS chunk to an alpha channel.
4595 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
4596 were added and are used by default instead of the corresponding
4597 functions. Unfortunately,
4598 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4599 function) incorrectly returned a value of type png_uint_32.
4601 We changed the prototype for png_malloc() from
4602 png_malloc(png_structp png_ptr, png_uint_32 size)
4604 png_malloc(png_structp png_ptr, png_alloc_size_t size)
4606 This also applies to the prototype for the user replacement malloc_fn().
4608 The png_calloc() function was added and is used in place of
4609 of "png_malloc(); memset();" except in the case in png_read_png()
4610 where the array consists of pointers; in this case a "for" loop is used
4611 after the png_malloc() to set the pointers to NULL, to give robust.
4612 behavior in case the application runs out of memory part-way through
4615 We changed the prototypes of png_get_compression_buffer_size() and
4616 png_set_compression_buffer_size() to work with png_size_t instead of
4619 Support for numbered error messages was removed by default, since we
4620 never got around to actually numbering the error messages. The function
4621 png_set_strip_error_numbers() was removed from the library by default.
4623 The png_zalloc() and png_zfree() functions are no longer exported.
4624 The png_zalloc() function no longer zeroes out the memory that it
4625 allocates. Applications that called png_zalloc(png_ptr, number, size)
4626 can call png_calloc(png_ptr, number*size) instead, and can call
4627 png_free() instead of png_zfree().
4629 Support for dithering was disabled by default in libpng-1.4.0, because
4630 it has not been well tested and doesn't actually "dither".
4632 removed, however, and could be enabled by building libpng with
4633 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
4634 was reenabled, but the function was renamed png_set_quantize() to
4635 reflect more accurately what it actually does. At the same time,
4636 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
4637 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
4638 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
4640 We removed the trailing '.' from the warning and error messages.
4642 .SH X. Changes to Libpng from version 1.4.x to 1.5.x
4644 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4645 function) incorrectly returned a value of type png_uint_32.
4647 Checking for invalid palette index on read or write was added at libpng
4648 1.5.10. When an invalid index is found, libpng issues a benign error.
4649 This is enabled by default but can be disabled in each png_ptr with
4651 png_set_check_for_invalid_index(png_ptr, allowed);
4657 A. Changes that affect users of libpng
4659 There are no substantial API changes between the non-deprecated parts of
4660 the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
4661 members of the main libpng control structures, png_struct and png_info,
4662 deprecated in earlier versions of libpng, has been completely removed from
4665 We no longer include zlib.h in png.h. Applications that need access
4666 to information in zlib.h will need to add the '#include "zlib.h"'
4667 directive. It does not matter whether it is placed prior to or after
4668 the '"#include png.h"' directive.
4670 The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
4673 We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
4674 macros into a private header file (pngpriv.h) that is not accessible to
4677 In png_get_iCCP, the type of "profile" was changed from png_charpp
4678 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
4680 There are changes of form in png.h, including new and changed macros to
4681 declare parts of the API. Some API functions with arguments that are
4682 pointers to data not modified within the function have been corrected to
4683 declare these arguments with PNG_CONST.
4685 Much of the internal use of C macros to control the library build has also
4686 changed and some of this is visible in the exported header files, in
4687 particular the use of macros to control data and API elements visible
4688 during application compilation may require significant revision to
4689 application code. (It is extremely rare for an application to do this.)
4691 Any program that compiled against libpng 1.4 and did not use deprecated
4692 features or access internal library structures should compile and work
4693 against libpng 1.5, except for the change in the prototype for
4694 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
4696 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
4697 interlaced images. The macros return the number of rows and columns in
4698 each pass and information that can be used to de-interlace and (if
4699 absolutely necessary) interlace an image.
4701 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
4702 the application-provided png_longjmp_ptr on the internal, but application
4703 initialized, longjmp buffer. It is provided as a convenience to avoid
4704 the need to use the png_jmpbuf macro, which had the unnecessary side
4705 effect of resetting the internal png_longjmp_ptr value.
4707 libpng 1.5.0 includes a complete fixed point API. By default this is
4708 present along with the corresponding floating point API. In general the
4709 fixed point API is faster and smaller than the floating point one because
4710 the PNG file format used fixed point, not floating point. This applies
4711 even if the library uses floating point in internal calculations. A new
4712 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
4713 uses floating point arithmetic (the default) or fixed point arithmetic
4714 internally for performance critical calculations such as gamma correction.
4715 In some cases, the gamma calculations may produce slightly different
4716 results. This has changed the results in png_rgb_to_gray and in alpha
4717 composition (png_set_background for example). This applies even if the
4718 original image was already linear (gamma == 1.0) and, therefore, it is
4719 not necessary to linearize the image. This is because libpng has *not*
4720 been changed to optimize that case correctly, yet.
4722 Fixed point support for the sCAL chunk comes with an important caveat;
4723 the sCAL specification uses a decimal encoding of floating point values
4724 and the accuracy of PNG fixed point values is insufficient for
4725 representation of these values. Consequently a "string" API
4726 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
4727 arbitrary sCAL chunks in the absence of either the floating point API or
4728 internal floating point calculations.
4730 Applications no longer need to include the optional distribution header
4731 file pngusr.h or define the corresponding macros during application
4732 build in order to see the correct variant of the libpng API. From 1.5.0
4733 application code can check for the corresponding _SUPPORTED macro:
4735 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
4736 /* code that uses the inch conversion APIs. */
4739 This macro will only be defined if the inch conversion functions have been
4740 compiled into libpng. The full set of macros, and whether or not support
4741 has been compiled in, are available in the header file pnglibconf.h.
4742 This header file is specific to the libpng build. Notice that prior to
4743 1.5.0 the _SUPPORTED macros would always have the default definition unless
4744 reset by pngusr.h or by explicit settings on the compiler command line.
4745 These settings may produce compiler warnings or errors in 1.5.0 because
4746 of macro redefinition.
4748 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4749 function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
4750 is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
4753 Applications can now choose whether to use these macros or to call the
4754 corresponding function by defining PNG_USE_READ_MACROS or
4755 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
4756 only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
4757 will lead to a link failure.
4759 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
4760 when compressing the IDAT data and textual data such as zTXt and iCCP.
4761 In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
4762 We added five png_set_text_*() functions for setting the parameters to
4763 use with textual data.
4765 Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
4766 option was off by default, and slightly inaccurate scaling occurred.
4767 This option can no longer be turned off, and the choice of accurate
4768 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
4769 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
4772 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
4773 used to reduce the width and height limits from the value of
4774 PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
4775 that it could be used to override them. Now this function will reduce or
4776 increase the limits.
4778 Starting in libpng-1.5.10, the user limits can be set en masse with the
4779 configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
4780 a set of "safe" limits is applied in pngpriv.h. These can be overridden by
4781 application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
4782 and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
4783 in libpng-1.5.10 the default width and height limits were increased
4784 from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
4787 png_user_width_max 0x7fffffff 1,000,000
4788 png_user_height_max 0x7fffffff 1,000,000
4789 png_user_chunk_cache_max 0 (unlimited) 128
4790 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
4792 B. Changes to the build and configuration of libpng
4794 Details of internal changes to the library code can be found in the CHANGES
4795 file and in the GIT repository logs. These will be of no concern to the vast
4796 majority of library users or builders; however, the few who configure libpng
4797 to a non-default feature set may need to change how this is done.
4799 There should be no need for library builders to alter build scripts if
4800 these use the distributed build support - configure or the makefiles -
4801 however, users of the makefiles may care to update their build scripts
4802 to build pnglibconf.h where the corresponding makefile does not do so.
4804 Building libpng with a non-default configuration has changed completely.
4805 The old method using pngusr.h should still work correctly even though the
4806 way pngusr.h is used in the build has been changed; however, library
4807 builders will probably want to examine the changes to take advantage of
4808 new capabilities and to simplify their build system.
4810 B.1 Specific changes to library configuration capabilities
4812 The library now supports a complete fixed point implementation and can
4813 thus be used on systems that have no floating point support or very
4814 limited or slow support. Previously gamma correction, an essential part
4815 of complete PNG support, required reasonably fast floating point.
4817 As part of this the choice of internal implementation has been made
4818 independent of the choice of fixed versus floating point APIs and all the
4819 missing fixed point APIs have been implemented.
4821 The exact mechanism used to control attributes of API functions has
4822 changed. A single set of operating system independent macro definitions
4823 is used and operating system specific directives are defined in
4826 As part of this the mechanism used to choose procedure call standards on
4827 those systems that allow a choice has been changed. At present this only
4828 affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
4829 running on Intel processors. As before, PNGAPI is defined where required
4830 to control the exported API functions; however, two new macros, PNGCBAPI
4831 and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
4832 (PNGCAPI) for functions that must match a C library prototype (currently
4833 only png_longjmp_ptr, which must match the C longjmp function.) The new
4834 approach is documented in pngconf.h
4836 Despite these changes, libpng 1.5.0 only supports the native C function
4837 calling standard on those platforms tested so far (__cdecl on Microsoft
4838 Windows). This is because the support requirements for alternative
4839 calling conventions seem to no longer exist. Developers who find it
4840 necessary to set PNG_API_RULE to 1 should advise the mailing list
4841 (png-mng-implement) of this and library builders who use Openwatcom and
4842 therefore set PNG_API_RULE to 2 should also contact the mailing list.
4844 A new test program, pngvalid, is provided in addition to pngtest.
4845 pngvalid validates the arithmetic accuracy of the gamma correction
4846 calculations and includes a number of validations of the file format.
4847 A subset of the full range of tests is run when "make check" is done
4848 (in the 'configure' build.) pngvalid also allows total allocated memory
4849 usage to be evaluated and performs additional memory overwrite validation.
4851 Many changes to individual feature macros have been made. The following
4852 are the changes most likely to be noticed by library builders who
4855 1) All feature macros now have consistent naming:
4857 #define PNG_NO_feature turns the feature off
4858 #define PNG_feature_SUPPORTED turns the feature on
4860 pnglibconf.h contains one line for each feature macro which is either:
4862 #define PNG_feature_SUPPORTED
4864 if the feature is supported or:
4866 /*#undef PNG_feature_SUPPORTED*/
4868 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
4869 It does not, and libpng applications should not, check for the 'NO' macro
4870 which will not normally be defined even if the feature is not supported.
4871 The 'NO' macros are only used internally for setting or not setting the
4872 corresponding 'SUPPORTED' macros.
4874 Compatibility with the old names is provided as follows:
4876 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
4878 And the following definitions disable the corresponding feature:
4880 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
4881 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
4882 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
4883 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
4884 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
4885 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
4887 Library builders should remove use of the above, inconsistent, names.
4889 2) Warning and error message formatting was previously conditional on
4890 the STDIO feature. The library has been changed to use the
4891 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
4892 the library no longer uses the printf(3) functions, even though the
4893 default read/write implementations use (FILE) style stdio.h functions.
4895 3) Three feature macros now control the fixed/floating point decisions:
4897 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
4899 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
4900 practice these are normally required internally anyway (because the PNG
4901 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
4902 merely stops the function from being exported.
4904 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
4905 point implementation or the fixed point one. Typically the fixed point
4906 implementation is larger and slower than the floating point implementation
4907 on a system that supports floating point; however, it may be faster on a
4908 system which lacks floating point hardware and therefore uses a software
4911 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
4912 functions to read and write ints to be disabled independently of
4913 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
4914 even though the default is to use the macros - this allows applications
4915 to choose at app buildtime whether or not to use macros (previously
4916 impossible because the functions weren't in the default build.)
4918 B.2 Changes to the configuration mechanism
4920 Prior to libpng-1.5.0 library builders who needed to configure libpng
4921 had either to modify the exported pngconf.h header file to add system
4922 specific configuration or had to write feature selection macros into
4923 pngusr.h and cause this to be included into pngconf.h by defining
4924 PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
4925 application built without PNG_USER_CONFIG defined would see the
4926 unmodified, default, libpng API and thus would probably fail to link.
4928 These mechanisms still work in the configure build and in any makefile
4929 build that builds pnglibconf.h, although the feature selection macros
4930 have changed somewhat as described above. In 1.5.0, however, pngusr.h is
4931 processed only once, when the exported header file pnglibconf.h is built.
4932 pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
4933 build of pnglibconf.h and it is never included in an application build.
4935 The rarely used alternative of adding a list of feature macros to the
4936 CFLAGS setting in the build also still works; however, the macros will be
4937 copied to pnglibconf.h and this may produce macro redefinition warnings
4938 when the individual C files are compiled.
4940 All configuration now only works if pnglibconf.h is built from
4941 scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
4942 (the original author of awk) maintains C source code of that awk and this
4943 and all known later implementations (often called by subtly different
4944 names - nawk and gawk for example) are adequate to build pnglibconf.h.
4945 The Sun Microsystems (now Oracle) program 'awk' is an earlier version
4946 and does not work; this may also apply to other systems that have a
4947 functioning awk called 'nawk'.
4949 Configuration options are now documented in scripts/pnglibconf.dfa. This
4950 file also includes dependency information that ensures a configuration is
4951 consistent; that is, if a feature is switched off dependent features are
4952 also removed. As a recommended alternative to using feature macros in
4953 pngusr.h a system builder may also define equivalent options in pngusr.dfa
4954 (or, indeed, any file) and add that to the configuration by setting
4955 DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
4956 how to do this, and a case where pngusr.h is still required.
4958 .SH XI. Detecting libpng
4960 The png_get_io_ptr() function has been present since libpng-0.88, has never
4961 changed, and is unaffected by conditional compilation macros. It is the
4962 best choice for use in configure scripts for detecting the presence of any
4963 libpng version since 0.88. In an autoconf "configure.in" you could use
4965 AC_CHECK_LIB(png, png_get_io_ptr, ...
4967 .SH XII. Source code repository
4969 Since about February 2009, version 1.2.34, libpng has been under "git" source
4970 control. The git repository was built from old libpng-x.y.z.tar.gz files
4971 going back to version 0.70. You can access the git repository (read only)
4974 git://libpng.git.sourceforge.net/gitroot/libpng
4976 or you can browse it via "gitweb" at
4978 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
4980 Patches can be sent to glennrp at users.sourceforge.net or to
4981 png-mng-implement at lists.sourceforge.net or you can upload them to
4982 the libpng bug tracker at
4984 http://libpng.sourceforge.net
4986 We also accept patches built from the tar or zip distributions, and
4987 simple verbal discriptions of bug fixes, reported either to the
4988 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
4989 mailing list, or directly to glennrp.
4991 .SH XIII. Coding style
4993 Our coding style is similar to the "Allman" style, with curly
4994 braces on separate lines:
5001 else if (another condition)
5006 The braces can be omitted from simple one-line actions:
5011 We use 3-space indentation, except for continued statements which
5012 are usually indented the same as the first line of the statement
5013 plus four more spaces.
5015 For macro definitions we use 2-space indentation, always leaving the "#"
5016 in the first column.
5018 #ifndef PNG_NO_FEATURE
5019 # ifndef PNG_FEATURE_SUPPORTED
5020 # define PNG_FEATURE_SUPPORTED
5024 Comments appear with the leading "/*" at the same indentation as
5025 the statement that follows the comment:
5027 /* Single-line comment */
5030 /* This is a multiple-line
5035 Very short comments can be placed after the end of the statement
5036 to which they pertain:
5038 statement; /* comment */
5040 We don't use C++ style ("//") comments. We have, however,
5041 used them in the past in some now-abandoned MMX assembler
5044 Functions and their curly braces are not indented, and
5045 exported functions are marked with PNGAPI:
5047 /* This is a public function that is visible to
5048 * application programmers. It does thus-and-so.
5051 png_exported_function(png_ptr, png_info, foo)
5056 The prototypes for all exported functions appear in png.h,
5057 above the comment that says
5059 /* Maintainer: Put new public prototypes here ... */
5061 We mark all non-exported functions with "/* PRIVATE */"":
5064 png_non_exported_function(png_ptr, png_info, foo)
5069 The prototypes for non-exported functions (except for those in
5072 above the comment that says
5074 /* Maintainer: Put new private prototypes here ^ */
5076 To avoid polluting the global namespace, the names of all exported
5077 functions and variables begin with "png_", and all publicly visible C
5078 preprocessor macros begin with "PNG". We request that applications that
5079 use libpng *not* begin any of their own symbols with either of these strings.
5081 We put a space after each comma and after each semicolon
5082 in "for" statements, and we put spaces before and after each
5083 C binary operator and after "for" or "while", and before
5084 "?". We don't put a space between a typecast and the expression
5085 being cast, nor do we put one between a function name and the
5086 left parenthesis that follows it:
5088 for (i = 2; i > 0; --i)
5089 y[i] = a(x) + (int)b;
5091 We prefer #ifdef and #ifndef to #if defined() and #if !defined()
5092 when there is only one macro being tested.
5094 We prefer to express integers that are used as bit masks in hex format,
5095 with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5097 We do not use the TAB character for indentation in the C sources.
5099 Lines do not exceed 80 characters.
5101 Other rules can be inferred by inspecting the libpng source.
5103 .SH XIV. Y2K Compliance in libpng
5107 Since the PNG Development group is an ad-hoc body, we can't make
5108 an official declaration.
5110 This is your unofficial assurance that libpng from version 0.71 and
5111 upward through 1.5.14 are Y2K compliant. It is my belief that earlier
5112 versions were also Y2K compliant.
5114 Libpng only has two year fields. One is a 2-byte unsigned integer that
5115 will hold years up to 65535. The other holds the date in text
5116 format, and will hold years up to 9999.
5119 "png_uint_16 year" in png_time_struct.
5122 "char time_buffer[29]" in png_struct. This will no
5123 longer be used in libpng-1.6.x and will be removed from libpng-1.7.0.
5125 There are seven time-related functions:
5127 png_convert_to_rfc_1123() in png.c
5128 (formerly png_convert_to_rfc_1152() in error)
5129 png_convert_from_struct_tm() in pngwrite.c, called
5131 png_convert_from_time_t() in pngwrite.c
5132 png_get_tIME() in pngget.c
5133 png_handle_tIME() in pngrutil.c, called in pngread.c
5134 png_set_tIME() in pngset.c
5135 png_write_tIME() in pngwutil.c, called in pngwrite.c
5137 All appear to handle dates properly in a Y2K environment. The
5138 png_convert_from_time_t() function calls gmtime() to convert from system
5139 clock time, which returns (year - 1900), which we properly convert to
5140 the full 4-digit year. There is a possibility that applications using
5141 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5142 function, or that they are incorrectly passing only a 2-digit year
5143 instead of "year - 1900" into the png_convert_from_struct_tm() function,
5144 but this is not under our control. The libpng documentation has always
5145 stated that it works with 4-digit years, and the APIs have been
5148 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5149 integer to hold the year, and can hold years as large as 65535.
5151 zlib, upon which libpng depends, is also Y2K compliant. It contains
5152 no date-related code.
5155 Glenn Randers-Pehrson
5157 PNG Development Group
5161 Note about libpng version numbers:
5163 Due to various miscommunications, unforeseen code incompatibilities
5164 and occasional factors outside the authors' control, version numbering
5165 on the library has not always been consistent and straightforward.
5166 The following table summarizes matters since version 0.89c, which was
5167 the first widely used release:
5169 source png.h png.h shared-lib
5170 version string int version
5171 ------- ------ ----- ----------
5172 0.89c ("beta 3") 0.89 89 1.0.89
5173 0.90 ("beta 4") 0.90 90 0.90
5174 0.95 ("beta 5") 0.95 95 0.95
5175 0.96 ("beta 6") 0.96 96 0.96
5176 0.97b ("beta 7") 1.00.97 97 1.0.1
5177 0.97c 0.97 97 2.0.97
5180 0.99a-m 0.99 99 2.0.99
5182 1.0.0 1.0.0 100 2.1.0
5183 1.0.0 (from here on, the 100 2.1.0
5184 1.0.1 png.h string is 10001 2.1.0
5185 1.0.1a-e identical to the 10002 from here on, the
5186 1.0.2 source version) 10002 shared library is 2.V
5187 1.0.2a-b 10003 where V is the source
5188 1.0.1 10001 code version except as
5189 1.0.1a-e 10002 2.1.0.1a-e noted.
5191 1.0.2a-b 10003 2.1.0.2a-b
5193 1.0.3a-d 10004 2.1.0.3a-d
5195 1.0.4a-f 10005 2.1.0.4a-f
5196 1.0.5 (+ 2 patches) 10005 2.1.0.5
5197 1.0.5a-d 10006 2.1.0.5a-d
5198 1.0.5e-r 10100 2.1.0.5e-r
5199 1.0.5s-v 10006 2.1.0.5s-v
5200 1.0.6 (+ 3 patches) 10006 2.1.0.6
5201 1.0.6d-g 10007 2.1.0.6d-g
5204 1.0.6j 10007 2.1.0.6j
5205 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5206 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5207 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5208 1.0.7 1 10007 2.1.0.7
5209 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5210 1.0.8rc1 1 10008 2.1.0.8rc1
5211 1.0.8 1 10008 2.1.0.8
5212 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5213 1.0.9rc1 1 10009 2.1.0.9rc1
5214 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5215 1.0.9rc2 1 10009 2.1.0.9rc2
5216 1.0.9 1 10009 2.1.0.9
5217 1.0.10beta1 1 10010 2.1.0.10beta1
5218 1.0.10rc1 1 10010 2.1.0.10rc1
5219 1.0.10 1 10010 2.1.0.10
5220 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5221 1.0.11rc1 1 10011 2.1.0.11rc1
5222 1.0.11 1 10011 2.1.0.11
5223 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5224 1.0.12rc1 2 10012 2.1.0.12rc1
5225 1.0.12 2 10012 2.1.0.12
5226 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5227 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5228 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5229 1.2.0rc1 3 10200 3.1.2.0rc1
5230 1.2.0 3 10200 3.1.2.0
5231 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5232 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5233 1.2.1 3 10201 3.1.2.1
5234 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5235 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5236 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5237 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5238 1.0.13 10 10013 10.so.0.1.0.13
5239 1.2.2 12 10202 12.so.0.1.2.2
5240 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5241 1.2.3 12 10203 12.so.0.1.2.3
5242 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5243 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5244 1.0.14 10 10014 10.so.0.1.0.14
5245 1.2.4 13 10204 12.so.0.1.2.4
5246 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5247 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5248 1.0.15 10 10015 10.so.0.1.0.15
5249 1.2.5 13 10205 12.so.0.1.2.5
5250 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5251 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5252 1.0.16 10 10016 10.so.0.1.0.16
5253 1.2.6 13 10206 12.so.0.1.2.6
5254 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5255 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5256 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5257 1.0.17 10 10017 12.so.0.1.0.17
5258 1.2.7 13 10207 12.so.0.1.2.7
5259 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5260 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5261 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5262 1.0.18 10 10018 12.so.0.1.0.18
5263 1.2.8 13 10208 12.so.0.1.2.8
5264 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5265 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5266 1.2.9rc1 13 10209 12.so.0.9[.0]
5267 1.2.9 13 10209 12.so.0.9[.0]
5268 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5269 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5270 1.2.10 13 10210 12.so.0.10[.0]
5271 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5272 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5273 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5274 1.2.11 13 10211 12.so.0.11[.0]
5275 1.2.12 13 10212 12.so.0.12[.0]
5276 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5277 1.2.13 13 10213 12.so.0.13[.0]
5278 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5279 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5280 1.4.0rc01 14 10400 14.so.14.0[.0]
5281 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5282 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5283 1.4.0 14 10400 14.so.14.0[.0]
5284 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5285 1.4.1rc01 14 10401 14.so.14.1[.0]
5286 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5287 1.4.1 14 10401 14.so.14.1[.0]
5288 1.4.2 14 10402 14.so.14.2[.0]
5289 1.4.3 14 10403 14.so.14.3[.0]
5290 1.4.4 14 10404 14.so.14.4[.0]
5291 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5292 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5293 1.5.0 15 10500 15.so.15.0[.0]
5294 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5295 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5296 1.5.1 15 10501 15.so.15.1[.0]
5297 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5298 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5299 1.5.2 15 10502 15.so.15.2[.0]
5300 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5301 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5302 1.5.3beta11 15 10503 15.so.15.3[.0]
5304 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5305 1.5.4rc01 15 10504 15.so.15.4[.0]
5306 1.5.4 15 10504 15.so.15.4[.0]
5307 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5308 1.5.5rc01 15 10505 15.so.15.5[.0]
5309 1.5.5 15 10505 15.so.15.5[.0]
5310 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5311 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5312 1.5.6 15 10506 15.so.15.6[.0]
5313 1.5.7beta01-05 15 10507 15.so.15.7[.0]
5314 1.5.7rc01-03 15 10507 15.so.15.7[.0]
5315 1.5.7 15 10507 15.so.15.7[.0]
5316 1.5.8beta01 15 10508 15.so.15.8[.0]
5317 1.5.8rc01 15 10508 15.so.15.8[.0]
5318 1.5.8 15 10508 15.so.15.8[.0]
5319 1.5.9beta01-02 15 10509 15.so.15.9[.0]
5320 1.5.9rc01 15 10509 15.so.15.9[.0]
5321 1.5.9 15 10509 15.so.15.9[.0]
5322 1.5.10beta01-05 15 10510 15.so.15.10[.0]
5323 1.5.10 15 10510 15.so.15.10[.0]
5324 1.5.11beta01 15 10511 15.so.15.11[.0]
5325 1.5.11rc01-05 15 10511 15.so.15.11[.0]
5326 1.5.11 15 10511 15.so.15.11[.0]
5327 1.5.12 15 10512 15.so.15.12[.0]
5328 1.5.13beta01-02 15 10513 15.so.15.13[.0]
5329 1.5.13rc01 15 10513 15.so.15.13[.0]
5330 1.5.13 15 10513 15.so.15.13[.0]
5331 1.5.14beta01-08 15 10514 15.so.15.14[.0]
5332 1.5.14rc01-03 15 10514 15.so.15.14[.0]
5333 1.5.14 15 10514 15.so.15.14[.0]
5335 Henceforth the source version will match the shared-library minor
5336 and patch numbers; the shared-library major version number will be
5337 used for changes in backward compatibility, as it is intended. The
5338 PNG_PNGLIB_VER macro, which is not used within libpng but is available
5339 for applications, is an unsigned integer of the form xyyzz corresponding
5340 to the source version x.y.z (leading zeros in y and z). Beta versions
5341 were given the previous public release number plus a letter, until
5342 version 1.0.6j; from then on they were given the upcoming public
5343 release number plus "betaNN" or "rcN".
5346 .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5351 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5352 http://www.libpng.org/pub/png
5357 (generally) at the same location as
5361 ftp://ftp.info-zip.org/pub/infozip/zlib
5364 .IR PNG specification: RFC 2083
5366 (generally) at the same location as
5370 ftp://ds.internic.net/rfc/rfc2083.txt
5372 or (as a W3C Recommendation) at
5374 http://www.w3.org/TR/REC-png.html
5377 In the case of any inconsistency between the PNG specification
5378 and this library, the specification takes precedence.
5381 This man page: Glenn Randers-Pehrson
5382 <glennrp at users.sourceforge.net>
5384 The contributing authors would like to thank all those who helped
5385 with testing, bug fixes, and patience. This wouldn't have been
5386 possible without all of you.
5388 Thanks to Frank J. T. Wojcik for helping with the documentation.
5390 Libpng version 1.5.14 - January 24, 2013:
5391 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5392 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5394 Supported by the PNG development group
5396 png-mng-implement at lists.sf.net
5397 (subscription required; visit
5398 png-mng-implement at lists.sourceforge.net (subscription required; visit
5399 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5402 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5404 (This copy of the libpng notices is provided for your convenience. In case of
5405 any discrepancy between this copy and the notices in the file png.h that is
5406 included in the libpng distribution, the latter shall prevail.)
5408 If you modify libpng you may insert additional notices immediately following
5411 This code is released under the libpng license.
5413 libpng versions 1.2.6, August 15, 2004, through 1.5.14, January 24, 2013, are
5414 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5415 distributed according to the same disclaimer and license as libpng-1.2.5
5416 with the following individual added to the list of Contributing Authors
5420 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5421 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5422 distributed according to the same disclaimer and license as libpng-1.0.6
5423 with the following individuals added to the list of Contributing Authors
5425 Simon-Pierre Cadieux
5429 and with the following additions to the disclaimer:
5431 There is no warranty against interference with your
5432 enjoyment of the library or against infringement.
5433 There is no warranty that our efforts or the library
5434 will fulfill any of your particular purposes or needs.
5435 This library is provided with all faults, and the entire
5436 risk of satisfactory quality, performance, accuracy, and
5437 effort is with the user.
5439 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5440 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5441 Distributed according to the same disclaimer and license as libpng-0.96,
5442 with the following individuals added to the list of Contributing Authors:
5445 Glenn Randers-Pehrson
5448 libpng versions 0.89, June 1996, through 0.96, May 1997, are
5449 Copyright (c) 1996, 1997 Andreas Dilger
5450 Distributed according to the same disclaimer and license as libpng-0.88,
5451 with the following individuals added to the list of Contributing Authors:
5460 libpng versions 0.5, May 1995, through 0.88, January 1996, are
5461 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
5463 For the purposes of this copyright and license, "Contributing Authors"
5464 is defined as the following set of individuals:
5472 The PNG Reference Library is supplied "AS IS". The Contributing Authors
5473 and Group 42, Inc. disclaim all warranties, expressed or implied,
5474 including, without limitation, the warranties of merchantability and of
5475 fitness for any purpose. The Contributing Authors and Group 42, Inc.
5476 assume no liability for direct, indirect, incidental, special, exemplary,
5477 or consequential damages, which may result from the use of the PNG
5478 Reference Library, even if advised of the possibility of such damage.
5480 Permission is hereby granted to use, copy, modify, and distribute this
5481 source code, or portions hereof, for any purpose, without fee, subject
5482 to the following restrictions:
5484 1. The origin of this source code must not be misrepresented.
5486 2. Altered versions must be plainly marked as such and
5487 must not be misrepresented as being the original source.
5489 3. This Copyright notice may not be removed or altered from
5490 any source or altered source distribution.
5492 The Contributing Authors and Group 42, Inc. specifically permit, without
5493 fee, and encourage the use of this source code as a component to
5494 supporting the PNG file format in commercial products. If you use this
5495 source code in a product, acknowledgment is not required but would be
5499 A "png_get_copyright" function is available, for convenient use in "about"
5502 printf("%s",png_get_copyright(NULL));
5504 Also, the PNG logo (in PNG format, of course) is supplied in the
5505 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
5507 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
5508 certification mark of the Open Source Initiative.
5510 Glenn Randers-Pehrson
5511 glennrp at users.sourceforge.net