1 .TH LIBPNG 3 "March 31, 2011"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.5.2
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
19 \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
23 \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
27 \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
31 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
35 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
39 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
43 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
47 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
51 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
55 \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
59 \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
63 \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
67 \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
71 \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
75 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
79 \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
83 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
87 \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
91 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
95 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
103 \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
107 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
111 \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
115 \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
119 \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
123 \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
127 \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
131 \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
137 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
141 \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
145 \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
149 \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
153 \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
157 \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
161 \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
165 \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
169 \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
173 \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
177 \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
181 \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
185 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
189 \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
193 \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
197 \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
201 \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
205 \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
209 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
213 \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
217 \fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
221 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
225 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
229 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
233 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
237 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
241 \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
245 \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
249 \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
253 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
257 \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
261 \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
265 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
269 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
273 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
277 \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
281 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
283 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
287 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
291 \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
295 \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
299 \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
303 \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
307 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
311 \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
315 \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
319 \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
323 \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
327 \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
331 \fB/* This function is really an inline macro. \fI*/
333 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
337 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
341 \fB/* This function is really an inline macro. \fI*/
343 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
347 \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
351 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
355 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
359 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
363 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
367 \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
371 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
375 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
379 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
383 \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
387 \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
391 \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
395 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
399 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
403 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
407 \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
411 \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
415 \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
419 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
423 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
427 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
431 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
435 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
439 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
443 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
447 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
451 \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
455 \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
459 \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
463 \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
467 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
471 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
475 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
479 \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
483 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
487 \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
491 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
495 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
499 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
503 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
507 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
511 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
515 \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
519 \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
523 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
527 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
531 \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
535 \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
539 \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
543 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
547 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
551 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
555 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
559 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
563 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
567 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
571 \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
575 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
579 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
583 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
587 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
591 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
595 \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
599 \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
603 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
607 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
611 \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
615 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
619 \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
623 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
627 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
631 \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
635 \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
639 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
643 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
647 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
651 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
655 \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
659 \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
663 \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
667 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
671 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
675 \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
679 \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
683 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
687 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
691 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
695 \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
699 \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
703 \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
707 \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
711 \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
715 \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
719 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
723 \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
727 \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
731 \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
735 \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
739 \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
743 \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
747 \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
751 \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
755 \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
759 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
763 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
767 \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
771 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
775 \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
779 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
783 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
787 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
791 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
795 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
799 \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
803 \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
807 \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
811 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
815 \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
819 \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
823 \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
827 \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
831 \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
835 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
839 \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
843 \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
847 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
851 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
855 \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
859 \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
863 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
867 \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
871 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
875 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
879 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
883 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
887 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
891 \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
895 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
899 \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
903 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
907 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
911 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
918 library supports encoding, decoding, and various manipulations of
919 the Portable Network Graphics (PNG) format image files. It uses the
922 Following is a copy of the libpng-manual.txt file that accompanies libpng.
924 libpng-manual.txt - A description on how to use and modify libpng
926 libpng version 1.5.2 - March 31, 2011
927 Updated and distributed by Glenn Randers-Pehrson
928 <glennrp at users.sourceforge.net>
929 Copyright (c) 1998-2011 Glenn Randers-Pehrson
931 This document is released under the libpng license.
932 For conditions of distribution and use, see the disclaimer
937 libpng versions 0.97, January 1998, through 1.5.2 - March 31, 2011
938 Updated and distributed by Glenn Randers-Pehrson
939 Copyright (c) 1998-2011 Glenn Randers-Pehrson
941 libpng 1.0 beta 6 version 0.96 May 28, 1997
942 Updated and distributed by Andreas Dilger
943 Copyright (c) 1996, 1997 Andreas Dilger
945 libpng 1.0 beta 2 - version 0.88 January 26, 1996
946 For conditions of distribution and use, see copyright
947 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
948 Schalnat, Group 42, Inc.
950 Updated/rewritten per request in the libpng FAQ
951 Copyright (c) 1995, 1996 Frank J. T. Wojcik
952 December 18, 1995 & January 20, 1996
956 This file describes how to use and modify the PNG reference library
957 (known as libpng) for your own use. There are five sections to this
958 file: introduction, structures, reading, writing, and modification and
959 configuration notes for various special platforms. In addition to this
960 file, example.c is a good starting point for using the library, as
961 it is heavily commented and should include everything most people
962 will need. We assume that libpng is already installed; see the
963 INSTALL file for instructions on how to install libpng.
965 For examples of libpng usage, see the files "example.c", "pngtest.c",
966 and the files in the "contrib" directory, all of which are included in
967 the libpng distribution.
969 Libpng was written as a companion to the PNG specification, as a way
970 of reducing the amount of time and effort it takes to support the PNG
971 file format in application programs.
973 The PNG specification (second edition), November 2003, is available as
974 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
975 <http://www.w3.org/TR/2003/REC-PNG-20031110/
976 The W3C and ISO documents have identical technical content.
978 The PNG-1.2 specification is available at
979 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
980 to the PNG specification (second edition) but has some additional material.
982 The PNG-1.0 specification is available
983 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
984 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
986 Some additional chunks are described in the special-purpose public chunks
987 documents at <http://www.libpng.org/pub/png/documents/>.
990 about PNG, and the latest version of libpng, can be found at the PNG home
991 page, <http://www.libpng.org/pub/png/>.
993 Most users will not have to modify the library significantly; advanced
994 users may want to modify it more. All attempts were made to make it as
995 complete as possible, while keeping the code easy to understand.
996 Currently, this library only supports C. Support for other languages
999 Libpng has been designed to handle multiple sessions at one time,
1000 to be easily modifiable, to be portable to the vast majority of
1001 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
1002 to use. The ultimate goal of libpng is to promote the acceptance of
1003 the PNG file format in whatever way possible. While there is still
1004 work to be done (see the TODO file), libpng should cover the
1005 majority of the needs of its users.
1007 Libpng uses zlib for its compression and decompression of PNG files.
1008 Further information about zlib, and the latest version of zlib, can
1009 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
1010 The zlib compression utility is a general purpose utility that is
1011 useful for more than PNG files, and can be used without libpng.
1012 See the documentation delivered with zlib for more details.
1013 You can usually find the source files for the zlib utility wherever you
1014 find the libpng source files.
1016 Libpng is thread safe, provided the threads are using different
1017 instances of the structures. Each thread should have its own
1018 png_struct and png_info instances, and thus its own image.
1019 Libpng does not protect itself against two threads using the
1020 same instance of a structure.
1024 There are two main structures that are important to libpng, png_struct
1025 and png_info. Both are internal structures that are no longer exposed
1026 in the libpng interface (as of libpng 1.5.0).
1028 The png_info structure is designed to provide information about the
1029 PNG file. At one time, the fields of png_info were intended to be
1030 directly accessible to the user. However, this tended to cause problems
1031 with applications using dynamically loaded libraries, and as a result
1032 a set of interface functions for png_info (the png_get_*() and png_set_*()
1033 functions) was developed.
1035 The png_struct structure is the object used by the library to decode a
1036 single image. As of 1.5.0 this structure is also not exposed.
1038 Almost all libpng APIs require a pointer to a png_struct as the first argument.
1039 Many (in particular the png_set and png_get APIs) also require a pointer
1040 to png_info as the second argument. Some application visible macros
1041 defined in png.h designed for basic data access (reading and writing
1042 integers in the PNG format) break this rule, but it's almost always safe
1043 to assume that a (png_struct*) has to be passed to call an API function.
1045 The png.h header file is an invaluable reference for programming with libpng.
1046 And while I'm on the topic, make sure you include the libpng header file:
1052 The png.h header file defines a number of integral types used by the
1053 APIs. Most of these are fairly obvious; for example types corresponding
1054 to integers of particular sizes and types for passing color values.
1056 One exception is how non-integral numbers are handled. For application
1057 convenience most APIs that take such numbers have C (double) arguments,
1058 however internally PNG, and libpng, use 32 bit signed integers and encode
1059 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
1060 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
1061 which is simply (png_int_32).
1063 All APIs that take (double) arguments also have an matching API that
1064 takes the corresponding fixed point integer arguments. The fixed point
1065 API has the same name as the floating point one with _fixed appended.
1066 The actual range of values permitted in the APIs is frequently less than
1067 the full range of (png_fixed_point) (-21474 to +21474). When APIs require
1068 a non-negative argument the type is recorded as png_uint_32 above. Consult
1069 the header file and the text below for more information.
1071 Special care must be take with sCAL chunk handling because the chunk itself
1072 uses non-integral values encoded as strings containing decimal floating point
1073 numbers. See the comments in the header file.
1077 The main header file function declarations are frequently protected by C
1078 preprocessing directives of the form:
1080 #ifdef PNG_feature_SUPPORTED
1084 The library can be built without support for these APIs, although a
1085 standard build will have all implemented APIs. Application programs
1086 should check the feature macros before using an API for maximum
1087 portability. From libpng 1.5.0 the feature macros set during the build
1088 of libpng are recorded in the header file "pnglibconf.h" and this file
1089 is always included by png.h.
1091 If you don't need to change the library configuration from the default skip to
1092 the next section ("Reading").
1094 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
1095 of the build project files in the 'projects' directory simply copy
1096 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
1097 systems do not permit easy auto-configuration of the library - they only
1098 support the default configuration.
1100 The easiest way to make minor changes to the libpng configuration when
1101 auto-configuration is supported is to add definitions to the command line
1102 using (typically) CPPFLAGS. For example:
1104 CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
1106 will change the internal libpng math implementation for gamma correction and
1107 other arithmetic calculations to fixed point, avoiding the need for fast
1108 floating point support. The result can be seen in the generated pnglibconf.h -
1109 make sure it contains the changed feature macro setting.
1111 If you need to make more extensive configuration changes - more than one or two
1112 feature macro settings - you can either add -DPNG_USER_CONFIG to the build
1113 command line and put a list of feature macro settings in pngusr.h or you can set
1114 DFA_XTRA (a makefile variable) to a file containing the same information in the
1115 form of 'option' settings.
1117 A. Changing pnglibconf.h
1119 A variety of methods exist to build libpng. Not all of these support
1120 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
1121 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
1123 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt and changing
1124 the lines defining the supported features, paying very close attention to the
1125 'option' information in scripts/pnglibconf.dfa that describes those features and
1126 their requirements. This is easy to get wrong.
1128 B. Configuration using DFA_XTRA
1130 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
1131 variant such as 'nawk' or 'gawk', is available. The configure build will
1132 automatically find an appropriate awk and build pnglibconf.h.
1133 scripts/pnglibconf.mak contains a set of make rules for doing the same thing if
1134 configure is not used, and many of the makefiles in the scripts directory use
1137 When rebuilding simply write new file containing changed options and set
1138 DFA_XTRA to the name of this file. This causes the build to append the new file
1139 to the end of scripts/pnglibconf.dfa. pngusr.dfa should contain lines of the
1144 This turns all optional features off. Include it at the start of pngusr.dfa to
1145 make it easier to build a minimal configuration. You will need to turn at least
1146 some features on afterward to enable either reading or writing code, or both.
1151 Enable or disable a single feature. This will automatically enable other
1152 features required by a feature that is turned on or disable other features that
1153 require a feature which is turned off. Conflicting settings will cause an error
1154 message to be emitted by awk.
1156 setting feature default value
1158 Changes the default value of setting 'feature' to 'value'. There are a small
1159 number of settings listed at the top of pnglibconf.h, they are documented in the
1160 source code. Most of these values have performance implications for the library
1161 but most of them have no visible effect on the API. Some can also be overridden
1164 C. Configuration using PNG_USR_CONFIG
1166 If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
1167 pngusr.h will automatically be included before the options in
1168 scripts/pnglibconf.dfa are processed. pngusr.h should contain only macro
1169 definitions turning features on or off or setting settings.
1171 Apart from the global setting "everything = off" all the options listed above
1172 can be set using macros in pngusr.h:
1174 #define PNG_feature_SUPPORTED
1180 #define PNG_NO_feature
1186 #define PNG_feature value
1190 setting feature default value
1192 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
1193 pngusr file you supply override the contents of scripts/pnglibconf.dfa
1195 If confusing or incomprehensible behavior results it is possible to
1196 examine the intermediate file pnglibconf.dfn to find the full set of
1197 dependency information for each setting and option. Simply locate the
1198 feature in the file and read the C comments that precede it.
1202 We'll now walk you through the possible functions to call when reading
1203 in a PNG file sequentially, briefly explaining the syntax and purpose
1204 of each one. See example.c and png.h for more detail. While
1205 progressive reading is covered in the next section, you will still
1206 need some of the functions discussed in this section to read a PNG
1211 You will want to do the I/O initialization(*) before you get into libpng,
1212 so if it doesn't work, you don't have much to undo. Of course, you
1213 will also want to insure that you are, in fact, dealing with a PNG
1214 file. Libpng provides a simple check to see if a file is a PNG file.
1215 To use it, pass in the first 1 to 8 bytes of the file to the function
1216 png_sig_cmp(), and it will return 0 (false) if the bytes match the
1217 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
1218 Of course, the more bytes you pass in, the greater the accuracy of the
1221 If you are intending to keep the file pointer open for use in libpng,
1222 you must ensure you don't read more than 8 bytes from the beginning
1223 of the file, and you also have to make a call to png_set_sig_bytes_read()
1224 with the number of bytes you read from the beginning. Libpng will
1225 then only check the bytes (if any) that your program didn't read.
1227 (*): If you are not using the standard I/O functions, you will need
1228 to replace them with custom functions. See the discussion under
1232 FILE *fp = fopen(file_name, "rb");
1238 fread(header, 1, number, fp);
1239 is_png = !png_sig_cmp(header, 0, number);
1247 Next, png_struct and png_info need to be allocated and initialized. In
1248 order to ensure that the size of these structures is correct even with a
1249 dynamically linked libpng, there are functions to initialize and
1250 allocate the structures. We also pass the library version, optional
1251 pointers to error handling functions, and a pointer to a data struct for
1252 use by the error functions, if necessary (the pointer and functions can
1253 be NULL if the default error handlers are to be used). See the section
1254 on Changes to Libpng below regarding the old initialization functions.
1255 The structure allocation functions quietly return NULL if they fail to
1256 create the structure, so your application should check for that.
1258 png_structp png_ptr = png_create_read_struct
1259 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1260 user_error_fn, user_warning_fn);
1265 png_infop info_ptr = png_create_info_struct(png_ptr);
1269 png_destroy_read_struct(&png_ptr,
1270 (png_infopp)NULL, (png_infopp)NULL);
1274 png_infop end_info = png_create_info_struct(png_ptr);
1278 png_destroy_read_struct(&png_ptr, &info_ptr,
1283 If you want to use your own memory allocation routines,
1284 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
1285 png_create_read_struct_2() instead of png_create_read_struct():
1287 png_structp png_ptr = png_create_read_struct_2
1288 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1289 user_error_fn, user_warning_fn, (png_voidp)
1290 user_mem_ptr, user_malloc_fn, user_free_fn);
1292 The error handling routines passed to png_create_read_struct()
1293 and the memory alloc/free routines passed to png_create_struct_2()
1294 are only necessary if you are not using the libpng supplied error
1295 handling and memory alloc/free functions.
1297 When libpng encounters an error, it expects to longjmp back
1298 to your routine. Therefore, you will need to call setjmp and pass
1299 your png_jmpbuf(png_ptr). If you read the file from different
1300 routines, you will need to update the jmpbuf field every time you enter
1301 a new routine that will call a png_*() function.
1303 See your documentation of setjmp/longjmp for your compiler for more
1304 information on setjmp/longjmp. See the discussion on libpng error
1305 handling in the Customizing Libpng section below for more information
1306 on the libpng error handling. If an error occurs, and libpng longjmp's
1307 back to your setjmp, you will want to call png_destroy_read_struct() to
1310 if (setjmp(png_jmpbuf(png_ptr)))
1312 png_destroy_read_struct(&png_ptr, &info_ptr,
1318 If you would rather avoid the complexity of setjmp/longjmp issues,
1319 you can compile libpng with PNG_NO_SETJMP, in which case
1320 errors will result in a call to PNG_ABORT() which defaults to abort().
1322 You can #define PNG_ABORT() to a function that does something
1323 more useful than abort(), as long as your function does not
1326 Now you need to set up the input code. The default for libpng is to
1327 use the C function fread(). If you use this, you will need to pass a
1328 valid FILE * in the function png_init_io(). Be sure that the file is
1329 opened in binary mode. If you wish to handle reading data in another
1330 way, you need not call the png_init_io() function, but you must then
1331 implement the libpng I/O methods discussed in the Customizing Libpng
1334 png_init_io(png_ptr, fp);
1336 If you had previously opened the file and read any of the signature from
1337 the beginning in order to see if this was a PNG file, you need to let
1338 libpng know that there are some bytes missing from the start of the file.
1340 png_set_sig_bytes(png_ptr, number);
1342 You can change the zlib compression buffer size to be used while
1343 reading compressed data with
1345 png_set_compression_buffer_size(png_ptr, buffer_size);
1347 where the default size is 8192 bytes. Note that the buffer size
1348 is changed immediately and the buffer is reallocated immediately,
1349 instead of setting a flag to be acted upon later.
1351 If you want CRC errors to be handled in a different manner than
1354 png_set_crc_action(png_ptr, crit_action, ancil_action);
1356 The values for png_set_crc_action() say how libpng is to handle CRC errors in
1357 ancillary and critical chunks, and whether to use the data contained
1358 therein. Note that it is impossible to "discard" data in a critical
1361 Choices for (int) crit_action are
1362 PNG_CRC_DEFAULT 0 error/quit
1363 PNG_CRC_ERROR_QUIT 1 error/quit
1364 PNG_CRC_WARN_USE 3 warn/use data
1365 PNG_CRC_QUIET_USE 4 quiet/use data
1366 PNG_CRC_NO_CHANGE 5 use the current value
1368 Choices for (int) ancil_action are
1369 PNG_CRC_DEFAULT 0 error/quit
1370 PNG_CRC_ERROR_QUIT 1 error/quit
1371 PNG_CRC_WARN_DISCARD 2 warn/discard data
1372 PNG_CRC_WARN_USE 3 warn/use data
1373 PNG_CRC_QUIET_USE 4 quiet/use data
1374 PNG_CRC_NO_CHANGE 5 use the current value
1376 .SS Setting up callback code
1378 You can set up a callback function to handle any unknown chunks in the
1379 input stream. You must supply the function
1381 read_chunk_callback(png_structp png_ptr,
1382 png_unknown_chunkp chunk);
1384 /* The unknown chunk structure contains your
1385 chunk data, along with similar data for any other
1392 /* Note that libpng has already taken care of
1395 /* put your code here. Search for your chunk in the
1396 unknown chunk structure, process it, and return one
1397 of the following: */
1399 return (-n); /* chunk had an error */
1400 return (0); /* did not recognize */
1401 return (n); /* success */
1404 (You can give your function another name that you like instead of
1405 "read_chunk_callback")
1407 To inform libpng about your function, use
1409 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1410 read_chunk_callback);
1412 This names not only the callback function, but also a user pointer that
1413 you can retrieve with
1415 png_get_user_chunk_ptr(png_ptr);
1417 If you call the png_set_read_user_chunk_fn() function, then all unknown
1418 chunks will be saved when read, in case your callback function will need
1419 one or more of them. This behavior can be changed with the
1420 png_set_keep_unknown_chunks() function, described below.
1422 At this point, you can set up a callback function that will be
1423 called after each row has been read, which you can use to control
1424 a progress meter or the like. It's demonstrated in pngtest.c.
1425 You must supply a function
1427 void read_row_callback(png_structp png_ptr,
1428 png_uint_32 row, int pass);
1430 /* put your code here */
1433 (You can give it another name that you like instead of "read_row_callback")
1435 To inform libpng about your function, use
1437 png_set_read_status_fn(png_ptr, read_row_callback);
1439 When this function is called the row has already been completely processed and
1440 the 'row' and 'pass' refer to the next row to be handled. For the
1441 non-interlaced case the row that was just handled is simply one less than the
1442 passed in row number, and pass will always be 0. For the interlaced case the
1443 same applies unless the row value is 0, in which case the row just handled was
1444 the last one from one of the preceding passes. Because interlacing may skip a
1445 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1446 need to know what the last pass is record (row,pass) from the callback and use
1447 the last recorded value each time.
1449 As with the user transform you can find the output row using the
1450 PNG_ROW_FROM_PASS_ROW macro.
1452 .SS Unknown-chunk handling
1454 Now you get to set the way the library processes unknown chunks in the
1455 input PNG stream. Both known and unknown chunks will be read. Normal
1456 behavior is that known chunks will be parsed into information in
1457 various info_ptr members while unknown chunks will be discarded. This
1458 behavior can be wasteful if your application will never use some known
1459 chunk types. To change this, you can call:
1461 png_set_keep_unknown_chunks(png_ptr, keep,
1462 chunk_list, num_chunks);
1463 keep - 0: default unknown chunk handling
1464 1: ignore; do not keep
1465 2: keep only if safe-to-copy
1466 3: keep even if unsafe-to-copy
1468 You can use these definitions:
1469 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1470 PNG_HANDLE_CHUNK_NEVER 1
1471 PNG_HANDLE_CHUNK_IF_SAFE 2
1472 PNG_HANDLE_CHUNK_ALWAYS 3
1474 chunk_list - list of chunks affected (a byte string,
1475 five bytes per chunk, NULL or '\0' if
1478 num_chunks - number of chunks affected; if 0, all
1479 unknown chunks are affected. If nonzero,
1480 only the chunks in the list are affected
1482 Unknown chunks declared in this way will be saved as raw data onto a
1483 list of png_unknown_chunk structures. If a chunk that is normally
1484 known to libpng is named in the list, it will be handled as unknown,
1485 according to the "keep" directive. If a chunk is named in successive
1486 instances of png_set_keep_unknown_chunks(), the final instance will
1487 take precedence. The IHDR and IEND chunks should not be named in
1488 chunk_list; if they are, libpng will process them normally anyway.
1490 Here is an example of the usage of png_set_keep_unknown_chunks(),
1491 where the private "vpAg" chunk will later be processed by a user chunk
1494 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1496 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1497 png_byte unused_chunks[]=
1499 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1500 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1501 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1502 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1503 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1504 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1510 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1511 /* ignore all unknown chunks: */
1512 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1514 /* except for vpAg: */
1515 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1517 /* also ignore unused known chunks: */
1518 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1519 (int)sizeof(unused_chunks)/5);
1524 The PNG specification allows the width and height of an image to be as
1525 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1526 Since very few applications really need to process such large images,
1527 we have imposed an arbitrary 1-million limit on rows and columns.
1528 Larger images will be rejected immediately with a png_error() call. If
1529 you wish to override this limit, you can use
1531 png_set_user_limits(png_ptr, width_max, height_max);
1533 to set your own limits, or use width_max = height_max = 0x7fffffffL
1534 to allow all valid dimensions (libpng may reject some very large images
1535 anyway because of potential buffer overflow conditions).
1537 You should put this statement after you create the PNG structure and
1538 before calling png_read_info(), png_read_png(), or png_process_data().
1539 If you need to retrieve the limits that are being applied, use
1541 width_max = png_get_user_width_max(png_ptr);
1542 height_max = png_get_user_height_max(png_ptr);
1544 The PNG specification sets no limit on the number of ancillary chunks
1545 allowed in a PNG datastream. You can impose a limit on the total number
1546 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1548 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1550 where 0x7fffffffL means unlimited. You can retrieve this limit with
1552 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1554 This limit also applies to the number of buffers that can be allocated
1555 by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1557 You can also set a limit on the amount of memory that a compressed chunk
1558 other than IDAT can occupy, with
1560 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1562 and you can retrieve the limit with
1564 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1566 Any chunks that would cause either of these limits to be exceeded will
1569 .SS The high-level read interface
1571 At this point there are two ways to proceed; through the high-level
1572 read interface, or through a sequence of low-level read operations.
1573 You can use the high-level interface if (a) you are willing to read
1574 the entire image into memory, and (b) the input transformations
1575 you want to do are limited to the following set:
1577 PNG_TRANSFORM_IDENTITY No transformation
1578 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1580 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1581 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1583 PNG_TRANSFORM_PACKSWAP Change order of packed
1585 PNG_TRANSFORM_EXPAND Perform set_expand()
1586 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1587 PNG_TRANSFORM_SHIFT Normalize pixels to the
1589 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1591 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1593 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1595 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1596 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1597 to RGB (or GA to RGBA)
1599 (This excludes setting a background color, doing gamma transformation,
1600 quantizing, and setting filler.) If this is the case, simply do this:
1602 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1604 where png_transforms is an integer containing the bitwise OR of some
1605 set of transformation flags. This call is equivalent to png_read_info(),
1606 followed the set of transformations indicated by the transform mask,
1607 then png_read_image(), and finally png_read_end().
1609 (The final parameter of this call is not yet used. Someday it might point
1610 to transformation parameters required by some future input transform.)
1612 You must use png_transforms and not call any png_set_transform() functions
1613 when you use png_read_png().
1615 After you have called png_read_png(), you can retrieve the image data
1618 row_pointers = png_get_rows(png_ptr, info_ptr);
1620 where row_pointers is an array of pointers to the pixel data for each row:
1622 png_bytep row_pointers[height];
1624 If you know your image size and pixel size ahead of time, you can allocate
1625 row_pointers prior to calling png_read_png() with
1627 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1629 "Image is too tall to process in memory");
1631 if (width > PNG_UINT_32_MAX/pixel_size)
1633 "Image is too wide to process in memory");
1635 row_pointers = png_malloc(png_ptr,
1636 height*png_sizeof(png_bytep));
1638 for (int i=0; i<height, i++)
1639 row_pointers[i]=NULL; /* security precaution */
1641 for (int i=0; i<height, i++)
1642 row_pointers[i]=png_malloc(png_ptr,
1645 png_set_rows(png_ptr, info_ptr, &row_pointers);
1647 Alternatively you could allocate your image in one big block and define
1648 row_pointers[i] to point into the proper places in your block.
1650 If you use png_set_rows(), the application is responsible for freeing
1651 row_pointers (and row_pointers[i], if they were separately allocated).
1653 If you don't allocate row_pointers ahead of time, png_read_png() will
1654 do it, and it'll be free'ed by libpng when you call png_destroy_*().
1656 .SS The low-level read interface
1658 If you are going the low-level route, you are now ready to read all
1659 the file information up to the actual image data. You do this with a
1660 call to png_read_info().
1662 png_read_info(png_ptr, info_ptr);
1664 This will process all chunks up to but not including the image data.
1666 .SS Querying the info structure
1668 Functions are used to get the information from the info_ptr once it
1669 has been read. Note that these fields may not be completely filled
1670 in until png_read_end() has read the chunk data following the image.
1672 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1673 &bit_depth, &color_type, &interlace_type,
1674 &compression_type, &filter_method);
1676 width - holds the width of the image
1677 in pixels (up to 2^31).
1679 height - holds the height of the image
1680 in pixels (up to 2^31).
1682 bit_depth - holds the bit depth of one of the
1683 image channels. (valid values are
1684 1, 2, 4, 8, 16 and depend also on
1685 the color_type. See also
1686 significant bits (sBIT) below).
1688 color_type - describes which color/alpha channels
1691 (bit depths 1, 2, 4, 8, 16)
1692 PNG_COLOR_TYPE_GRAY_ALPHA
1694 PNG_COLOR_TYPE_PALETTE
1695 (bit depths 1, 2, 4, 8)
1698 PNG_COLOR_TYPE_RGB_ALPHA
1701 PNG_COLOR_MASK_PALETTE
1702 PNG_COLOR_MASK_COLOR
1703 PNG_COLOR_MASK_ALPHA
1705 interlace_type - (PNG_INTERLACE_NONE or
1706 PNG_INTERLACE_ADAM7)
1708 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1711 filter_method - (must be PNG_FILTER_TYPE_BASE
1712 for PNG 1.0, and can also be
1713 PNG_INTRAPIXEL_DIFFERENCING if
1714 the PNG datastream is embedded in
1715 a MNG-1.0 datastream)
1717 Any or all of interlace_type, compression_type, or
1718 filter_method can be NULL if you are
1719 not interested in their values.
1721 Note that png_get_IHDR() returns 32-bit data into
1722 the application's width and height variables.
1723 This is an unsafe situation if these are 16-bit
1724 variables. In such situations, the
1725 png_get_image_width() and png_get_image_height()
1726 functions described below are safer.
1728 width = png_get_image_width(png_ptr,
1731 height = png_get_image_height(png_ptr,
1734 bit_depth = png_get_bit_depth(png_ptr,
1737 color_type = png_get_color_type(png_ptr,
1740 interlace_type = png_get_interlace_type(png_ptr,
1743 compression_type = png_get_compression_type(png_ptr,
1746 filter_method = png_get_filter_type(png_ptr,
1749 channels = png_get_channels(png_ptr, info_ptr);
1751 channels - number of channels of info for the
1752 color type (valid values are 1 (GRAY,
1753 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1754 4 (RGB_ALPHA or RGB + filler byte))
1756 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1758 rowbytes - number of bytes needed to hold a row
1760 signature = png_get_signature(png_ptr, info_ptr);
1762 signature - holds the signature read from the
1763 file (if any). The data is kept in
1764 the same offset it would be if the
1765 whole signature were read (i.e. if an
1766 application had already read in 4
1767 bytes of signature before starting
1768 libpng, the remaining 4 bytes would
1769 be in signature[4] through signature[7]
1770 (see png_set_sig_bytes())).
1772 These are also important, but their validity depends on whether the chunk
1773 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1774 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1775 data has been read, or zero if it is missing. The parameters to the
1776 png_get_<chunk> are set directly if they are simple data types, or a
1777 pointer into the info_ptr is returned for any complex types.
1779 png_get_PLTE(png_ptr, info_ptr, &palette,
1782 palette - the palette for the file
1783 (array of png_color)
1785 num_palette - number of entries in the palette
1787 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1788 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1790 file_gamma - the gamma at which the file is
1791 written (PNG_INFO_gAMA)
1793 int_file_gamma - 100,000 times the gamma at which the
1796 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1798 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
1799 The presence of the sRGB chunk
1800 means that the pixel data is in the
1801 sRGB color space. This chunk also
1802 implies specific values of gAMA and
1805 png_get_iCCP(png_ptr, info_ptr, &name,
1806 &compression_type, &profile, &proflen);
1808 name - The profile name.
1810 compression_type - The compression type; always
1811 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1812 You may give NULL to this argument to
1815 profile - International Color Consortium color
1816 profile data. May contain NULs.
1818 proflen - length of profile data in bytes.
1820 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1822 sig_bit - the number of significant bits for
1823 (PNG_INFO_sBIT) each of the gray,
1824 red, green, and blue channels,
1825 whichever are appropriate for the
1826 given color type (png_color_16)
1828 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1829 &num_trans, &trans_color);
1831 trans_alpha - array of alpha (transparency)
1832 entries for palette (PNG_INFO_tRNS)
1834 num_trans - number of transparent entries
1837 trans_color - graylevel or color sample values of
1838 the single transparent color for
1839 non-paletted images (PNG_INFO_tRNS)
1841 png_get_hIST(png_ptr, info_ptr, &hist);
1844 hist - histogram of palette (array of
1847 png_get_tIME(png_ptr, info_ptr, &mod_time);
1849 mod_time - time image was last modified
1852 png_get_bKGD(png_ptr, info_ptr, &background);
1854 background - background color (PNG_VALID_bKGD)
1855 valid 16-bit red, green and blue
1856 values, regardless of color_type
1858 num_comments = png_get_text(png_ptr, info_ptr,
1859 &text_ptr, &num_text);
1861 num_comments - number of comments
1863 text_ptr - array of png_text holding image
1866 text_ptr[i].compression - type of compression used
1867 on "text" PNG_TEXT_COMPRESSION_NONE
1868 PNG_TEXT_COMPRESSION_zTXt
1869 PNG_ITXT_COMPRESSION_NONE
1870 PNG_ITXT_COMPRESSION_zTXt
1872 text_ptr[i].key - keyword for comment. Must contain
1875 text_ptr[i].text - text comments for current
1876 keyword. Can be empty.
1878 text_ptr[i].text_length - length of text string,
1879 after decompression, 0 for iTXt
1881 text_ptr[i].itxt_length - length of itxt string,
1882 after decompression, 0 for tEXt/zTXt
1884 text_ptr[i].lang - language of comment (empty
1885 string for unknown).
1887 text_ptr[i].lang_key - keyword in UTF-8
1888 (empty string for unknown).
1890 Note that the itxt_length, lang, and lang_key
1891 members of the text_ptr structure only exist
1892 when the library is built with iTXt chunk support.
1894 num_text - number of comments (same as
1895 num_comments; you can put NULL here
1896 to avoid the duplication)
1898 Note while png_set_text() will accept text, language,
1899 and translated keywords that can be NULL pointers, the
1900 structure returned by png_get_text will always contain
1901 regular zero-terminated C strings. They might be
1902 empty strings but they will never be NULL pointers.
1904 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1907 num_spalettes - number of sPLT chunks read.
1909 palette_ptr - array of palette structures holding
1910 contents of one or more sPLT chunks
1913 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1916 offset_x - positive offset from the left edge
1919 offset_y - positive offset from the top edge
1922 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1924 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1927 res_x - pixels/unit physical resolution in
1930 res_y - pixels/unit physical resolution in
1933 unit_type - PNG_RESOLUTION_UNKNOWN,
1934 PNG_RESOLUTION_METER
1936 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1939 unit - physical scale units (an integer)
1941 width - width of a pixel in physical scale units
1943 height - height of a pixel in physical scale units
1944 (width and height are doubles)
1946 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1949 unit - physical scale units (an integer)
1951 width - width of a pixel in physical scale units
1953 height - height of a pixel in physical scale units
1954 (width and height are strings like "2.54")
1956 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1957 info_ptr, &unknowns)
1959 unknowns - array of png_unknown_chunk
1960 structures holding unknown chunks
1962 unknowns[i].name - name of unknown chunk
1964 unknowns[i].data - data of unknown chunk
1966 unknowns[i].size - size of unknown chunk's data
1968 unknowns[i].location - position of chunk in file
1970 The value of "i" corresponds to the order in which the
1971 chunks were read from the PNG file or inserted with the
1972 png_set_unknown_chunks() function.
1974 The data from the pHYs chunk can be retrieved in several convenient
1977 res_x = png_get_x_pixels_per_meter(png_ptr,
1980 res_y = png_get_y_pixels_per_meter(png_ptr,
1983 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1986 res_x = png_get_x_pixels_per_inch(png_ptr,
1989 res_y = png_get_y_pixels_per_inch(png_ptr,
1992 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1995 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1998 Each of these returns 0 [signifying "unknown"] if
1999 the data is not present or if res_x is 0;
2000 res_x_and_y is 0 if res_x != res_y
2002 Note that because of the way the resolutions are
2003 stored internally, the inch conversions won't
2004 come out to exactly even number. For example,
2005 72 dpi is stored as 0.28346 pixels/meter, and
2006 when this is retrieved it is 71.9988 dpi, so
2007 be sure to round the returned value appropriately
2008 if you want to display a reasonable-looking result.
2010 The data from the oFFs chunk can be retrieved in several convenient
2013 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2015 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2017 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2019 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2021 Each of these returns 0 [signifying "unknown" if both
2022 x and y are 0] if the data is not present or if the
2023 chunk is present but the unit is the pixel. The
2024 remark about inexact inch conversions applies here
2025 as well, because a value in inches can't always be
2026 converted to microns and back without some loss
2029 For more information, see the png_info definition in png.h and the
2030 PNG specification for chunk contents. Be careful with trusting
2031 rowbytes, as some of the transformations could increase the space
2032 needed to hold a row (expand, filler, gray_to_rgb, etc.).
2033 See png_read_update_info(), below.
2035 A quick word about text_ptr and num_text. PNG stores comments in
2036 keyword/text pairs, one pair per chunk, with no limit on the number
2037 of text chunks, and a 2^31 byte limit on their size. While there are
2038 suggested keywords, there is no requirement to restrict the use to these
2039 strings. It is strongly suggested that keywords and text be sensible
2040 to humans (that's the point), so don't use abbreviations. Non-printing
2041 symbols are not allowed. See the PNG specification for more details.
2042 There is also no requirement to have text after the keyword.
2044 Keywords should be limited to 79 Latin-1 characters without leading or
2045 trailing spaces, but non-consecutive spaces are allowed within the
2046 keyword. It is possible to have the same keyword any number of times.
2047 The text_ptr is an array of png_text structures, each holding a
2048 pointer to a language string, a pointer to a keyword and a pointer to
2049 a text string. The text string, language code, and translated
2050 keyword may be empty or NULL pointers. The keyword/text
2051 pairs are put into the array in the order that they are received.
2052 However, some or all of the text chunks may be after the image, so, to
2053 make sure you have read all the text chunks, don't mess with these
2054 until after you read the stuff after the image. This will be
2055 mentioned again below in the discussion that goes with png_read_end().
2057 .SS Input transformations
2059 After you've read the header information, you can set up the library
2060 to handle any special transformations of the image data. The various
2061 ways to transform the data will be described in the order that they
2062 should occur. This is important, as some of these change the color
2063 type and/or bit depth of the data, and some others only work on
2064 certain color types and bit depths. Even though each transformation
2065 checks to see if it has data that it can do something with, you should
2066 make sure to only enable a transformation if it will be valid for the
2067 data. For example, don't swap red and blue on grayscale data.
2069 The colors used for the background and transparency values should be
2070 supplied in the same format/depth as the current image data. They
2071 are stored in the same format/depth as the image data in a bKGD or tRNS
2072 chunk, so this is what libpng expects for this data. The colors are
2073 transformed to keep in sync with the image data when an application
2074 calls the png_read_update_info() routine (see below).
2076 Data will be decoded into the supplied row buffers packed into bytes
2077 unless the library has been told to transform it into another format.
2078 For example, 4 bit/pixel paletted or grayscale data will be returned
2079 2 pixels/byte with the leftmost pixel in the high-order bits of the
2080 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2081 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2082 is called to insert filler bytes, either before or after each RGB triplet.
2083 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2084 byte of the color value first, unless png_set_strip_16() is called to
2085 transform it to regular RGB RGB triplets, or png_set_filler() or
2086 png_set_add alpha() is called to insert filler bytes, either before or
2087 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2089 png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
2091 The following code transforms grayscale images of less than 8 to 8 bits,
2092 changes paletted images to RGB, and adds a full alpha channel if there is
2093 transparency information in a tRNS chunk. This is most useful on
2094 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2095 viewing application that wishes to treat all images in the same way.
2097 if (color_type == PNG_COLOR_TYPE_PALETTE)
2098 png_set_palette_to_rgb(png_ptr);
2100 if (png_get_valid(png_ptr, info_ptr,
2101 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2103 if (color_type == PNG_COLOR_TYPE_GRAY &&
2104 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2106 The first two functions are actually aliases for png_set_expand(), added
2107 in libpng version 1.0.4, with the function names expanded to improve code
2108 readability. In some future version they may actually do different
2111 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2112 added. It expands the sample depth without changing tRNS to alpha.
2114 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2115 png_set_expand(), however, the resultant channels have 16 bits rather than 8.
2116 Use this when the output color or gray channels are made linear to avoid fairly
2117 severe accuracy loss.
2120 png_set_expand_16(png_ptr);
2122 PNG can have files with 16 bits per channel. If you only can handle
2123 8 bits per channel, this will strip the pixels down to 8 bit.
2125 if (bit_depth == 16)
2126 png_set_strip_16(png_ptr);
2128 If, for some reason, you don't need the alpha channel on an image,
2129 and you want to remove it rather than combining it with the background
2130 (but the image author certainly had in mind that you *would* combine
2131 it with the background, so that's what you should probably do):
2133 if (color_type & PNG_COLOR_MASK_ALPHA)
2134 png_set_strip_alpha(png_ptr);
2136 See below for png_set_background(), which does the correct composition on a
2137 single opaque color. This is probably what you should do in all cases rather
2138 than use png_set_strip_alpha() - unless you know for sure that it is the wrong
2141 As of libpng version 1.5.2, almost all useful expansions are supported, the
2142 major ommissions are convertion of grayscale to indexed images (which can be
2143 done trivially in the application) and convertion of indexed to grayscale (which
2144 can be done by a trivial manipulation of the palette.)
2146 In the following table, the 01 means grayscale with depth<8, 31 means
2147 indexed with depth<8, other numerals represent the color type, "T" means
2148 the tRNS chunk is present, A means an alpha channel is present, and O
2149 means tRNS or alpha is present but all pixels in the image are opaque.
2151 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2153 01 - [G] - - - - - - - - - - - - -
2154 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2155 0 1 G + . . G G G G G G B B GB GB
2156 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2157 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2158 2 C P C C C + . . C - - CB CB B B
2159 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2160 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2161 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2162 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2163 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2164 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2165 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2166 6A CA PA CA C C A T tT PA P P C CBA + BA
2167 6O CA PBA CA C C A tT T PA P P CBA C BA +
2170 "+" identifies entries where 'from' and 'to' are the same.
2171 "-" means the transformation is not supported.
2172 "." means nothing is necessary (a tRNS chunk can just be ignored).
2173 "t" means the transformation is obtained by png_set_tRNS.
2174 "A" means the transformation is obtained by png_set_add_alpha().
2175 "X" means the transformation is obtained by png_set_expand().
2176 "1" means the transformation is obtained by
2177 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there
2178 is no transparency in the original or the final format).
2179 "C" means the transformation is obtained by png_set_gray_to_rgb().
2180 "G" means the transformation is obtained by png_set_rgb_to_gray() or
2182 "P" means the transformation is obtained by
2183 png_set_expand_palette_to_rgb().
2184 "p" means the transformation is obtained by png_set_packing().
2185 "Q" means the transformation is obtained by png_set_quantize().
2186 "T" means the transformation is obtained by png_set_tRNS_to_alpha().
2187 "B" means the transformation is obtained by png_set_background(), or
2190 When an entry has multiple transforms listed all are required to cause the
2191 right overall transformation. When two transforms are separated by a comma
2192 either will do the job. When transforms are enclosed in [] the transform should
2193 do the job but this is currently unimplemented - a different format will result
2194 if the suggested transformations are used.
2196 In PNG files, the alpha channel in an image
2197 is the level of opacity. If you need the alpha channel in an image to
2198 be the level of transparency instead of opacity, you can invert the
2199 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2200 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2201 images) is fully transparent, with
2203 png_set_invert_alpha(png_ptr);
2205 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2206 they can, resulting in, for example, 8 pixels per byte for 1 bit
2207 files. This code expands to 1 pixel per byte without changing the
2208 values of the pixels:
2211 png_set_packing(png_ptr);
2213 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2214 stored in a PNG image have been "scaled" or "shifted" up to the next
2215 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2216 to 8 bits/sample in the range [0, 255]). However, it is also possible
2217 to convert the PNG pixel data back to the original bit depth of the
2218 image. This call reduces the pixels back down to the original bit depth:
2220 png_color_8p sig_bit;
2222 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2223 png_set_shift(png_ptr, sig_bit);
2225 PNG files store 3-color pixels in red, green, blue order. This code
2226 changes the storage of the pixels to blue, green, red:
2228 if (color_type == PNG_COLOR_TYPE_RGB ||
2229 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2230 png_set_bgr(png_ptr);
2232 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2233 into 4 or 8 bytes for windowing systems that need them in this format:
2235 if (color_type == PNG_COLOR_TYPE_RGB)
2236 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2238 where "filler" is the 8 or 16-bit number to fill with, and the location is
2239 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2240 you want the filler before the RGB or after. This transformation
2241 does not affect images that already have full alpha channels. To add an
2242 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2243 will generate RGBA pixels.
2245 Note that png_set_filler() does not change the color type. If you want
2246 to do that, you can add a true alpha channel with
2248 if (color_type == PNG_COLOR_TYPE_RGB ||
2249 color_type == PNG_COLOR_TYPE_GRAY)
2250 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2252 where "filler" contains the alpha value to assign to each pixel.
2253 This function was added in libpng-1.2.7.
2255 If you are reading an image with an alpha channel, and you need the
2256 data as ARGB instead of the normal PNG format RGBA:
2258 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2259 png_set_swap_alpha(png_ptr);
2261 For some uses, you may want a grayscale image to be represented as
2262 RGB. This code will do that conversion:
2264 if (color_type == PNG_COLOR_TYPE_GRAY ||
2265 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2266 png_set_gray_to_rgb(png_ptr);
2268 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2271 if (color_type == PNG_COLOR_TYPE_RGB ||
2272 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2273 png_set_rgb_to_gray_fixed(png_ptr, error_action,
2274 int red_weight, int green_weight);
2276 error_action = 1: silently do the conversion
2278 error_action = 2: issue a warning if the original
2279 image has any pixel where
2280 red != green or red != blue
2282 error_action = 3: issue an error and abort the
2283 conversion if the original
2284 image has any pixel where
2285 red != green or red != blue
2287 red_weight: weight of red component times 100000
2289 green_weight: weight of green component times 100000
2290 If either weight is negative, default
2291 weights (21268, 71514) are used.
2293 If you have set error_action = 1 or 2, you can
2294 later check whether the image really was gray, after processing
2295 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2296 It will return a png_byte that is zero if the image was gray or
2297 1 if there were any non-gray pixels. bKGD and sBIT data
2298 will be silently converted to grayscale, using the green channel
2299 data, regardless of the error_action setting.
2301 With red_weight+green_weight<=100000,
2302 the normalized graylevel is computed:
2304 int rw = red_weight * 65536;
2305 int gw = green_weight * 65536;
2306 int bw = 65536 - (rw + gw);
2307 gray = (rw*red + gw*green + bw*blue)/65536;
2309 The default values approximate those recommended in the Charles
2310 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
2311 Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
2313 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2315 Libpng approximates this with integers scaled by 32768:
2317 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2319 The calculation is done in a linear colorspace, if the image gamma
2322 If you have a grayscale and you are using png_set_expand_gray_1_2_4_to_8(),
2323 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
2324 a higher bit-depth, you must either supply the background color as a gray
2325 value at the original file bit-depth (need_expand = 1) or else supply the
2326 background color as an RGB triplet at the final, expanded bit depth
2327 (need_expand = 0). Similarly, if you are reading a paletted image, you
2328 must either supply the background color as a palette index (need_expand = 1)
2329 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
2331 png_color_16 my_background;
2332 png_color_16p image_background;
2334 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2335 png_set_background(png_ptr, image_background,
2336 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
2338 png_set_background(png_ptr, &my_background,
2339 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
2341 The png_set_background() function tells libpng to composite images
2342 with alpha or simple transparency against the supplied background
2343 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2344 you may use this color, or supply another color more suitable for
2345 the current display (e.g., the background color from a web page). You
2346 need to tell libpng whether the color is in the gamma space of the
2347 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
2348 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
2349 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
2350 know why anyone would use this, but it's here).
2352 To properly display PNG images on any kind of system, the application needs
2353 to know what the display gamma is. Ideally, the user will know this, and
2354 the application will allow them to set it. One method of allowing the user
2355 to set the display gamma separately for each system is to check for a
2356 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
2359 Note that display_gamma is the overall gamma correction required to produce
2360 pleasing results, which depends on the lighting conditions in the surrounding
2361 environment. In a dim or brightly lit room, no compensation other than
2362 the physical gamma exponent of the monitor is needed, while in a dark room
2363 a slightly smaller exponent is better.
2365 double gamma, screen_gamma;
2367 if (/* We have a user-defined screen
2370 screen_gamma = user_defined_screen_gamma;
2373 /* One way that applications can share the same
2374 screen gamma value */
2375 else if ((gamma_str = getenv("SCREEN_GAMMA"))
2378 screen_gamma = (double)atof(gamma_str);
2381 /* If we don't have another value */
2384 screen_gamma = 2.2; /* A good guess for a
2385 PC monitor in a bright office or a dim room */
2387 screen_gamma = 2.0; /* A good guess for a
2388 PC monitor in a dark room */
2390 screen_gamma = 1.7 or 1.0; /* A good
2391 guess for Mac systems */
2394 The functions png_set_gamma() and its fixed point equivalent
2395 png_set_gamma_fixed() handle gamma transformations of the data.
2396 Pass both the file gamma and the current screen_gamma. If the file does
2397 not have a gamma value, you can pass one anyway if you have an idea what
2398 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
2399 that file gammas are inverted from screen gammas. See the discussions
2400 on gamma in the PNG specification for an excellent description of what
2401 gamma is, and why all applications should support it. It is strongly
2402 recommended that PNG viewers support gamma correction.
2404 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2405 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2408 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2410 If you need to reduce an RGB file to a paletted file, or if a paletted
2411 file has more entries then will fit on your screen, png_set_quantize()
2412 will do that. Note that this is a simple match quantization that merely
2413 finds the closest color available. This should work fairly well with
2414 optimized palettes, but fairly badly with linear color cubes. If you
2415 pass a palette that is larger then maximum_colors, the file will
2416 reduce the number of colors in the palette so it will fit into
2417 maximum_colors. If there is a histogram, it will use it to make
2418 more intelligent choices when reducing the palette. If there is no
2419 histogram, it may not do as good a job.
2421 if (color_type & PNG_COLOR_MASK_COLOR)
2423 if (png_get_valid(png_ptr, info_ptr,
2426 png_uint_16p histogram = NULL;
2428 png_get_hIST(png_ptr, info_ptr,
2430 png_set_quantize(png_ptr, palette, num_palette,
2431 max_screen_colors, histogram, 1);
2436 png_color std_color_cube[MAX_SCREEN_COLORS] =
2439 png_set_quantize(png_ptr, std_color_cube,
2440 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2445 PNG files describe monochrome as black being zero and white being one.
2446 The following code will reverse this (make black be one and white be
2449 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2450 png_set_invert_mono(png_ptr);
2452 This function can also be used to invert grayscale and gray-alpha images:
2454 if (color_type == PNG_COLOR_TYPE_GRAY ||
2455 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2456 png_set_invert_mono(png_ptr);
2458 PNG files store 16 bit pixels in network byte order (big-endian,
2459 ie. most significant bits first). This code changes the storage to the
2460 other way (little-endian, i.e. least significant bits first, the
2461 way PCs store them):
2463 if (bit_depth == 16)
2464 png_set_swap(png_ptr);
2466 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2467 need to change the order the pixels are packed into bytes, you can use:
2470 png_set_packswap(png_ptr);
2472 Finally, you can write your own transformation function if none of
2473 the existing ones meets your needs. This is done by setting a callback
2476 png_set_read_user_transform_fn(png_ptr,
2479 You must supply the function
2481 void read_transform_fn(png_structp png_ptr, png_row_infop
2482 row_info, png_bytep data)
2484 See pngtest.c for a working example. Your function will be called
2485 after all of the other transformations have been processed. Take care with
2486 interlaced images if you do the interlace yourself - the width of the row is the
2487 width in 'row_info', not the overall image width.
2489 If supported libpng provides two information routines that you can use to find
2490 where you are in processing the image:
2492 png_get_current_pass_number(png_structp png_ptr);
2493 png_get_current_row_number(png_structp png_ptr);
2495 Don't try using these outside a transform callback - firstly they are only
2496 supported if user transforms are supported, secondly they may well return
2497 unexpected results unless the row is actually being processed at the moment they
2501 images the value returned is the row in the input sub-image image. Use
2502 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2503 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2505 The discussion of interlace handling above contains more information on how to
2508 You can also set up a pointer to a user structure for use by your
2509 callback function, and you can inform libpng that your transform
2510 function will change the number of channels or bit depth with the
2513 png_set_user_transform_info(png_ptr, user_ptr,
2514 user_depth, user_channels);
2516 The user's application, not libpng, is responsible for allocating and
2517 freeing any memory required for the user structure.
2519 You can retrieve the pointer via the function
2520 png_get_user_transform_ptr(). For example:
2522 voidp read_user_transform_ptr =
2523 png_get_user_transform_ptr(png_ptr);
2525 The last thing to handle is interlacing; this is covered in detail below,
2526 but you must call the function here if you want libpng to handle expansion
2527 of the interlaced image.
2529 number_of_passes = png_set_interlace_handling(png_ptr);
2531 After setting the transformations, libpng can update your png_info
2532 structure to reflect any transformations you've requested with this
2533 call. This is most useful to update the info structure's rowbytes
2534 field so you can use it to allocate your image memory. This function
2535 will also update your palette with the correct screen_gamma and
2536 background if these have been given with the calls above.
2538 png_read_update_info(png_ptr, info_ptr);
2540 After you call png_read_update_info(), you can allocate any
2541 memory you need to hold the image. The row data is simply
2542 raw byte data for all forms of images. As the actual allocation
2543 varies among applications, no example will be given. If you
2544 are allocating one large chunk, you will need to build an
2545 array of pointers to each row, as it will be needed for some
2546 of the functions below.
2548 Remember: Before you call png_read_update_info(), the png_get_
2549 functions return the values corresponding to the original PNG image.
2550 After you call png_read_update_info the values refer to the image
2551 that libpng will output. Consequently you must call all the png_set_
2552 functions before you call png_read_update_info(). This is particularly
2553 important for png_set_interlace_handling() - if you are going to call
2554 png_read_update_info() you must call png_set_interlace_handling() before
2555 it unless you want to receive interlaced output.
2557 .SS Reading image data
2559 After you've allocated memory, you can read the image data.
2560 The simplest way to do this is in one function call. If you are
2561 allocating enough memory to hold the whole image, you can just
2562 call png_read_image() and libpng will read in all the image data
2563 and put it in the memory area supplied. You will need to pass in
2564 an array of pointers to each row.
2566 This function automatically handles interlacing, so you don't
2567 need to call png_set_interlace_handling() (unless you call
2568 png_read_update_info()) or call this function multiple times, or any
2569 of that other stuff necessary with png_read_rows().
2571 png_read_image(png_ptr, row_pointers);
2573 where row_pointers is:
2575 png_bytep row_pointers[height];
2577 You can point to void or char or whatever you use for pixels.
2579 If you don't want to read in the whole image at once, you can
2580 use png_read_rows() instead. If there is no interlacing (check
2581 interlace_type == PNG_INTERLACE_NONE), this is simple:
2583 png_read_rows(png_ptr, row_pointers, NULL,
2586 where row_pointers is the same as in the png_read_image() call.
2588 If you are doing this just one row at a time, you can do this with
2589 a single row_pointer instead of an array of row_pointers:
2591 png_bytep row_pointer = row;
2592 png_read_row(png_ptr, row_pointer, NULL);
2594 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2595 get somewhat harder. The only current (PNG Specification version 1.2)
2596 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2597 a somewhat complicated 2D interlace scheme, known as Adam7, that
2598 breaks down an image into seven smaller images of varying size, based
2599 on an 8x8 grid. This number is defined (from libpng 1.5) as
2600 PNG_INTERLACE_ADAM7_PASSES in png.h
2602 libpng can fill out those images or it can give them to you "as is".
2603 It is almost always better to have libpng handle the interlacing for you.
2604 If you want the images filled out, there are two ways to do that. The one
2605 mentioned in the PNG specification is to expand each pixel to cover
2606 those pixels that have not been read yet (the "rectangle" method).
2607 This results in a blocky image for the first pass, which gradually
2608 smooths out as more pixels are read. The other method is the "sparkle"
2609 method, where pixels are drawn only in their final locations, with the
2610 rest of the image remaining whatever colors they were initialized to
2611 before the start of the read. The first method usually looks better,
2612 but tends to be slower, as there are more pixels to put in the rows.
2614 If, as is likely, you want libpng to expand the images, call this before
2615 calling png_start_read_image() or png_read_update_info():
2617 if (interlace_type == PNG_INTERLACE_ADAM7)
2619 = png_set_interlace_handling(png_ptr);
2621 This will return the number of passes needed. Currently, this is seven,
2622 but may change if another interlace type is added. This function can be
2623 called even if the file is not interlaced, where it will return one pass.
2624 You then need to read the whole image 'number_of_passes' times. Each time
2625 will distribute the pixels from the current pass to the correct place in
2626 the output image, so you need to supply the same rows to png_read_rows in
2629 If you are not going to display the image after each pass, but are
2630 going to wait until the entire image is read in, use the sparkle
2631 effect. This effect is faster and the end result of either method
2632 is exactly the same. If you are planning on displaying the image
2633 after each pass, the "rectangle" effect is generally considered the
2636 If you only want the "sparkle" effect, just call png_read_rows() as
2637 normal, with the third parameter NULL. Make sure you make pass over
2638 the image number_of_passes times, and you don't change the data in the
2639 rows between calls. You can change the locations of the data, just
2640 not the data. Each pass only writes the pixels appropriate for that
2641 pass, and assumes the data from previous passes is still valid.
2643 png_read_rows(png_ptr, row_pointers, NULL,
2646 If you only want the first effect (the rectangles), do the same as
2647 before except pass the row buffer in the third parameter, and leave
2648 the second parameter NULL.
2650 png_read_rows(png_ptr, NULL, row_pointers,
2653 If you don't want libpng to handle the interlacing details, just call
2654 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2655 Each of the images is a valid image by itself, however you will almost
2656 certainly need to distribute the pixels from each sub-image to the
2657 correct place. This is where everything gets very tricky.
2659 If you want to retrieve the separate images you must pass the correct
2660 number of rows to each successive call of png_read_rows(). The calculation
2661 gets pretty complicated for small images, where some sub-images may
2662 not even exist because either their width or height ends up zero.
2663 libpng provides two macros to help you in 1.5 and later versions:
2665 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2666 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2668 Respectively these tell you the width and height of the sub-image
2669 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2670 this can be confusing because the specification refers to the same passes
2671 as 1 to 7! Be careful, you must check both the width and height before
2672 calling png_read_rows() and not call it for that pass if either is zero.
2674 You can, of course, read each sub-image row by row. If you want to
2675 produce optimal code to make a pixel-by-pixel transformation of an
2676 interlaced image this is the best approach; read each row of each pass,
2677 transform it, and write it out to a new interlaced image.
2679 If you want to de-interlace the image yourself libpng provides further
2680 macros to help that tell you where to place the pixels in the output image.
2681 Because the interlacing scheme is rectangular - sub-image pixels are always
2682 arranged on a rectangular grid - all you need to know for each pass is the
2683 starting column and row in the output image of the first pixel plus the
2684 spacing between each pixel. As of libpng 1.5 there are four macros to
2685 retrieve this information:
2687 png_uint_32 x = PNG_PASS_START_COL(pass);
2688 png_uint_32 y = PNG_PASS_START_ROW(pass);
2689 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2690 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2692 These allow you to write the obvious loop:
2694 png_uint_32 input_y = 0;
2695 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2697 while (output_y < output_image_height)
2699 png_uint_32 input_x = 0;
2700 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2702 while (output_x < output_image_width)
2704 image[output_y][output_x] =
2705 subimage[pass][input_y][input_x++];
2714 Notice that the steps between successive output rows and columns are
2715 returned as shifts. This is possible because the pixels in the subimages
2716 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2717 image. In practice you may need to directly calculate the output coordinate
2718 given an input coordinate. libpng provides two further macros for this
2721 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2722 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2724 Finally a pair of macros are provided to tell you if a particular image
2725 row or column appears in a given pass:
2727 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2728 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2730 Bear in mind that you will probably also need to check the width and height
2731 of the pass in addition to the above to be sure the pass even exists!
2733 With any luck you are convinced by now that you don't want to do your own
2734 interlace handling. In reality normally the only good reason for doing this
2735 is if you are processing PNG files on a pixel-by-pixel basis and don't want
2736 to load the whole file into memory when it is interlaced.
2738 libpng includes a test program, pngvalid, that illustrates reading and
2739 writing of interlaced images. If you can't get interlacing to work in your
2740 code and don't want to leave it to libpng (the recommended approach) see
2741 how pngvalid.c does it.
2743 .SS Finishing a sequential read
2745 After you are finished reading the image through the
2746 low-level interface, you can finish reading the file. If you are
2747 interested in comments or time, which may be stored either before or
2748 after the image data, you should pass the separate png_info struct if
2749 you want to keep the comments from before and after the image
2750 separate. If you are not interested, you can pass NULL.
2752 png_read_end(png_ptr, end_info);
2754 When you are done, you can free all memory allocated by libpng like this:
2756 png_destroy_read_struct(&png_ptr, &info_ptr,
2759 It is also possible to individually free the info_ptr members that
2760 point to libpng-allocated storage with the following function:
2762 png_free_data(png_ptr, info_ptr, mask, seq)
2764 mask - identifies data to be freed, a mask
2765 containing the bitwise OR of one or
2767 PNG_FREE_PLTE, PNG_FREE_TRNS,
2768 PNG_FREE_HIST, PNG_FREE_ICCP,
2769 PNG_FREE_PCAL, PNG_FREE_ROWS,
2770 PNG_FREE_SCAL, PNG_FREE_SPLT,
2771 PNG_FREE_TEXT, PNG_FREE_UNKN,
2772 or simply PNG_FREE_ALL
2774 seq - sequence number of item to be freed
2777 This function may be safely called when the relevant storage has
2778 already been freed, or has not yet been allocated, or was allocated
2779 by the user and not by libpng, and will in those cases do nothing.
2780 The "seq" parameter is ignored if only one item of the selected data
2781 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
2782 are allowed for the data type identified in the mask, such as text or
2783 sPLT, only the n'th item in the structure is freed, where n is "seq".
2785 The default behavior is only to free data that was allocated internally
2786 by libpng. This can be changed, so that libpng will not free the data,
2787 or so that it will free data that was allocated by the user with png_malloc()
2788 or png_zalloc() and passed in via a png_set_*() function, with
2790 png_data_freer(png_ptr, info_ptr, freer, mask)
2793 PNG_DESTROY_WILL_FREE_DATA
2794 PNG_SET_WILL_FREE_DATA
2795 PNG_USER_WILL_FREE_DATA
2797 mask - which data elements are affected
2798 same choices as in png_free_data()
2800 This function only affects data that has already been allocated.
2801 You can call this function after reading the PNG data but before calling
2802 any png_set_*() functions, to control whether the user or the png_set_*()
2803 function is responsible for freeing any existing data that might be present,
2804 and again after the png_set_*() functions to control whether the user
2805 or png_destroy_*() is supposed to free the data. When the user assumes
2806 responsibility for libpng-allocated data, the application must use
2807 png_free() to free it, and when the user transfers responsibility to libpng
2808 for data that the user has allocated, the user must have used png_malloc()
2809 or png_zalloc() to allocate it.
2811 If you allocated your row_pointers in a single block, as suggested above in
2812 the description of the high level read interface, you must not transfer
2813 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2814 because they would also try to free the individual row_pointers[i].
2816 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2817 separately, do not transfer responsibility for freeing text_ptr to libpng,
2818 because when libpng fills a png_text structure it combines these members with
2819 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2820 if you transfer responsibility for free'ing text_ptr from libpng to your
2821 application, your application must not separately free those members.
2823 The png_free_data() function will turn off the "valid" flag for anything
2824 it frees. If you need to turn the flag off for a chunk that was freed by
2825 your application instead of by libpng, you can use
2827 png_set_invalid(png_ptr, info_ptr, mask);
2829 mask - identifies the chunks to be made invalid,
2830 containing the bitwise OR of one or
2832 PNG_INFO_gAMA, PNG_INFO_sBIT,
2833 PNG_INFO_cHRM, PNG_INFO_PLTE,
2834 PNG_INFO_tRNS, PNG_INFO_bKGD,
2835 PNG_INFO_hIST, PNG_INFO_pHYs,
2836 PNG_INFO_oFFs, PNG_INFO_tIME,
2837 PNG_INFO_pCAL, PNG_INFO_sRGB,
2838 PNG_INFO_iCCP, PNG_INFO_sPLT,
2839 PNG_INFO_sCAL, PNG_INFO_IDAT
2841 For a more compact example of reading a PNG image, see the file example.c.
2843 .SS Reading PNG files progressively
2845 The progressive reader is slightly different then the non-progressive
2846 reader. Instead of calling png_read_info(), png_read_rows(), and
2847 png_read_end(), you make one call to png_process_data(), which calls
2848 callbacks when it has the info, a row, or the end of the image. You
2849 set up these callbacks with png_set_progressive_read_fn(). You don't
2850 have to worry about the input/output functions of libpng, as you are
2851 giving the library the data directly in png_process_data(). I will
2852 assume that you have read the section on reading PNG files above,
2853 so I will only highlight the differences (although I will show
2856 png_structp png_ptr;
2859 /* An example code fragment of how you would
2860 initialize the progressive reader in your
2863 initialize_png_reader()
2865 png_ptr = png_create_read_struct
2866 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2867 user_error_fn, user_warning_fn);
2872 info_ptr = png_create_info_struct(png_ptr);
2876 png_destroy_read_struct(&png_ptr,
2877 (png_infopp)NULL, (png_infopp)NULL);
2881 if (setjmp(png_jmpbuf(png_ptr)))
2883 png_destroy_read_struct(&png_ptr, &info_ptr,
2888 /* This one's new. You can provide functions
2889 to be called when the header info is valid,
2890 when each row is completed, and when the image
2891 is finished. If you aren't using all functions,
2892 you can specify NULL parameters. Even when all
2893 three functions are NULL, you need to call
2894 png_set_progressive_read_fn(). You can use
2895 any struct as the user_ptr (cast to a void pointer
2896 for the function call), and retrieve the pointer
2897 from inside the callbacks using the function
2899 png_get_progressive_ptr(png_ptr);
2901 which will return a void pointer, which you have
2902 to cast appropriately.
2904 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2905 info_callback, row_callback, end_callback);
2910 /* A code fragment that you call as you receive blocks
2913 process_data(png_bytep buffer, png_uint_32 length)
2915 if (setjmp(png_jmpbuf(png_ptr)))
2917 png_destroy_read_struct(&png_ptr, &info_ptr,
2922 /* This one's new also. Simply give it a chunk
2923 of data from the file stream (in order, of
2924 course). On machines with segmented memory
2925 models machines, don't give it any more than
2926 64K. The library seems to run fine with sizes
2927 of 4K. Although you can give it much less if
2928 necessary (I assume you can give it chunks of
2929 1 byte, I haven't tried less then 256 bytes
2930 yet). When this function returns, you may
2931 want to display any rows that were generated
2932 in the row callback if you don't already do
2935 png_process_data(png_ptr, info_ptr, buffer, length);
2937 /* At this point you can call png_process_data_skip if
2938 you want to handle data the library will skip yourself;
2939 it simply returns the number of bytes to skip (and stops
2940 libpng skipping that number of bytes on the next
2941 png_process_data call).
2945 /* This function is called (as set by
2946 png_set_progressive_read_fn() above) when enough data
2947 has been supplied so all of the header has been
2951 info_callback(png_structp png_ptr, png_infop info)
2953 /* Do any setup here, including setting any of
2954 the transformations mentioned in the Reading
2955 PNG files section. For now, you _must_ call
2956 either png_start_read_image() or
2957 png_read_update_info() after all the
2958 transformations are set (even if you don't set
2959 any). You may start getting rows before
2960 png_process_data() returns, so this is your
2961 last chance to prepare for that.
2963 This is where you turn on interlace handling,
2964 assuming you don't want to do it yourself.
2966 If you need to you can stop the processing of
2967 your original input data at this point by calling
2968 png_process_data_pause. This returns the number
2969 of unprocessed bytes from the last png_process_data
2970 call - it is up to you to ensure that the next call
2971 sees these bytes again. If you don't want to bother
2972 with this you can get libpng to cache the unread
2973 bytes by setting the 'save' parameter (see png.h) but
2974 then libpng will have to copy the data internally.
2978 /* This function is called when each row of image
2981 row_callback(png_structp png_ptr, png_bytep new_row,
2982 png_uint_32 row_num, int pass)
2984 /* If the image is interlaced, and you turned
2985 on the interlace handler, this function will
2986 be called for every row in every pass. Some
2987 of these rows will not be changed from the
2988 previous pass. When the row is not changed,
2989 the new_row variable will be NULL. The rows
2990 and passes are called in order, so you don't
2991 really need the row_num and pass, but I'm
2992 supplying them because it may make your life
2995 If you did not turn on interlace handling then
2996 the callback is called for each row of each
2997 sub-image when the image is interlaced. In this
2998 case 'row_num' is the row in the sub-image, not
2999 the row in the output image as it is in all other
3002 For the non-NULL rows of interlaced images when
3003 you have switched on libpng interlace handling,
3004 you must call png_progressive_combine_row()
3005 passing in the row and the old row. You can
3006 call this function for NULL rows (it will just
3007 return) and for non-interlaced images (it just
3008 does the memcpy for you) if it will make the
3009 code easier. Thus, you can just do this for
3010 all cases if you switch on interlace handling;
3013 png_progressive_combine_row(png_ptr, old_row,
3016 /* where old_row is what was displayed for
3017 previously for the row. Note that the first
3018 pass (pass == 0, really) will completely cover
3019 the old row, so the rows do not have to be
3020 initialized. After the first pass (and only
3021 for interlaced images), you will have to pass
3022 the current row, and the function will combine
3023 the old row and the new row.
3025 You can also call png_process_data_pause in this
3026 callback - see above.
3031 end_callback(png_structp png_ptr, png_infop info)
3033 /* This function is called after the whole image
3034 has been read, including any chunks after the
3035 image (up to and including the IEND). You
3036 will usually have the same info chunk as you
3037 had in the header, although some data may have
3038 been added to the comments and time fields.
3040 Most people won't do much here, perhaps setting
3041 a flag that marks the image as finished.
3049 Much of this is very similar to reading. However, everything of
3050 importance is repeated here, so you won't have to constantly look
3051 back up in the reading section to understand writing.
3055 You will want to do the I/O initialization before you get into libpng,
3056 so if it doesn't work, you don't have anything to undo. If you are not
3057 using the standard I/O functions, you will need to replace them with
3058 custom writing functions. See the discussion under Customizing libpng.
3060 FILE *fp = fopen(file_name, "wb");
3065 Next, png_struct and png_info need to be allocated and initialized.
3066 As these can be both relatively large, you may not want to store these
3067 on the stack, unless you have stack space to spare. Of course, you
3068 will want to check if they return NULL. If you are also reading,
3069 you won't want to name your read structure and your write structure
3070 both "png_ptr"; you can call them anything you like, such as
3071 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
3073 png_structp png_ptr = png_create_write_struct
3074 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3075 user_error_fn, user_warning_fn);
3080 png_infop info_ptr = png_create_info_struct(png_ptr);
3083 png_destroy_write_struct(&png_ptr,
3088 If you want to use your own memory allocation routines,
3089 define PNG_USER_MEM_SUPPORTED and use
3090 png_create_write_struct_2() instead of png_create_write_struct():
3092 png_structp png_ptr = png_create_write_struct_2
3093 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3094 user_error_fn, user_warning_fn, (png_voidp)
3095 user_mem_ptr, user_malloc_fn, user_free_fn);
3097 After you have these structures, you will need to set up the
3098 error handling. When libpng encounters an error, it expects to
3099 longjmp() back to your routine. Therefore, you will need to call
3100 setjmp() and pass the png_jmpbuf(png_ptr). If you
3101 write the file from different routines, you will need to update
3102 the png_jmpbuf(png_ptr) every time you enter a new routine that will
3103 call a png_*() function. See your documentation of setjmp/longjmp
3104 for your compiler for more information on setjmp/longjmp. See
3105 the discussion on libpng error handling in the Customizing Libpng
3106 section below for more information on the libpng error handling.
3108 if (setjmp(png_jmpbuf(png_ptr)))
3110 png_destroy_write_struct(&png_ptr, &info_ptr);
3117 If you would rather avoid the complexity of setjmp/longjmp issues,
3118 you can compile libpng with PNG_NO_SETJMP, in which case
3119 errors will result in a call to PNG_ABORT() which defaults to abort().
3121 You can #define PNG_ABORT() to a function that does something
3122 more useful than abort(), as long as your function does not
3125 Now you need to set up the output code. The default for libpng is to
3126 use the C function fwrite(). If you use this, you will need to pass a
3127 valid FILE * in the function png_init_io(). Be sure that the file is
3128 opened in binary mode. Again, if you wish to handle writing data in
3129 another way, see the discussion on libpng I/O handling in the Customizing
3130 Libpng section below.
3132 png_init_io(png_ptr, fp);
3134 If you are embedding your PNG into a datastream such as MNG, and don't
3135 want libpng to write the 8-byte signature, or if you have already
3136 written the signature in your application, use
3138 png_set_sig_bytes(png_ptr, 8);
3140 to inform libpng that it should not write a signature.
3144 At this point, you can set up a callback function that will be
3145 called after each row has been written, which you can use to control
3146 a progress meter or the like. It's demonstrated in pngtest.c.
3147 You must supply a function
3149 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3152 /* put your code here */
3155 (You can give it another name that you like instead of "write_row_callback")
3157 To inform libpng about your function, use
3159 png_set_write_status_fn(png_ptr, write_row_callback);
3161 When this function is called the row has already been completely processed and
3162 it has also been written out. The 'row' and 'pass' refer to the next row to be
3164 non-interlaced case the row that was just handled is simply one less than the
3165 passed in row number, and pass will always be 0. For the interlaced case the
3166 same applies unless the row value is 0, in which case the row just handled was
3167 the last one from one of the preceding passes. Because interlacing may skip a
3168 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3169 need to know what the last pass is record (row,pass) from the callback and use
3170 the last recorded value each time.
3172 As with the user transform you can find the output row using the
3173 PNG_ROW_FROM_PASS_ROW macro.
3175 You now have the option of modifying how the compression library will
3176 run. The following functions are mainly for testing, but may be useful
3177 in some cases, like if you need to write PNG files extremely fast and
3178 are willing to give up some compression, or if you want to get the
3179 maximum possible compression at the expense of slower writing. If you
3180 have no special needs in this area, let the library do what it wants by
3181 not calling this function at all, as it has been tuned to deliver a good
3182 speed/compression ratio. The second parameter to png_set_filter() is
3183 the filter method, for which the only valid values are 0 (as of the
3184 July 1999 PNG specification, version 1.2) or 64 (if you are writing
3185 a PNG datastream that is to be embedded in a MNG datastream). The third
3186 parameter is a flag that indicates which filter type(s) are to be tested
3187 for each scanline. See the PNG specification for details on the specific
3191 /* turn on or off filtering, and/or choose
3192 specific filters. You can use either a single
3193 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3194 or more PNG_FILTER_NAME masks.
3196 png_set_filter(png_ptr, 0,
3197 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3198 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3199 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3200 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3201 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3204 If an application wants to start and stop using particular filters during
3205 compression, it should start out with all of the filters (to ensure that
3206 the previous row of pixels will be stored in case it's needed later),
3207 and then add and remove them after the start of compression.
3209 If you are writing a PNG datastream that is to be embedded in a MNG
3210 datastream, the second parameter can be either 0 or 64.
3212 The png_set_compression_*() functions interface to the zlib compression
3213 library, and should mostly be ignored unless you really know what you are
3214 doing. The only generally useful call is png_set_compression_level()
3215 which changes how much time zlib spends on trying to compress the image
3216 data. See the Compression Library (zlib.h and algorithm.txt, distributed
3217 with zlib) for details on the compression levels.
3221 /* set the zlib compression level */
3222 png_set_compression_level(png_ptr,
3223 Z_BEST_COMPRESSION);
3225 /* set other zlib parameters */
3226 png_set_compression_mem_level(png_ptr, 8);
3227 png_set_compression_strategy(png_ptr,
3228 Z_DEFAULT_STRATEGY);
3229 png_set_compression_window_bits(png_ptr, 15);
3230 png_set_compression_method(png_ptr, 8);
3231 png_set_compression_buffer_size(png_ptr, 8192)
3233 extern PNG_EXPORT(void,png_set_zbuf_size)
3235 .SS Setting the contents of info for output
3237 You now need to fill in the png_info structure with all the data you
3238 wish to write before the actual image. Note that the only thing you
3239 are allowed to write after the image is the text chunks and the time
3240 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3241 the latest PNG specification for more information on that. If you
3242 wish to write them before the image, fill them in now, and flag that
3243 data as being valid. If you want to wait until after the data, don't
3244 fill them until png_write_end(). For all the fields in png_info and
3245 their data types, see png.h. For explanations of what the fields
3246 contain, see the PNG specification.
3248 Some of the more important parts of the png_info are:
3250 png_set_IHDR(png_ptr, info_ptr, width, height,
3251 bit_depth, color_type, interlace_type,
3252 compression_type, filter_method)
3254 width - holds the width of the image
3255 in pixels (up to 2^31).
3257 height - holds the height of the image
3258 in pixels (up to 2^31).
3260 bit_depth - holds the bit depth of one of the
3262 (valid values are 1, 2, 4, 8, 16
3263 and depend also on the
3264 color_type. See also significant
3267 color_type - describes which color/alpha
3268 channels are present.
3270 (bit depths 1, 2, 4, 8, 16)
3271 PNG_COLOR_TYPE_GRAY_ALPHA
3273 PNG_COLOR_TYPE_PALETTE
3274 (bit depths 1, 2, 4, 8)
3277 PNG_COLOR_TYPE_RGB_ALPHA
3280 PNG_COLOR_MASK_PALETTE
3281 PNG_COLOR_MASK_COLOR
3282 PNG_COLOR_MASK_ALPHA
3284 interlace_type - PNG_INTERLACE_NONE or
3287 compression_type - (must be
3288 PNG_COMPRESSION_TYPE_DEFAULT)
3290 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3291 or, if you are writing a PNG to
3292 be embedded in a MNG datastream,
3294 PNG_INTRAPIXEL_DIFFERENCING)
3296 If you call png_set_IHDR(), the call must appear before any of the
3297 other png_set_*() functions, because they might require access to some of
3298 the IHDR settings. The remaining png_set_*() functions can be called
3301 If you wish, you can reset the compression_type, interlace_type, or
3302 filter_method later by calling png_set_IHDR() again; if you do this, the
3303 width, height, bit_depth, and color_type must be the same in each call.
3305 png_set_PLTE(png_ptr, info_ptr, palette,
3308 palette - the palette for the file
3309 (array of png_color)
3310 num_palette - number of entries in the palette
3312 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3313 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3315 file_gamma - the gamma at which the image was
3316 created (PNG_INFO_gAMA)
3318 int_file_gamma - 100,000 times the gamma at which
3319 the image was created
3321 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3323 srgb_intent - the rendering intent
3324 (PNG_INFO_sRGB) The presence of
3325 the sRGB chunk means that the pixel
3326 data is in the sRGB color space.
3327 This chunk also implies specific
3328 values of gAMA and cHRM. Rendering
3329 intent is the CSS-1 property that
3330 has been defined by the International
3332 (http://www.color.org).
3334 PNG_sRGB_INTENT_SATURATION,
3335 PNG_sRGB_INTENT_PERCEPTUAL,
3336 PNG_sRGB_INTENT_ABSOLUTE, or
3337 PNG_sRGB_INTENT_RELATIVE.
3340 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3343 srgb_intent - the rendering intent
3344 (PNG_INFO_sRGB) The presence of the
3345 sRGB chunk means that the pixel
3346 data is in the sRGB color space.
3347 This function also causes gAMA and
3348 cHRM chunks with the specific values
3349 that are consistent with sRGB to be
3352 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3355 name - The profile name.
3357 compression_type - The compression type; always
3358 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3359 You may give NULL to this argument to
3362 profile - International Color Consortium color
3363 profile data. May contain NULs.
3365 proflen - length of profile data in bytes.
3367 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3369 sig_bit - the number of significant bits for
3370 (PNG_INFO_sBIT) each of the gray, red,
3371 green, and blue channels, whichever are
3372 appropriate for the given color type
3375 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3376 num_trans, trans_color);
3378 trans_alpha - array of alpha (transparency)
3379 entries for palette (PNG_INFO_tRNS)
3381 trans_color - graylevel or color sample values
3382 (in order red, green, blue) of the
3383 single transparent color for
3384 non-paletted images (PNG_INFO_tRNS)
3386 num_trans - number of transparent entries
3389 png_set_hIST(png_ptr, info_ptr, hist);
3391 hist - histogram of palette (array of
3392 png_uint_16) (PNG_INFO_hIST)
3394 png_set_tIME(png_ptr, info_ptr, mod_time);
3396 mod_time - time image was last modified
3399 png_set_bKGD(png_ptr, info_ptr, background);
3401 background - background color (PNG_VALID_bKGD)
3403 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3405 text_ptr - array of png_text holding image
3408 text_ptr[i].compression - type of compression used
3409 on "text" PNG_TEXT_COMPRESSION_NONE
3410 PNG_TEXT_COMPRESSION_zTXt
3411 PNG_ITXT_COMPRESSION_NONE
3412 PNG_ITXT_COMPRESSION_zTXt
3413 text_ptr[i].key - keyword for comment. Must contain
3415 text_ptr[i].text - text comments for current
3416 keyword. Can be NULL or empty.
3417 text_ptr[i].text_length - length of text string,
3418 after decompression, 0 for iTXt
3419 text_ptr[i].itxt_length - length of itxt string,
3420 after decompression, 0 for tEXt/zTXt
3421 text_ptr[i].lang - language of comment (NULL or
3423 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3424 or empty for unknown).
3425 Note that the itxt_length, lang, and lang_key
3426 members of the text_ptr structure only exist
3427 when the library is built with iTXt chunk support.
3429 num_text - number of comments
3431 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3434 palette_ptr - array of png_sPLT_struct structures
3435 to be added to the list of palettes
3436 in the info structure.
3437 num_spalettes - number of palette structures to be
3440 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3443 offset_x - positive offset from the left
3446 offset_y - positive offset from the top
3449 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3451 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3454 res_x - pixels/unit physical resolution
3457 res_y - pixels/unit physical resolution
3460 unit_type - PNG_RESOLUTION_UNKNOWN,
3461 PNG_RESOLUTION_METER
3463 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3465 unit - physical scale units (an integer)
3467 width - width of a pixel in physical scale units
3469 height - height of a pixel in physical scale units
3470 (width and height are doubles)
3472 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3474 unit - physical scale units (an integer)
3476 width - width of a pixel in physical scale units
3478 height - height of a pixel in physical scale units
3479 (width and height are strings like "2.54")
3481 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3484 unknowns - array of png_unknown_chunk
3485 structures holding unknown chunks
3486 unknowns[i].name - name of unknown chunk
3487 unknowns[i].data - data of unknown chunk
3488 unknowns[i].size - size of unknown chunk's data
3489 unknowns[i].location - position to write chunk in file
3490 0: do not write chunk
3491 PNG_HAVE_IHDR: before PLTE
3492 PNG_HAVE_PLTE: before IDAT
3493 PNG_AFTER_IDAT: after IDAT
3495 The "location" member is set automatically according to
3496 what part of the output file has already been written.
3497 You can change its value after calling png_set_unknown_chunks()
3498 as demonstrated in pngtest.c. Within each of the "locations",
3499 the chunks are sequenced according to their position in the
3500 structure (that is, the value of "i", which is the order in which
3501 the chunk was either read from the input file or defined with
3502 png_set_unknown_chunks).
3504 A quick word about text and num_text. text is an array of png_text
3505 structures. num_text is the number of valid structures in the array.
3506 Each png_text structure holds a language code, a keyword, a text value,
3507 and a compression type.
3509 The compression types have the same valid numbers as the compression
3510 types of the image data. Currently, the only valid number is zero.
3511 However, you can store text either compressed or uncompressed, unlike
3512 images, which always have to be compressed. So if you don't want the
3513 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3514 Because tEXt and zTXt chunks don't have a language field, if you
3515 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3516 any language code or translated keyword will not be written out.
3518 Until text gets around 1000 bytes, it is not worth compressing it.
3519 After the text has been written out to the file, the compression type
3520 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3521 so that it isn't written out again at the end (in case you are calling
3522 png_write_end() with the same struct).
3524 The keywords that are given in the PNG Specification are:
3526 Title Short (one line) title or
3529 Author Name of image's creator
3531 Description Description of image (possibly long)
3533 Copyright Copyright notice
3535 Creation Time Time of original image creation
3536 (usually RFC 1123 format, see below)
3538 Software Software used to create the image
3540 Disclaimer Legal disclaimer
3542 Warning Warning of nature of content
3544 Source Device used to create the image
3546 Comment Miscellaneous comment; conversion
3547 from other image format
3549 The keyword-text pairs work like this. Keywords should be short
3550 simple descriptions of what the comment is about. Some typical
3551 keywords are found in the PNG specification, as is some recommendations
3552 on keywords. You can repeat keywords in a file. You can even write
3553 some text before the image and some after. For example, you may want
3554 to put a description of the image before the image, but leave the
3555 disclaimer until after, so viewers working over modem connections
3556 don't have to wait for the disclaimer to go over the modem before
3557 they start seeing the image. Finally, keywords should be full
3558 words, not abbreviations. Keywords and text are in the ISO 8859-1
3559 (Latin-1) character set (a superset of regular ASCII) and can not
3560 contain NUL characters, and should not contain control or other
3561 unprintable characters. To make the comments widely readable, stick
3562 with basic ASCII, and avoid machine specific character set extensions
3563 like the IBM-PC character set. The keyword must be present, but
3564 you can leave off the text string on non-compressed pairs.
3565 Compressed pairs must have a text string, as only the text string
3566 is compressed anyway, so the compression would be meaningless.
3568 PNG supports modification time via the png_time structure. Two
3569 conversion routines are provided, png_convert_from_time_t() for
3570 time_t and png_convert_from_struct_tm() for struct tm. The
3571 time_t routine uses gmtime(). You don't have to use either of
3572 these, but if you wish to fill in the png_time structure directly,
3573 you should provide the time in universal time (GMT) if possible
3574 instead of your local time. Note that the year number is the full
3575 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3576 that months start with 1.
3578 If you want to store the time of the original image creation, you should
3579 use a plain tEXt chunk with the "Creation Time" keyword. This is
3580 necessary because the "creation time" of a PNG image is somewhat vague,
3581 depending on whether you mean the PNG file, the time the image was
3582 created in a non-PNG format, a still photo from which the image was
3583 scanned, or possibly the subject matter itself. In order to facilitate
3584 machine-readable dates, it is recommended that the "Creation Time"
3585 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3586 although this isn't a requirement. Unlike the tIME chunk, the
3587 "Creation Time" tEXt chunk is not expected to be automatically changed
3588 by the software. To facilitate the use of RFC 1123 dates, a function
3589 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
3590 time to an RFC 1123 format string.
3592 .SS Writing unknown chunks
3594 You can use the png_set_unknown_chunks function to queue up chunks
3595 for writing. You give it a chunk name, raw data, and a size; that's
3596 all there is to it. The chunks will be written by the next following
3597 png_write_info_before_PLTE, png_write_info, or png_write_end function.
3598 Any chunks previously read into the info structure's unknown-chunk
3599 list will also be written out in a sequence that satisfies the PNG
3600 specification's ordering rules.
3602 .SS The high-level write interface
3604 At this point there are two ways to proceed; through the high-level
3605 write interface, or through a sequence of low-level write operations.
3606 You can use the high-level interface if your image data is present
3607 in the info structure. All defined output
3608 transformations are permitted, enabled by the following masks.
3610 PNG_TRANSFORM_IDENTITY No transformation
3611 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3612 PNG_TRANSFORM_PACKSWAP Change order of packed
3614 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3615 PNG_TRANSFORM_SHIFT Normalize pixels to the
3617 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3619 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3621 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3623 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
3624 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3626 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3628 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3631 If you have valid image data in the info structure (you can use
3632 png_set_rows() to put image data in the info structure), simply do this:
3634 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3636 where png_transforms is an integer containing the bitwise OR of some set of
3637 transformation flags. This call is equivalent to png_write_info(),
3638 followed the set of transformations indicated by the transform mask,
3639 then png_write_image(), and finally png_write_end().
3641 (The final parameter of this call is not yet used. Someday it might point
3642 to transformation parameters required by some future output transform.)
3644 You must use png_transforms and not call any png_set_transform() functions
3645 when you use png_write_png().
3647 .SS The low-level write interface
3649 If you are going the low-level route instead, you are now ready to
3650 write all the file information up to the actual image data. You do
3651 this with a call to png_write_info().
3653 png_write_info(png_ptr, info_ptr);
3655 Note that there is one transformation you may need to do before
3656 png_write_info(). In PNG files, the alpha channel in an image is the
3657 level of opacity. If your data is supplied as a level of transparency,
3658 you can invert the alpha channel before you write it, so that 0 is
3659 fully transparent and 255 (in 8-bit or paletted images) or 65535
3660 (in 16-bit images) is fully opaque, with
3662 png_set_invert_alpha(png_ptr);
3664 This must appear before png_write_info() instead of later with the
3665 other transformations because in the case of paletted images the tRNS
3666 chunk data has to be inverted before the tRNS chunk is written. If
3667 your image is not a paletted image, the tRNS data (which in such cases
3668 represents a single color to be rendered as transparent) won't need to
3669 be changed, and you can safely do this transformation after your
3670 png_write_info() call.
3672 If you need to write a private chunk that you want to appear before
3673 the PLTE chunk when PLTE is present, you can write the PNG info in
3674 two steps, and insert code to write your own chunk between them:
3676 png_write_info_before_PLTE(png_ptr, info_ptr);
3677 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3678 png_write_info(png_ptr, info_ptr);
3680 After you've written the file information, you can set up the library
3681 to handle any special transformations of the image data. The various
3682 ways to transform the data will be described in the order that they
3683 should occur. This is important, as some of these change the color
3684 type and/or bit depth of the data, and some others only work on
3685 certain color types and bit depths. Even though each transformation
3686 checks to see if it has data that it can do something with, you should
3687 make sure to only enable a transformation if it will be valid for the
3688 data. For example, don't swap red and blue on grayscale data.
3690 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3691 the library to strip input data that has 4 or 8 bytes per pixel down
3692 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3695 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3697 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3698 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3699 is stored XRGB or RGBX.
3701 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3702 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3703 If the data is supplied at 1 pixel per byte, use this code, which will
3704 correctly pack the pixels into a single byte:
3706 png_set_packing(png_ptr);
3708 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3709 data is of another bit depth, you can write an sBIT chunk into the
3710 file so that decoders can recover the original data if desired.
3712 /* Set the true bit depth of the image data */
3713 if (color_type & PNG_COLOR_MASK_COLOR)
3715 sig_bit.red = true_bit_depth;
3716 sig_bit.green = true_bit_depth;
3717 sig_bit.blue = true_bit_depth;
3722 sig_bit.gray = true_bit_depth;
3725 if (color_type & PNG_COLOR_MASK_ALPHA)
3727 sig_bit.alpha = true_bit_depth;
3730 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3732 If the data is stored in the row buffer in a bit depth other than
3733 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3734 this will scale the values to appear to be the correct bit depth as
3737 png_set_shift(png_ptr, &sig_bit);
3739 PNG files store 16 bit pixels in network byte order (big-endian,
3740 ie. most significant bits first). This code would be used if they are
3741 supplied the other way (little-endian, i.e. least significant bits
3742 first, the way PCs store them):
3745 png_set_swap(png_ptr);
3747 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3748 need to change the order the pixels are packed into bytes, you can use:
3751 png_set_packswap(png_ptr);
3753 PNG files store 3 color pixels in red, green, blue order. This code
3754 would be used if they are supplied as blue, green, red:
3756 png_set_bgr(png_ptr);
3758 PNG files describe monochrome as black being zero and white being
3759 one. This code would be used if the pixels are supplied with this reversed
3760 (black being one and white being zero):
3762 png_set_invert_mono(png_ptr);
3764 Finally, you can write your own transformation function if none of
3765 the existing ones meets your needs. This is done by setting a callback
3768 png_set_write_user_transform_fn(png_ptr,
3769 write_transform_fn);
3771 You must supply the function
3773 void write_transform_fn(png_structp png_ptr, png_row_infop
3774 row_info, png_bytep data)
3776 See pngtest.c for a working example. Your function will be called
3777 before any of the other transformations are processed. If supported
3778 libpng also supplies an information routine that may be called from
3781 png_get_current_row_number(png_ptr);
3782 png_get_current_pass_number(png_ptr);
3784 This returns the current row passed to the transform. With interlaced
3785 images the value returned is the row in the input sub-image image. Use
3786 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
3787 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
3789 The discussion of interlace handling above contains more information on how to
3792 You can also set up a pointer to a user structure for use by your
3795 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3797 The user_channels and user_depth parameters of this function are ignored
3798 when writing; you can set them to zero as shown.
3800 You can retrieve the pointer via the function png_get_user_transform_ptr().
3803 voidp write_user_transform_ptr =
3804 png_get_user_transform_ptr(png_ptr);
3806 It is possible to have libpng flush any pending output, either manually,
3807 or automatically after a certain number of lines have been written. To
3808 flush the output stream a single time call:
3810 png_write_flush(png_ptr);
3812 and to have libpng flush the output stream periodically after a certain
3813 number of scanlines have been written, call:
3815 png_set_flush(png_ptr, nrows);
3817 Note that the distance between rows is from the last time png_write_flush()
3818 was called, or the first row of the image if it has never been called.
3819 So if you write 50 lines, and then png_set_flush 25, it will flush the
3820 output on the next scanline, and every 25 lines thereafter, unless
3821 png_write_flush() is called before 25 more lines have been written.
3822 If nrows is too small (less than about 10 lines for a 640 pixel wide
3823 RGB image) the image compression may decrease noticeably (although this
3824 may be acceptable for real-time applications). Infrequent flushing will
3825 only degrade the compression performance by a few percent over images
3826 that do not use flushing.
3828 .SS Writing the image data
3830 That's it for the transformations. Now you can write the image data.
3831 The simplest way to do this is in one function call. If you have the
3832 whole image in memory, you can just call png_write_image() and libpng
3833 will write the image. You will need to pass in an array of pointers to
3834 each row. This function automatically handles interlacing, so you don't
3835 need to call png_set_interlace_handling() or call this function multiple
3836 times, or any of that other stuff necessary with png_write_rows().
3838 png_write_image(png_ptr, row_pointers);
3840 where row_pointers is:
3842 png_byte *row_pointers[height];
3844 You can point to void or char or whatever you use for pixels.
3846 If you don't want to write the whole image at once, you can
3847 use png_write_rows() instead. If the file is not interlaced,
3850 png_write_rows(png_ptr, row_pointers,
3853 row_pointers is the same as in the png_write_image() call.
3855 If you are just writing one row at a time, you can do this with
3856 a single row_pointer instead of an array of row_pointers:
3858 png_bytep row_pointer = row;
3860 png_write_row(png_ptr, row_pointer);
3862 When the file is interlaced, things can get a good deal more complicated.
3863 The only currently (as of the PNG Specification version 1.2, dated July
3864 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
3865 scheme, that breaks down an image into seven smaller images of varying
3866 size. libpng will build these images for you, or you can do them
3867 yourself. If you want to build them yourself, see the PNG specification
3868 for details of which pixels to write when.
3870 If you don't want libpng to handle the interlacing details, just
3871 use png_set_interlace_handling() and call png_write_rows() the
3872 correct number of times to write all the sub-images
3873 (png_set_interlace_handling() returns the number of sub-images.)
3875 If you want libpng to build the sub-images, call this before you start
3878 number_of_passes = png_set_interlace_handling(png_ptr);
3880 This will return the number of passes needed. Currently, this is seven,
3881 but may change if another interlace type is added.
3883 Then write the complete image number_of_passes times.
3885 png_write_rows(png_ptr, row_pointers, number_of_rows);
3887 Think carefully before you write an interlaced image. Typically code that
3888 reads such images reads all the image data into memory, uncompressed, before
3889 doing any processing. Only code that can display an image on the fly can
3890 take advantage of the interlacing and even then the image has to be exactly
3891 the correct size for the output device, because scaling an image requires
3892 adjacent pixels and these are not available until all the passes have been
3895 If you do write an interlaced image you will hardly ever need to handle
3896 the interlacing yourself. Call png_set_interlace_handling() and use the
3897 approach described above.
3899 The only time it is conceivable that you will really need to write an
3900 interlaced image pass-by-pass is when you have read one pass by pass and
3901 made some pixel-by-pixel transformation to it, as described in the read
3902 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
3903 to determine the size of each sub-image in turn and simply write the rows
3904 you obtained from the read code.
3906 .SS Finishing a sequential write
3908 After you are finished writing the image, you should finish writing
3909 the file. If you are interested in writing comments or time, you should
3910 pass an appropriately filled png_info pointer. If you are not interested,
3913 png_write_end(png_ptr, info_ptr);
3915 When you are done, you can free all memory used by libpng like this:
3917 png_destroy_write_struct(&png_ptr, &info_ptr);
3919 It is also possible to individually free the info_ptr members that
3920 point to libpng-allocated storage with the following function:
3922 png_free_data(png_ptr, info_ptr, mask, seq)
3924 mask - identifies data to be freed, a mask
3925 containing the bitwise OR of one or
3927 PNG_FREE_PLTE, PNG_FREE_TRNS,
3928 PNG_FREE_HIST, PNG_FREE_ICCP,
3929 PNG_FREE_PCAL, PNG_FREE_ROWS,
3930 PNG_FREE_SCAL, PNG_FREE_SPLT,
3931 PNG_FREE_TEXT, PNG_FREE_UNKN,
3932 or simply PNG_FREE_ALL
3934 seq - sequence number of item to be freed
3937 This function may be safely called when the relevant storage has
3938 already been freed, or has not yet been allocated, or was allocated
3939 by the user and not by libpng, and will in those cases do nothing.
3940 The "seq" parameter is ignored if only one item of the selected data
3941 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3942 are allowed for the data type identified in the mask, such as text or
3943 sPLT, only the n'th item in the structure is freed, where n is "seq".
3945 If you allocated data such as a palette that you passed in to libpng
3946 with png_set_*, you must not free it until just before the call to
3947 png_destroy_write_struct().
3949 The default behavior is only to free data that was allocated internally
3950 by libpng. This can be changed, so that libpng will not free the data,
3951 or so that it will free data that was allocated by the user with png_malloc()
3952 or png_zalloc() and passed in via a png_set_*() function, with
3954 png_data_freer(png_ptr, info_ptr, freer, mask)
3957 PNG_DESTROY_WILL_FREE_DATA
3958 PNG_SET_WILL_FREE_DATA
3959 PNG_USER_WILL_FREE_DATA
3961 mask - which data elements are affected
3962 same choices as in png_free_data()
3964 For example, to transfer responsibility for some data from a read structure
3965 to a write structure, you could use
3967 png_data_freer(read_ptr, read_info_ptr,
3968 PNG_USER_WILL_FREE_DATA,
3969 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3971 png_data_freer(write_ptr, write_info_ptr,
3972 PNG_DESTROY_WILL_FREE_DATA,
3973 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3975 thereby briefly reassigning responsibility for freeing to the user but
3976 immediately afterwards reassigning it once more to the write_destroy
3977 function. Having done this, it would then be safe to destroy the read
3978 structure and continue to use the PLTE, tRNS, and hIST data in the write
3981 This function only affects data that has already been allocated.
3982 You can call this function before calling after the png_set_*() functions
3983 to control whether the user or png_destroy_*() is supposed to free the data.
3984 When the user assumes responsibility for libpng-allocated data, the
3985 application must use
3986 png_free() to free it, and when the user transfers responsibility to libpng
3987 for data that the user has allocated, the user must have used png_malloc()
3988 or png_zalloc() to allocate it.
3990 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3991 separately, do not transfer responsibility for freeing text_ptr to libpng,
3992 because when libpng fills a png_text structure it combines these members with
3993 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3994 if you transfer responsibility for free'ing text_ptr from libpng to your
3995 application, your application must not separately free those members.
3996 For a more compact example of writing a PNG image, see the file example.c.
3998 .SH V. Modifying/Customizing libpng:
4000 There are two issues here. The first is changing how libpng does
4001 standard things like memory allocation, input/output, and error handling.
4002 The second deals with more complicated things like adding new chunks,
4003 adding new transformations, and generally changing how libpng works.
4004 Both of those are compile-time issues; that is, they are generally
4005 determined at the time the code is written, and there is rarely a need
4006 to provide the user with a means of changing them.
4008 Memory allocation, input/output, and error handling
4010 All of the memory allocation, input/output, and error handling in libpng
4011 goes through callbacks that are user-settable. The default routines are
4012 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4013 these functions, call the appropriate png_set_*_fn() function.
4015 Memory allocation is done through the functions png_malloc(), png_calloc(),
4016 and png_free(). These currently just call the standard C functions.
4017 png_calloc() calls png_malloc() and then clears the newly
4018 allocated memory to zero. There is limited support for certain systems
4019 with segmented memory architectures and the types of pointers declared by
4020 png.h match this; you will have to use appropriate pointers in your
4021 application. Since it is
4022 unlikely that the method of handling memory allocation on a platform
4023 will change between applications, these functions must be modified in
4024 the library at compile time. If you prefer to use a different method
4025 of allocating and freeing data, you can use png_create_read_struct_2() or
4026 png_create_write_struct_2() to register your own functions as described
4027 above. These functions also provide a void pointer that can be retrieved
4030 mem_ptr=png_get_mem_ptr(png_ptr);
4032 Your replacement memory functions must have prototypes as follows:
4034 png_voidp malloc_fn(png_structp png_ptr,
4035 png_alloc_size_t size);
4037 void free_fn(png_structp png_ptr, png_voidp ptr);
4039 Your malloc_fn() must return NULL in case of failure. The png_malloc()
4040 function will normally call png_error() if it receives a NULL from the
4041 system memory allocator or from your replacement malloc_fn().
4043 Your free_fn() will never be called with a NULL ptr, since libpng's
4044 png_free() checks for NULL before calling free_fn().
4046 Input/Output in libpng is done through png_read() and png_write(),
4047 which currently just call fread() and fwrite(). The FILE * is stored in
4048 png_struct and is initialized via png_init_io(). If you wish to change
4049 the method of I/O, the library supplies callbacks that you can set
4050 through the function png_set_read_fn() and png_set_write_fn() at run
4051 time, instead of calling the png_init_io() function. These functions
4052 also provide a void pointer that can be retrieved via the function
4053 png_get_io_ptr(). For example:
4055 png_set_read_fn(png_structp read_ptr,
4056 voidp read_io_ptr, png_rw_ptr read_data_fn)
4058 png_set_write_fn(png_structp write_ptr,
4059 voidp write_io_ptr, png_rw_ptr write_data_fn,
4060 png_flush_ptr output_flush_fn);
4062 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4063 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4065 The replacement I/O functions must have prototypes as follows:
4067 void user_read_data(png_structp png_ptr,
4068 png_bytep data, png_size_t length);
4070 void user_write_data(png_structp png_ptr,
4071 png_bytep data, png_size_t length);
4073 void user_flush_data(png_structp png_ptr);
4075 The user_read_data() function is responsible for detecting and
4076 handling end-of-data errors.
4078 Supplying NULL for the read, write, or flush functions sets them back
4079 to using the default C stream functions, which expect the io_ptr to
4080 point to a standard *FILE structure. It is probably a mistake
4081 to use NULL for one of write_data_fn and output_flush_fn but not both
4082 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4083 It is an error to read from a write stream, and vice versa.
4085 Error handling in libpng is done through png_error() and png_warning().
4086 Errors handled through png_error() are fatal, meaning that png_error()
4087 should never return to its caller. Currently, this is handled via
4088 setjmp() and longjmp() (unless you have compiled libpng with
4089 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4090 but you could change this to do things like exit() if you should wish,
4091 as long as your function does not return.
4093 On non-fatal errors, png_warning() is called
4094 to print a warning message, and then control returns to the calling code.
4095 By default png_error() and png_warning() print a message on stderr via
4096 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4097 (because you don't want the messages) or PNG_NO_STDIO defined (because
4098 fprintf() isn't available). If you wish to change the behavior of the error
4099 functions, you will need to set up your own message callbacks. These
4100 functions are normally supplied at the time that the png_struct is created.
4101 It is also possible to redirect errors and warnings to your own replacement
4102 functions after png_create_*_struct() has been called by calling:
4104 png_set_error_fn(png_structp png_ptr,
4105 png_voidp error_ptr, png_error_ptr error_fn,
4106 png_error_ptr warning_fn);
4108 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4110 If NULL is supplied for either error_fn or warning_fn, then the libpng
4111 default function will be used, calling fprintf() and/or longjmp() if a
4112 problem is encountered. The replacement error functions should have
4113 parameters as follows:
4115 void user_error_fn(png_structp png_ptr,
4116 png_const_charp error_msg);
4118 void user_warning_fn(png_structp png_ptr,
4119 png_const_charp warning_msg);
4121 The motivation behind using setjmp() and longjmp() is the C++ throw and
4122 catch exception handling methods. This makes the code much easier to write,
4123 as there is no need to check every return code of every function call.
4124 However, there are some uncertainties about the status of local variables
4125 after a longjmp, so the user may want to be careful about doing anything
4126 after setjmp returns non-zero besides returning itself. Consult your
4127 compiler documentation for more details. For an alternative approach, you
4128 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
4132 If you need to read or write custom chunks, you may need to get deeper
4133 into the libpng code. The library now has mechanisms for storing
4134 and writing chunks of unknown type; you can even declare callbacks
4135 for custom chunks. However, this may not be good enough if the
4136 library code itself needs to know about interactions between your
4137 chunk and existing `intrinsic' chunks.
4139 If you need to write a new intrinsic chunk, first read the PNG
4140 specification. Acquire a first level of understanding of how it works.
4141 Pay particular attention to the sections that describe chunk names,
4142 and look at how other chunks were designed, so you can do things
4143 similarly. Second, check out the sections of libpng that read and
4144 write chunks. Try to find a chunk that is similar to yours and use
4145 it as a template. More details can be found in the comments inside
4146 the code. It is best to handle unknown chunks in a generic method,
4147 via callback functions, instead of by modifying libpng functions.
4149 If you wish to write your own transformation for the data, look through
4150 the part of the code that does the transformations, and check out some of
4151 the simpler ones to get an idea of how they work. Try to find a similar
4152 transformation to the one you want to add and copy off of it. More details
4153 can be found in the comments inside the code itself.
4155 .SS Configuring for 16 bit platforms
4157 You will want to look into zconf.h to tell zlib (and thus libpng) that
4158 it cannot allocate more then 64K at a time. Even if you can, the memory
4159 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4161 .SS Configuring for DOS
4163 For DOS users who only have access to the lower 640K, you will
4164 have to limit zlib's memory usage via a png_set_compression_mem_level()
4165 call. See zlib.h or zconf.h in the zlib library for more information.
4167 .SS Configuring for Medium Model
4169 Libpng's support for medium model has been tested on most of the popular
4170 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4171 defined, and FAR gets defined to far in pngconf.h, and you should be
4172 all set. Everything in the library (except for zlib's structure) is
4173 expecting far data. You must use the typedefs with the p or pp on
4174 the end for pointers (or at least look at them and be careful). Make
4175 note that the rows of data are defined as png_bytepp, which is an
4176 unsigned char far * far *.
4178 .SS Configuring for gui/windowing platforms:
4180 You will need to write new error and warning functions that use the GUI
4181 interface, as described previously, and set them to be the error and
4182 warning functions at the time that png_create_*_struct() is called,
4183 in order to have them available during the structure initialization.
4184 They can be changed later via png_set_error_fn(). On some compilers,
4185 you may also have to change the memory allocators (png_malloc, etc.).
4187 .SS Configuring for compiler xxx:
4189 All includes for libpng are in pngconf.h. If you need to add, change
4190 or delete an include, this is the place to do it.
4191 The includes that are not needed outside libpng are placed in pngpriv.h,
4192 which is only used by the routines inside libpng itself.
4193 The files in libpng proper only include pngpriv.h and png.h, which
4194 in turn includes pngconf.h.
4196 .SS Configuring zlib:
4198 There are special functions to configure the compression. Perhaps the
4199 most useful one changes the compression level, which currently uses
4200 input compression values in the range 0 - 9. The library normally
4201 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4202 have shown that for a large majority of images, compression values in
4203 the range 3-6 compress nearly as well as higher levels, and do so much
4204 faster. For online applications it may be desirable to have maximum speed
4205 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4206 specify no compression (Z_NO_COMPRESSION = 0), but this would create
4207 files larger than just storing the raw bitmap. You can specify the
4208 compression level by calling:
4211 png_set_compression_level(png_ptr, level);
4213 Another useful one is to reduce the memory level used by the library.
4214 The memory level defaults to 8, but it can be lowered if you are
4215 short on memory (running DOS, for example, where you only have 640K).
4216 Note that the memory level does have an effect on compression; among
4217 other things, lower levels will result in sections of incompressible
4218 data being emitted in smaller stored blocks, with a correspondingly
4219 larger relative overhead of up to 15% in the worst case.
4222 png_set_compression_mem_level(png_ptr, level);
4224 The other functions are for configuring zlib. They are not recommended
4225 for normal use and may result in writing an invalid PNG file. See
4226 zlib.h for more information on what these mean.
4229 png_set_compression_strategy(png_ptr,
4232 png_set_compression_window_bits(png_ptr,
4235 png_set_compression_method(png_ptr, method);
4236 png_set_compression_buffer_size(png_ptr, size);
4238 .SS Controlling row filtering
4240 If you want to control whether libpng uses filtering or not, which
4241 filters are used, and how it goes about picking row filters, you
4242 can call one of these functions. The selection and configuration
4243 of row filters can have a significant impact on the size and
4244 encoding speed and a somewhat lesser impact on the decoding speed
4245 of an image. Filtering is enabled by default for RGB and grayscale
4246 images (with and without alpha), but not for paletted images nor
4247 for any images with bit depths less than 8 bits/pixel.
4249 The 'method' parameter sets the main filtering method, which is
4250 currently only '0' in the PNG 1.2 specification. The 'filters'
4251 parameter sets which filter(s), if any, should be used for each
4252 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4253 to turn filtering on and off, respectively.
4255 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4256 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4257 ORed together with '|' to specify one or more filters to use.
4258 These filters are described in more detail in the PNG specification.
4259 If you intend to change the filter type during the course of writing
4260 the image, you should start with flags set for all of the filters
4261 you intend to use so that libpng can initialize its internal
4262 structures appropriately for all of the filter types. (Note that this
4263 means the first row must always be adaptively filtered, because libpng
4264 currently does not allocate the filter buffers until png_write_row()
4265 is called for the first time.)
4267 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4268 PNG_FILTER_UP | PNG_FILTER_AVG |
4269 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4271 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4273 The second parameter can also be
4274 PNG_INTRAPIXEL_DIFFERENCING if you are
4275 writing a PNG to be embedded in a MNG
4276 datastream. This parameter must be the
4277 same as the value of filter_method used
4280 It is also possible to influence how libpng chooses from among the
4281 available filters. This is done in one or both of two ways - by
4282 telling it how important it is to keep the same filter for successive
4283 rows, and by telling it the relative computational costs of the filters.
4285 double weights[3] = {1.5, 1.3, 1.1},
4286 costs[PNG_FILTER_VALUE_LAST] =
4287 {1.0, 1.3, 1.3, 1.5, 1.7};
4289 png_set_filter_heuristics(png_ptr,
4290 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4293 The weights are multiplying factors that indicate to libpng that the
4294 row filter should be the same for successive rows unless another row filter
4295 is that many times better than the previous filter. In the above example,
4296 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4297 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
4298 and still be chosen, while the NONE filter could have a sum 1.1 times
4299 higher than other filters and still be chosen. Unspecified weights are
4300 taken to be 1.0, and the specified weights should probably be declining
4301 like those above in order to emphasize recent filters over older filters.
4303 The filter costs specify for each filter type a relative decoding cost
4304 to be considered when selecting row filters. This means that filters
4305 with higher costs are less likely to be chosen over filters with lower
4306 costs, unless their "sum of absolute differences" is that much smaller.
4307 The costs do not necessarily reflect the exact computational speeds of
4308 the various filters, since this would unduly influence the final image
4311 Note that the numbers above were invented purely for this example and
4312 are given only to help explain the function usage. Little testing has
4313 been done to find optimum values for either the costs or the weights.
4315 .SS Removing unwanted object code
4317 There are a bunch of #define's in pngconf.h that control what parts of
4318 libpng are compiled. All the defines end in _SUPPORTED. If you are
4319 never going to use a capability, you can change the #define to #undef
4320 before recompiling libpng and save yourself code and data space, or
4321 you can turn off individual capabilities with defines that begin with
4324 In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4326 You can also turn all of the transforms and ancillary chunk capabilities
4327 off en masse with compiler directives that define
4328 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4330 along with directives to turn on any of the capabilities that you do
4331 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4332 transformations but still leave the library fully capable of reading
4333 and writing PNG files with all known public chunks. Use of the
4334 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4335 that is incapable of reading or writing ancillary chunks. If you are
4336 not using the progressive reading capability, you can turn that off
4337 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4338 capability, which you'll still have).
4340 All the reading and writing specific code are in separate files, so the
4341 linker should only grab the files it needs. However, if you want to
4342 make sure, or if you are building a stand alone library, all the
4343 reading files start with pngr and all the writing files start with
4344 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
4345 are used for both reading and writing, and always need to be included.
4346 The progressive reader is in pngpread.c
4348 If you are creating or distributing a dynamically linked library (a .so
4349 or DLL file), you should not remove or disable any parts of the library,
4350 as this will cause applications linked with different versions of the
4351 library to fail if they call functions not available in your library.
4352 The size of the library itself should not be an issue, because only
4353 those sections that are actually used will be loaded into memory.
4355 .SS Requesting debug printout
4357 The macro definition PNG_DEBUG can be used to request debugging
4358 printout. Set it to an integer value in the range 0 to 3. Higher
4359 numbers result in increasing amounts of debugging information. The
4360 information is printed to the "stderr" file, unless another file
4361 name is specified in the PNG_DEBUG_FILE macro definition.
4363 When PNG_DEBUG > 0, the following functions (macros) become available:
4365 png_debug(level, message)
4366 png_debug1(level, message, p1)
4367 png_debug2(level, message, p1, p2)
4369 in which "level" is compared to PNG_DEBUG to decide whether to print
4370 the message, "message" is the formatted string to be printed,
4371 and p1 and p2 are parameters that are to be embedded in the string
4372 according to printf-style formatting directives. For example,
4374 png_debug1(2, "foo=%d\n", foo);
4379 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4381 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4382 can still use PNG_DEBUG to control your own debugging:
4388 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4389 having level = 0 will be printed. There aren't any such statements in
4390 this version of libpng, but if you insert some they will be printed.
4394 The MNG specification (available at http://www.libpng.org/pub/mng) allows
4395 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4396 Libpng can support some of these extensions. To enable them, use the
4397 png_permit_mng_features() function:
4399 feature_set = png_permit_mng_features(png_ptr, mask)
4401 mask is a png_uint_32 containing the bitwise OR of the
4402 features you want to enable. These include
4403 PNG_FLAG_MNG_EMPTY_PLTE
4404 PNG_FLAG_MNG_FILTER_64
4405 PNG_ALL_MNG_FEATURES
4407 feature_set is a png_uint_32 that is the bitwise AND of
4408 your mask with the set of MNG features that is
4409 supported by the version of libpng that you are using.
4411 It is an error to use this function when reading or writing a standalone
4412 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4413 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4414 and the MHDR and MEND chunks. Libpng does not provide support for these
4415 or any other MNG chunks; your application must provide its own support for
4416 them. You may wish to consider using libmng (available at
4417 http://www.libmng.com) instead.
4419 .SH VII. Changes to Libpng from version 0.88
4421 It should be noted that versions of libpng later than 0.96 are not
4422 distributed by the original libpng author, Guy Schalnat, nor by
4423 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4424 distributed versions 0.89 through 0.96, but rather by another member
4425 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4426 still alive and well, but they have moved on to other things.
4428 The old libpng functions png_read_init(), png_write_init(),
4429 png_info_init(), png_read_destroy(), and png_write_destroy() have been
4430 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4431 functions will be removed from libpng version 1.4.0.
4433 The preferred method of creating and initializing the libpng structures is
4434 via the png_create_read_struct(), png_create_write_struct(), and
4435 png_create_info_struct() because they isolate the size of the structures
4436 from the application, allow version error checking, and also allow the
4437 use of custom error handling routines during the initialization, which
4438 the old functions do not. The functions png_read_destroy() and
4439 png_write_destroy() do not actually free the memory that libpng
4440 allocated for these structs, but just reset the data structures, so they
4441 can be used instead of png_destroy_read_struct() and
4442 png_destroy_write_struct() if you feel there is too much system overhead
4443 allocating and freeing the png_struct for each image read.
4445 Setting the error callbacks via png_set_message_fn() before
4446 png_read_init() as was suggested in libpng-0.88 is no longer supported
4447 because this caused applications that do not use custom error functions
4448 to fail if the png_ptr was not initialized to zero. It is still possible
4449 to set the error callbacks AFTER png_read_init(), or to change them with
4450 png_set_error_fn(), which is essentially the same function, but with a new
4451 name to force compilation errors with applications that try to use the old
4454 Starting with version 1.0.7, you can find out which version of the library
4455 you are using at run-time:
4457 png_uint_32 libpng_vn = png_access_version_number();
4459 The number libpng_vn is constructed from the major version, minor
4460 version with leading zero, and release number with leading zero,
4461 (e.g., libpng_vn for version 1.0.7 is 10007).
4463 You can also check which version of png.h you used when compiling your
4466 png_uint_32 application_vn = PNG_LIBPNG_VER;
4468 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
4470 Support for user memory management was enabled by default. To
4471 accomplish this, the functions png_create_read_struct_2(),
4472 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4473 png_malloc_default(), and png_free_default() were added.
4475 Support for the iTXt chunk has been enabled by default as of
4478 Support for certain MNG features was enabled.
4480 Support for numbered error messages was added. However, we never got
4481 around to actually numbering the error messages. The function
4482 png_set_strip_error_numbers() was added (Note: the prototype for this
4483 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4484 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4486 The png_malloc_warn() function was added at libpng-1.2.3. This issues
4487 a png_warning and returns NULL instead of aborting when it fails to
4488 acquire the requested memory allocation.
4490 Support for setting user limits on image width and height was enabled
4491 by default. The functions png_set_user_limits(), png_get_user_width_max(),
4492 and png_get_user_height_max() were added at libpng-1.2.6.
4494 The png_set_add_alpha() function was added at libpng-1.2.7.
4496 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4497 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4498 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4501 A number of macro definitions in support of runtime selection of
4502 assembler code features (especially Intel MMX code support) were
4503 added at libpng-1.2.0:
4505 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4506 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4507 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4508 PNG_ASM_FLAG_MMX_READ_INTERLACE
4509 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4510 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4511 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4512 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4513 PNG_ASM_FLAGS_INITIALIZED
4519 We added the following functions in support of runtime
4520 selection of assembler code features:
4522 png_get_mmx_flagmask()
4523 png_set_mmx_thresholds()
4525 png_get_mmx_bitdepth_threshold()
4526 png_get_mmx_rowbytes_threshold()
4529 We replaced all of these functions with simple stubs in libpng-1.2.20,
4530 when the Intel assembler code was removed due to a licensing issue.
4532 These macros are deprecated:
4534 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4535 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4536 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4537 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4538 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4539 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4541 They have been replaced, respectively, by:
4543 PNG_NO_READ_TRANSFORMS
4544 PNG_NO_PROGRESSIVE_READ
4545 PNG_NO_SEQUENTIAL_READ
4546 PNG_NO_WRITE_TRANSFORMS
4547 PNG_NO_READ_ANCILLARY_CHUNKS
4548 PNG_NO_WRITE_ANCILLARY_CHUNKS
4550 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4551 deprecated since libpng-1.0.16 and libpng-1.2.6.
4554 png_check_sig(sig, num)
4556 !png_sig_cmp(sig, 0, num)
4557 It has been deprecated since libpng-0.90.
4560 png_set_gray_1_2_4_to_8()
4561 which also expands tRNS to alpha was replaced with
4562 png_set_expand_gray_1_2_4_to_8()
4563 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
4565 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
4567 Private libpng prototypes and macro definitions were moved from
4568 png.h and pngconf.h into a new pngpriv.h header file.
4570 Functions png_set_benign_errors(), png_benign_error(), and
4571 png_chunk_benign_error() were added.
4573 Support for setting the maximum amount of memory that the application
4574 will allocate for reading chunks was added, as a security measure.
4575 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
4576 were added to the library.
4578 We implemented support for I/O states by adding png_ptr member io_state
4579 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
4581 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
4584 Checking for and reporting of errors in the IHDR chunk is more thorough.
4586 Support for global arrays was removed, to improve thread safety.
4588 Some obsolete/deprecated macros and functions have been removed.
4590 Typecasted NULL definitions such as
4591 #define png_voidp_NULL (png_voidp)NULL
4592 were eliminated. If you used these in your application, just use
4595 The png_struct and info_struct members "trans" and "trans_values" were
4596 changed to "trans_alpha" and "trans_color", respectively.
4598 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
4601 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
4603 The PNG_LEGACY_SUPPORTED macro was eliminated.
4605 Many WIN32_WCE #ifdefs were removed.
4607 The functions png_read_init(info_ptr), png_write_init(info_ptr),
4608 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
4609 have been removed. They have been deprecated since libpng-0.95.
4611 The png_permit_empty_plte() was removed. It has been deprecated
4612 since libpng-1.0.9. Use png_permit_mng_features() instead.
4614 We removed the obsolete stub functions png_get_mmx_flagmask(),
4615 png_set_mmx_thresholds(), png_get_asm_flags(),
4616 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
4617 png_set_asm_flags(), and png_mmx_supported()
4619 We removed the obsolete png_check_sig(), png_memcpy_check(), and
4620 png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
4621 and memset(), respectively.
4623 The function png_set_gray_1_2_4_to_8() was removed. It has been
4624 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
4625 png_set_expand_gray_1_2_4_to_8() because the former function also
4626 expanded any tRNS chunk to an alpha channel.
4628 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
4629 were added and are used by default instead of the corresponding
4630 functions. Unfortunately,
4631 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4632 function) incorrectly returned a value of type png_uint_32.
4634 We changed the prototype for png_malloc() from
4635 png_malloc(png_structp png_ptr, png_uint_32 size)
4637 png_malloc(png_structp png_ptr, png_alloc_size_t size)
4639 This also applies to the prototype for the user replacement malloc_fn().
4641 The png_calloc() function was added and is used in place of
4642 of "png_malloc(); memset();" except in the case in png_read_png()
4643 where the array consists of pointers; in this case a "for" loop is used
4644 after the png_malloc() to set the pointers to NULL, to give robust.
4645 behavior in case the application runs out of memory part-way through
4648 We changed the prototypes of png_get_compression_buffer_size() and
4649 png_set_compression_buffer_size() to work with png_size_t instead of
4652 Support for numbered error messages was removed by default, since we
4653 never got around to actually numbering the error messages. The function
4654 png_set_strip_error_numbers() was removed from the library by default.
4656 The png_zalloc() and png_zfree() functions are no longer exported.
4657 The png_zalloc() function no longer zeroes out the memory that it
4660 Support for dithering was disabled by default in libpng-1.4.0, because
4661 been well tested and doesn't actually "dither". The code was not
4662 removed, however, and could be enabled by building libpng with
4663 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
4664 was reenabled, but the function was renamed png_set_quantize() to
4665 reflect more accurately what it actually does. At the same time,
4666 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
4667 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
4668 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
4670 We removed the trailing '.' from the warning and error messages.
4672 .SH X. Changes to Libpng from version 1.4.x to 1.5.x
4674 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4675 function) incorrectly returned a value of type png_uint_32.
4677 A. Changes that affect users of libpng
4679 There are no substantial API changes between the non-deprecated parts of
4680 the 1.4.5 API and the 1.5.0 API, however the ability to directly access
4681 the main libpng control structures, png_struct and png_info, deprecated
4682 in earlier versions of libpng, has been completely removed from
4685 We no longer include zlib.h in png.h. Applications that need access
4686 to information in zlib.h will need to add the '#include "zlib.h"'
4687 directive. It does not matter whether it is placed prior to or after
4688 the '"#include png.h"' directive.
4690 We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),
4691 png_memcmp(), png_sprintf, and png_memcpy() macros into a private
4692 header file (pngpriv.h) that is not accessible to applications.
4694 In png_get_iCCP, the type of "profile" was changed from png_charpp
4695 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
4697 There are changes of form in png.h, including new and changed macros to
4699 parts of the API. Some API functions with arguments that are pointers to
4700 data not modified within the function have been corrected to declare
4701 these arguments with PNG_CONST.
4703 Much of the internal use of C macros to control the library build has also
4704 changed and some of this is visible in the exported header files, in
4705 particular the use of macros to control data and API elements visible
4706 during application compilation may require significant revision to
4707 application code. (It is extremely rare for an application to do this.)
4709 Any program that compiled against libpng 1.4 and did not use deprecated
4710 features or access internal library structures should compile and work
4711 against libpng 1.5, except for the change in the prototype for
4712 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
4714 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
4715 interlaced images. The macros return the number of rows and columns in
4716 each pass and information that can be used to de-interlace and (if
4717 absolutely necessary) interlace an image.
4719 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
4720 the application-provided png_longjmp_ptr on the internal, but application
4721 initialized, jmpbuf. It is provided as a convenience to avoid the need
4722 to use the png_jmpbuf macro, which had the unnecessary side effect of
4723 resetting the internal png_longjmp_ptr value.
4725 libpng 1.5.0 includes a complete fixed point API. By default this is
4726 present along with the corresponding floating point API. In general the
4727 fixed point API is faster and smaller than the floating point one because
4728 the PNG file format used fixed point, not floating point. This applies
4729 even if the library uses floating point in internal calculations. A new
4730 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
4731 uses floating point arithmetic (the default) or fixed point arithmetic
4732 internally for performance critical calculations such as gamma correction.
4733 In some cases, the gamma calculations may produce slightly different
4734 results. This has changed the results in png_rgb_to_gray and in alpha
4735 composition (png_set_background for example). This applies even if the
4736 original image was already linear (gamma == 1.0) and, therefore, it is
4737 not necessary to linearize the image. This is because libpng has *not*
4738 been changed to optimize that case correctly, yet.
4740 Fixed point support for the sCAL chunk comes with an important caveat;
4741 the sCAL specification uses a decimal encoding of floating point values
4742 and the accuracy of PNG fixed point values is insufficient for
4743 representation of these values. Consequently a "string" API
4744 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
4745 arbitrary sCAL chunks in the absence of either the floating point API or
4746 internal floating point calculations.
4748 Applications no longer need to include the optional distribution header
4749 file pngusr.h or define the corresponding macros during application
4750 build in order to see the correct variant of the libpng API. From 1.5.0
4751 application code can check for the corresponding _SUPPORTED macro:
4753 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
4754 /* code that uses the inch conversion APIs. */
4757 This macro will only be defined if the inch conversion functions have been
4758 compiled into libpng. The full set of macros, and whether or not support
4759 has been compiled in, are available in the header file pnglibconf.h.
4760 This header file is specific to the libpng build. Notice that prior to
4761 1.5.0 the _SUPPORTED macros would always have the default definition unless
4762 reset by pngusr.h or by explicit settings on the compiler command line.
4763 These settings may produce compiler warnings or errors in 1.5.0 because
4764 of macro redefinition.
4766 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
4767 function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
4768 is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
4771 Applications can now choose whether to use these macros or to call the
4772 corresponding function by defining PNG_USE_READ_MACROS or
4773 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
4774 only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
4775 will lead to a link failure.
4777 B. Changes to the build and configuration of libpng
4779 Details of internal changes to the library code can be found in the CHANGES
4780 file. These will be of no concern to the vast majority of library users or
4781 builders, however the few who configure libpng to a non-default feature
4782 set may need to change how this is done.
4784 There should be no need for library builders to alter build scripts if
4785 these use the distributed build support - configure or the makefiles -
4786 however users of the makefiles may care to update their build scripts
4787 to build pnglibconf.h where the corresponding makefile does not do so.
4789 Building libpng with a non-default configuration has changed completely.
4790 The old method using pngusr.h should still work correctly even though the
4791 way pngusr.h is used in the build has been changed, however library
4792 builders will probably want to examine the changes to take advantage of
4793 new capabilities and to simplify their build system.
4795 B.1 Specific changes to library configuration capabilities
4797 The library now supports a complete fixed point implementation and can
4798 thus be used on systems which have no floating point support or very
4799 limited or slow support. Previously gamma correction, an essential part
4800 of complete PNG support, required reasonably fast floating point.
4802 As part of this the choice of internal implementation has been made
4803 independent of the choice of fixed versus floating point APIs and all the
4804 missing fixed point APIs have been implemented.
4806 The exact mechanism used to control attributes of API functions has
4807 changed. A single set of operating system independent macro definitions
4808 is used and operating system specific directives are defined in
4811 As part of this the mechanism used to choose procedure call standards on
4812 those systems that allow a choice has been changed. At present this only
4813 affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
4814 running on Intel processors. As before PNGAPI is defined where required
4815 to control the exported API functions; however, two new macros, PNGCBAPI
4816 and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
4817 (PNGCAPI) for functions that must match a C library prototype (currently
4818 only png_longjmp_ptr, which must match the C longjmp function.) The new
4819 approach is documented in pngconf.h
4821 Despite these changes libpng 1.5.0 only supports the native C function
4822 calling standard on those platforms tested so far (__cdecl on Microsoft
4823 Windows). This is because the support requirements for alternative
4824 calling conventions seem to no longer exist. Developers who find it
4825 necessary to set PNG_API_RULE to 1 should advise the mailing list
4826 (png-mng-implement) of this and library builders who use Openwatcom and
4827 therefore set PNG_API_RULE to 2 should also contact the mailing list.
4829 A new test program, pngvalid, is provided in addition to pngtest.
4830 pngvalid validates the arithmetic accuracy of the gamma correction
4831 calculations and includes a number of validations of the file format.
4832 A subset of the full range of tests is run when "make check" is done
4833 (in the 'configure' build.) pngvalid also allows total allocated memory
4834 usage to be evaluated and performs additional memory overwrite validation.
4836 Many changes to individual feature macros have been made. The following
4837 are the changes most likely to be noticed by library builders who
4840 1) All feature macros now have consistent naming:
4842 #define PNG_NO_feature turns the feature off
4843 #define PNG_feature_SUPPORTED turns the feature on
4845 pnglibconf.h contains one line for each feature macro which is either:
4847 #define PNG_feature_SUPPORTED
4849 if the feature is supported or:
4851 /*#undef PNG_feature_SUPPORTED*/
4853 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
4854 It does not, and should not, check for the 'NO' macro which will not
4855 normally be defined even if the feature is not supported.
4857 Compatibility with the old names is provided as follows:
4859 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
4861 And the following definitions disable the corresponding feature:
4863 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
4864 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
4865 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
4866 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
4867 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
4868 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
4870 Library builders should remove use of the above, inconsistent, names.
4872 2) Warning and error message formatting was previously conditional on
4873 the STDIO feature. The library has been changed to use the
4874 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
4875 the library no longer uses the printf(3) functions, even though the
4876 default read/write implementations use (FILE) style stdio.h functions.
4878 3) Three feature macros now control the fixed/floating point decisions:
4880 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
4882 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
4883 practice these are normally required internally anyway (because the PNG
4884 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
4885 merely stops the function from being exported.
4887 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
4888 point implementation or the fixed point one. Typically the fixed point
4889 implementation is larger and slower than the floating point implementation
4890 on a system that supports floating point, however it may be faster on a
4891 system which lacks floating point hardware and therefore uses a software
4894 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
4895 functions to read and write ints to be disabled independently of
4896 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
4897 even though the default is to use the macros - this allows applications
4898 to choose at app buildtime whether or not to use macros (previously
4899 impossible because the functions weren't in the default build.)
4901 B.2 Changes to the configuration mechanism
4903 Prior to libpng-1.5.0 library builders who needed to configure libpng
4904 had either to modify the exported pngconf.h header file to add system
4905 specific configuration or had to write feature selection macros into
4906 pngusr.h and cause this to be included into pngconf.h by defining
4907 PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
4908 application built without PNG_USER_CONFIG defined would see the
4909 unmodified, default, libpng API and thus would probably fail to link.
4911 These mechanisms still work in the configure build and in any makefile
4912 build that builds pnglibconf.h although the feature selection macros
4913 have changed somewhat as described above. In 1.5.0, however, pngusr.h is
4914 processed only once, when the exported header file pnglibconf.h is built.
4915 pngconf.h no longer includes pngusr.h, therefore it is ignored after the
4916 build of pnglibconf.h and it is never included in an application build.
4918 The rarely used alternative of adding a list of feature macros to the
4919 CFLAGS setting in the build also still works, however the macros will be
4920 copied to pnglibconf.h and this may produce macro redefinition warnings
4921 when the individual C files are compiled.
4923 All configuration now only works if pnglibconf.h is built from
4924 scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
4925 (the original author of awk) maintains C source code of that awk and this
4926 and all known later implementations (often called by subtly different
4927 names - nawk and gawk for example) are adequate to build pnglibconf.h.
4928 The Sun Microsystems (now Oracle) program 'awk' is an earlier version
4929 and does not work, this may also apply to other systems that have a
4930 functioning awk called 'nawk'.
4932 Configuration options are now documented in scripts/pnglibconf.dfa. This
4933 file also includes dependency information that ensures a configuration is
4934 consistent; that is, if a feature is switched off dependent features are
4935 also removed. As a recommended alternative to using feature macros in
4936 pngusr.h a system builder may also define equivalent options in pngusr.dfa
4937 (or, indeed, any file) and add that to the configuration by setting
4938 DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
4939 how to do this, and a case where pngusr.h is still required.
4941 .SH XI. Detecting libpng
4943 The png_get_io_ptr() function has been present since libpng-0.88, has never
4944 changed, and is unaffected by conditional compilation macros. It is the
4945 best choice for use in configure scripts for detecting the presence of any
4946 libpng version since 0.88. In an autoconf "configure.in" you could use
4948 AC_CHECK_LIB(png, png_get_io_ptr, ...
4950 .SH XII. Source code repository
4952 Since about February 2009, version 1.2.34, libpng has been under "git" source
4953 control. The git repository was built from old libpng-x.y.z.tar.gz files
4954 going back to version 0.70. You can access the git repository (read only)
4957 git://libpng.git.sourceforge.net/gitroot/libpng
4959 or you can browse it via "gitweb" at
4961 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
4963 Patches can be sent to glennrp at users.sourceforge.net or to
4964 png-mng-implement at lists.sourceforge.net or you can upload them to
4965 the libpng bug tracker at
4967 http://libpng.sourceforge.net
4969 We also accept patches built from the tar or zip distributions, and
4970 simple verbal discriptions of bug fixes, reported either to the
4971 SourceForge bug tracker or to the png-mng-implement at lists.sf.net
4974 .SH XIII. Coding style
4976 Our coding style is similar to the "Allman" style, with curly
4977 braces on separate lines:
4984 else if (another condition)
4989 The braces can be omitted from simple one-line actions:
4994 We use 3-space indentation, except for continued statements which
4995 are usually indented the same as the first line of the statement
4996 plus four more spaces.
4998 For macro definitions we use 2-space indentation, always leaving the "#"
4999 in the first column.
5001 #ifndef PNG_NO_FEATURE
5002 # ifndef PNG_FEATURE_SUPPORTED
5003 # define PNG_FEATURE_SUPPORTED
5007 Comments appear with the leading "/*" at the same indentation as
5008 the statement that follows the comment:
5010 /* Single-line comment */
5013 /* This is a multiple-line
5018 Very short comments can be placed after the end of the statement
5019 to which they pertain:
5021 statement; /* comment */
5023 We don't use C++ style ("//") comments. We have, however,
5024 used them in the past in some now-abandoned MMX assembler
5027 Functions and their curly braces are not indented, and
5028 exported functions are marked with PNGAPI:
5030 /* This is a public function that is visible to
5031 * application programmers. It does thus-and-so.
5034 png_exported_function(png_ptr, png_info, foo)
5039 The prototypes for all exported functions appear in png.h,
5040 above the comment that says
5042 /* Maintainer: Put new public prototypes here ... */
5044 We mark all non-exported functions with "/* PRIVATE */"":
5047 png_non_exported_function(png_ptr, png_info, foo)
5052 The prototypes for non-exported functions (except for those in
5055 above the comment that says
5057 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
5059 To avoid polluting the global namespace, the names of all exported
5060 functions and variables begin with "png_", and all publicly visible C
5061 preprocessor macros begin with "PNG_". We request that applications that
5062 use libpng *not* begin any of their own symbols with either of these strings.
5064 We put a space after each comma and after each semicolon
5065 in "for" statements, and we put spaces before and after each
5066 C binary operator and after "for" or "while", and before
5067 "?". We don't put a space between a typecast and the expression
5068 being cast, nor do we put one between a function name and the
5069 left parenthesis that follows it:
5071 for (i = 2; i > 0; --i)
5072 y[i] = a(x) + (int)b;
5074 We prefer #ifdef and #ifndef to #if defined() and if !defined()
5075 when there is only one macro being tested.
5077 We do not use the TAB character for indentation in the C sources.
5079 Lines do not exceed 80 characters.
5081 Other rules can be inferred by inspecting the libpng source.
5083 .SH XIV. Y2K Compliance in libpng
5087 Since the PNG Development group is an ad-hoc body, we can't make
5088 an official declaration.
5090 This is your unofficial assurance that libpng from version 0.71 and
5091 upward through 1.5.2 are Y2K compliant. It is my belief that earlier
5092 versions were also Y2K compliant.
5094 Libpng only has three year fields. One is a 2-byte unsigned integer that
5095 will hold years up to 65535. The other two hold the date in text
5096 format, and will hold years up to 9999.
5099 "png_uint_16 year" in png_time_struct.
5102 "png_charp time_buffer" in png_struct and
5103 "near_time_buffer", which is a local character string in png.c.
5105 There are seven time-related functions:
5107 png_convert_to_rfc_1123() in png.c
5108 (formerly png_convert_to_rfc_1152() in error)
5109 png_convert_from_struct_tm() in pngwrite.c, called
5111 png_convert_from_time_t() in pngwrite.c
5112 png_get_tIME() in pngget.c
5113 png_handle_tIME() in pngrutil.c, called in pngread.c
5114 png_set_tIME() in pngset.c
5115 png_write_tIME() in pngwutil.c, called in pngwrite.c
5117 All appear to handle dates properly in a Y2K environment. The
5118 png_convert_from_time_t() function calls gmtime() to convert from system
5119 clock time, which returns (year - 1900), which we properly convert to
5120 the full 4-digit year. There is a possibility that applications using
5121 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5122 function, or that they are incorrectly passing only a 2-digit year
5123 instead of "year - 1900" into the png_convert_from_struct_tm() function,
5124 but this is not under our control. The libpng documentation has always
5125 stated that it works with 4-digit years, and the APIs have been
5128 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5129 integer to hold the year, and can hold years as large as 65535.
5131 zlib, upon which libpng depends, is also Y2K compliant. It contains
5132 no date-related code.
5135 Glenn Randers-Pehrson
5137 PNG Development Group
5141 Note about libpng version numbers:
5143 Due to various miscommunications, unforeseen code incompatibilities
5144 and occasional factors outside the authors' control, version numbering
5145 on the library has not always been consistent and straightforward.
5146 The following table summarizes matters since version 0.89c, which was
5147 the first widely used release:
5149 source png.h png.h shared-lib
5150 version string int version
5151 ------- ------ ----- ----------
5152 0.89c ("beta 3") 0.89 89 1.0.89
5153 0.90 ("beta 4") 0.90 90 0.90
5154 0.95 ("beta 5") 0.95 95 0.95
5155 0.96 ("beta 6") 0.96 96 0.96
5156 0.97b ("beta 7") 1.00.97 97 1.0.1
5157 0.97c 0.97 97 2.0.97
5160 0.99a-m 0.99 99 2.0.99
5162 1.0.0 1.0.0 100 2.1.0
5163 1.0.0 (from here on, the 100 2.1.0
5164 1.0.1 png.h string is 10001 2.1.0
5165 1.0.1a-e identical to the 10002 from here on, the
5166 1.0.2 source version) 10002 shared library is 2.V
5167 1.0.2a-b 10003 where V is the source
5168 1.0.1 10001 code version except as
5169 1.0.1a-e 10002 2.1.0.1a-e noted.
5171 1.0.2a-b 10003 2.1.0.2a-b
5173 1.0.3a-d 10004 2.1.0.3a-d
5175 1.0.4a-f 10005 2.1.0.4a-f
5176 1.0.5 (+ 2 patches) 10005 2.1.0.5
5177 1.0.5a-d 10006 2.1.0.5a-d
5178 1.0.5e-r 10100 2.1.0.5e-r
5179 1.0.5s-v 10006 2.1.0.5s-v
5180 1.0.6 (+ 3 patches) 10006 2.1.0.6
5181 1.0.6d-g 10007 2.1.0.6d-g
5184 1.0.6j 10007 2.1.0.6j
5185 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5186 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5187 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5188 1.0.7 1 10007 2.1.0.7
5189 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5190 1.0.8rc1 1 10008 2.1.0.8rc1
5191 1.0.8 1 10008 2.1.0.8
5192 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5193 1.0.9rc1 1 10009 2.1.0.9rc1
5194 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5195 1.0.9rc2 1 10009 2.1.0.9rc2
5196 1.0.9 1 10009 2.1.0.9
5197 1.0.10beta1 1 10010 2.1.0.10beta1
5198 1.0.10rc1 1 10010 2.1.0.10rc1
5199 1.0.10 1 10010 2.1.0.10
5200 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5201 1.0.11rc1 1 10011 2.1.0.11rc1
5202 1.0.11 1 10011 2.1.0.11
5203 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5204 1.0.12rc1 2 10012 2.1.0.12rc1
5205 1.0.12 2 10012 2.1.0.12
5206 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5207 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5208 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5209 1.2.0rc1 3 10200 3.1.2.0rc1
5210 1.2.0 3 10200 3.1.2.0
5211 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5212 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5213 1.2.1 3 10201 3.1.2.1
5214 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5215 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5216 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5217 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5218 1.0.13 10 10013 10.so.0.1.0.13
5219 1.2.2 12 10202 12.so.0.1.2.2
5220 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5221 1.2.3 12 10203 12.so.0.1.2.3
5222 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5223 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5224 1.0.14 10 10014 10.so.0.1.0.14
5225 1.2.4 13 10204 12.so.0.1.2.4
5226 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5227 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5228 1.0.15 10 10015 10.so.0.1.0.15
5229 1.2.5 13 10205 12.so.0.1.2.5
5230 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5231 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5232 1.0.16 10 10016 10.so.0.1.0.16
5233 1.2.6 13 10206 12.so.0.1.2.6
5234 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5235 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5236 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5237 1.0.17 10 10017 12.so.0.1.0.17
5238 1.2.7 13 10207 12.so.0.1.2.7
5239 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5240 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5241 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5242 1.0.18 10 10018 12.so.0.1.0.18
5243 1.2.8 13 10208 12.so.0.1.2.8
5244 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5245 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5246 1.2.9rc1 13 10209 12.so.0.9[.0]
5247 1.2.9 13 10209 12.so.0.9[.0]
5248 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5249 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5250 1.2.10 13 10210 12.so.0.10[.0]
5251 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5252 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5253 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5254 1.2.11 13 10211 12.so.0.11[.0]
5255 1.2.12 13 10212 12.so.0.12[.0]
5256 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5257 1.2.13 13 10213 12.so.0.13[.0]
5258 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5259 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5260 1.4.0rc01 14 10400 14.so.14.0[.0]
5261 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5262 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5263 1.4.0 14 10400 14.so.14.0[.0]
5264 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5265 1.4.1rc01 14 10401 14.so.14.1[.0]
5266 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5267 1.4.1 14 10401 14.so.14.1[.0]
5268 1.4.2 14 10402 14.so.14.2[.0]
5269 1.4.3 14 10403 14.so.14.3[.0]
5270 1.4.4 14 10404 14.so.14.4[.0]
5271 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5272 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5273 1.5.0 15 10500 15.so.15.0[.0]
5274 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5275 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5276 1.5.1 15 10501 15.so.15.1[.0]
5277 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5278 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5279 1.5.2 15 10502 15.so.15.2[.0]
5281 Henceforth the source version will match the shared-library minor
5282 and patch numbers; the shared-library major version number will be
5283 used for changes in backward compatibility, as it is intended. The
5284 PNG_PNGLIB_VER macro, which is not used within libpng but is available
5285 for applications, is an unsigned integer of the form xyyzz corresponding
5286 to the source version x.y.z (leading zeros in y and z). Beta versions
5287 were given the previous public release number plus a letter, until
5288 version 1.0.6j; from then on they were given the upcoming public
5289 release number plus "betaNN" or "rcN".
5292 .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5297 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5298 http://www.libpng.org/pub/png
5303 (generally) at the same location as
5307 ftp://ftp.info-zip.org/pub/infozip/zlib
5310 .IR PNG specification: RFC 2083
5312 (generally) at the same location as
5316 ftp://ds.internic.net/rfc/rfc2083.txt
5318 or (as a W3C Recommendation) at
5320 http://www.w3.org/TR/REC-png.html
5323 In the case of any inconsistency between the PNG specification
5324 and this library, the specification takes precedence.
5327 This man page: Glenn Randers-Pehrson
5328 <glennrp at users.sourceforge.net>
5330 The contributing authors would like to thank all those who helped
5331 with testing, bug fixes, and patience. This wouldn't have been
5332 possible without all of you.
5334 Thanks to Frank J. T. Wojcik for helping with the documentation.
5336 Libpng version 1.5.2 - March 31, 2011:
5337 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5338 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5340 Supported by the PNG development group
5342 png-mng-implement at lists.sf.net
5343 (subscription required; visit
5344 png-mng-implement at lists.sourceforge.net (subscription required; visit
5345 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5348 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5350 (This copy of the libpng notices is provided for your convenience. In case of
5351 any discrepancy between this copy and the notices in the file png.h that is
5352 included in the libpng distribution, the latter shall prevail.)
5354 If you modify libpng you may insert additional notices immediately following
5357 This code is released under the libpng license.
5359 libpng versions 1.2.6, August 15, 2004, through 1.5.2, March 31, 2011, are
5360 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5361 distributed according to the same disclaimer and license as libpng-1.2.5
5362 with the following individual added to the list of Contributing Authors
5366 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5367 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5368 distributed according to the same disclaimer and license as libpng-1.0.6
5369 with the following individuals added to the list of Contributing Authors
5371 Simon-Pierre Cadieux
5375 and with the following additions to the disclaimer:
5377 There is no warranty against interference with your
5378 enjoyment of the library or against infringement.
5379 There is no warranty that our efforts or the library
5380 will fulfill any of your particular purposes or needs.
5381 This library is provided with all faults, and the entire
5382 risk of satisfactory quality, performance, accuracy, and
5383 effort is with the user.
5385 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5386 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5387 Distributed according to the same disclaimer and license as libpng-0.96,
5388 with the following individuals added to the list of Contributing Authors:
5391 Glenn Randers-Pehrson
5394 libpng versions 0.89, June 1996, through 0.96, May 1997, are
5395 Copyright (c) 1996, 1997 Andreas Dilger
5396 Distributed according to the same disclaimer and license as libpng-0.88,
5397 with the following individuals added to the list of Contributing Authors:
5406 libpng versions 0.5, May 1995, through 0.88, January 1996, are
5407 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
5409 For the purposes of this copyright and license, "Contributing Authors"
5410 is defined as the following set of individuals:
5418 The PNG Reference Library is supplied "AS IS". The Contributing Authors
5419 and Group 42, Inc. disclaim all warranties, expressed or implied,
5420 including, without limitation, the warranties of merchantability and of
5421 fitness for any purpose. The Contributing Authors and Group 42, Inc.
5422 assume no liability for direct, indirect, incidental, special, exemplary,
5423 or consequential damages, which may result from the use of the PNG
5424 Reference Library, even if advised of the possibility of such damage.
5426 Permission is hereby granted to use, copy, modify, and distribute this
5427 source code, or portions hereof, for any purpose, without fee, subject
5428 to the following restrictions:
5430 1. The origin of this source code must not be misrepresented.
5432 2. Altered versions must be plainly marked as such and
5433 must not be misrepresented as being the original source.
5435 3. This Copyright notice may not be removed or altered from
5436 any source or altered source distribution.
5438 The Contributing Authors and Group 42, Inc. specifically permit, without
5439 fee, and encourage the use of this source code as a component to
5440 supporting the PNG file format in commercial products. If you use this
5441 source code in a product, acknowledgment is not required but would be
5445 A "png_get_copyright" function is available, for convenient use in "about"
5448 printf("%s",png_get_copyright(NULL));
5450 Also, the PNG logo (in PNG format, of course) is supplied in the
5451 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
5453 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
5454 certification mark of the Open Source Initiative.
5456 Glenn Randers-Pehrson
5457 glennrp at users.sourceforge.net
projects / l4.git / blob