1 .TH LIBPNG 3 "June 26, 2010"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.4.3
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_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
23 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
27 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
31 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
35 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
39 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
43 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
47 \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
51 \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
55 \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
59 \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
63 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
67 \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
71 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
75 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
79 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
83 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
87 \fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
91 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
95 \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
99 \fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
103 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
107 \fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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
111 \fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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
115 \fBpng_uint_32 png_get_chunk_cache_max (png_structp \fIpng_ptr\fP\fB);\fP
119 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
123 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
127 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
135 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
143 \fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
147 \fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
151 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
155 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
159 \fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
163 \fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
167 \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
171 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
175 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
183 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
187 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
191 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
195 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_structp \fIpng_ptr\fP\fB);\fP
199 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
203 \fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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
207 \fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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
211 \fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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
215 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
219 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
223 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
227 \fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
231 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
233 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
237 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
241 \fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
245 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
249 \fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
253 \fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
257 \fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
261 \fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
265 \fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
269 \fB/* This function is really an inline macro. \fI*/
271 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
275 \fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
279 \fB/* This function is really an inline macro. \fI*/
281 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
285 \fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
289 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
293 \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
297 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
301 \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
305 \fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
309 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
313 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
317 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
321 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
325 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
329 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
333 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
337 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
341 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
345 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
349 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
353 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
357 \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
361 \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
365 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
369 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
373 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
377 \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
381 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
385 \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
389 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
393 \fBpng_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
397 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
401 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
405 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
409 \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
413 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
417 \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
421 \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
425 \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
429 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
433 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
437 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
441 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
445 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
449 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
453 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
457 \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
461 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
465 \fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
469 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
473 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
477 \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
481 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
485 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
489 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
493 \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
497 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
501 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
505 \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
509 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
513 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
517 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
521 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
525 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
529 \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
533 \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
537 \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
541 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
545 \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
549 \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
553 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
557 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
561 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
565 \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
569 \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
573 \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
577 \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
581 \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
585 \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
589 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
593 \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
597 \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
601 \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
605 \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
609 \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
613 \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
617 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
621 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
625 \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
629 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
633 \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
637 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
641 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
645 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
649 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
653 \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
657 \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
661 \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
665 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
669 \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
673 \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
677 \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
681 \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
685 \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
689 \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
693 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
697 \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
701 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
705 \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
709 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
713 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
717 \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
721 \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
725 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
729 \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
733 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
737 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
741 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
745 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
749 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
753 \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
757 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
761 \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
765 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
769 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
773 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
780 library supports encoding, decoding, and various manipulations of
781 the Portable Network Graphics (PNG) format image files. It uses the
784 Following is a copy of the libpng.txt file that accompanies libpng.
786 libpng.txt - A description on how to use and modify libpng
788 libpng version 1.4.3 - June 26, 2010
789 Updated and distributed by Glenn Randers-Pehrson
790 <glennrp at users.sourceforge.net>
791 Copyright (c) 1998-2009 Glenn Randers-Pehrson
793 This document is released under the libpng license.
794 For conditions of distribution and use, see the disclaimer
799 libpng versions 0.97, January 1998, through 1.4.3 - June 26, 2010
800 Updated and distributed by Glenn Randers-Pehrson
801 Copyright (c) 1998-2009 Glenn Randers-Pehrson
803 libpng 1.0 beta 6 version 0.96 May 28, 1997
804 Updated and distributed by Andreas Dilger
805 Copyright (c) 1996, 1997 Andreas Dilger
807 libpng 1.0 beta 2 - version 0.88 January 26, 1996
808 For conditions of distribution and use, see copyright
809 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
810 Schalnat, Group 42, Inc.
812 Updated/rewritten per request in the libpng FAQ
813 Copyright (c) 1995, 1996 Frank J. T. Wojcik
814 December 18, 1995 & January 20, 1996
818 This file describes how to use and modify the PNG reference library
819 (known as libpng) for your own use. There are five sections to this
820 file: introduction, structures, reading, writing, and modification and
821 configuration notes for various special platforms. In addition to this
822 file, example.c is a good starting point for using the library, as
823 it is heavily commented and should include everything most people
824 will need. We assume that libpng is already installed; see the
825 INSTALL file for instructions on how to install libpng.
827 For examples of libpng usage, see the files "example.c", "pngtest.c",
828 and the files in the "contrib" directory, all of which are included in
829 the libpng distribution.
831 Libpng was written as a companion to the PNG specification, as a way
832 of reducing the amount of time and effort it takes to support the PNG
833 file format in application programs.
835 The PNG specification (second edition), November 2003, is available as
836 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
837 <http://www.w3.org/TR/2003/REC-PNG-20031110/
838 The W3C and ISO documents have identical technical content.
840 The PNG-1.2 specification is available at
841 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
842 to the PNG specification (second edition) but has some additional material.
844 The PNG-1.0 specification is available
845 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
846 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
848 Some additional chunks are described in the special-purpose public chunks
849 documents at <http://www.libpng.org/pub/png/documents/>.
852 about PNG, and the latest version of libpng, can be found at the PNG home
853 page, <http://www.libpng.org/pub/png/>.
855 Most users will not have to modify the library significantly; advanced
856 users may want to modify it more. All attempts were made to make it as
857 complete as possible, while keeping the code easy to understand.
858 Currently, this library only supports C. Support for other languages
861 Libpng has been designed to handle multiple sessions at one time,
862 to be easily modifiable, to be portable to the vast majority of
863 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
864 to use. The ultimate goal of libpng is to promote the acceptance of
865 the PNG file format in whatever way possible. While there is still
866 work to be done (see the TODO file), libpng should cover the
867 majority of the needs of its users.
869 Libpng uses zlib for its compression and decompression of PNG files.
870 Further information about zlib, and the latest version of zlib, can
871 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
872 The zlib compression utility is a general purpose utility that is
873 useful for more than PNG files, and can be used without libpng.
874 See the documentation delivered with zlib for more details.
875 You can usually find the source files for the zlib utility wherever you
876 find the libpng source files.
878 Libpng is thread safe, provided the threads are using different
879 instances of the structures. Each thread should have its own
880 png_struct and png_info instances, and thus its own image.
881 Libpng does not protect itself against two threads using the
882 same instance of a structure.
886 There are two main structures that are important to libpng, png_struct
887 and png_info. The first, png_struct, is an internal structure that
888 will not, for the most part, be used by a user except as the first
889 variable passed to every libpng function call.
891 The png_info structure is designed to provide information about the
892 PNG file. At one time, the fields of png_info were intended to be
893 directly accessible to the user. However, this tended to cause problems
894 with applications using dynamically loaded libraries, and as a result
895 a set of interface functions for png_info (the png_get_*() and png_set_*()
896 functions) was developed. The fields of png_info are still available for
897 older applications, but it is suggested that applications use the new
898 interfaces if at all possible.
900 Applications that do make direct access to the members of png_struct (except
901 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
902 and applications that make direct access to the members of png_info must
903 be recompiled if they were compiled or loaded with libpng version 1.0.6,
904 in which the members were in a different order. In version 1.0.7, the
905 members of the png_info structure reverted to the old order, as they were
906 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
907 structures are going to be hidden, and the contents of the structures will
908 only be accessible through the png_get/png_set functions.
910 The png.h header file is an invaluable reference for programming with libpng.
911 And while I'm on the topic, make sure you include the libpng header file:
917 We'll now walk you through the possible functions to call when reading
918 in a PNG file sequentially, briefly explaining the syntax and purpose
919 of each one. See example.c and png.h for more detail. While
920 progressive reading is covered in the next section, you will still
921 need some of the functions discussed in this section to read a PNG
926 You will want to do the I/O initialization(*) before you get into libpng,
927 so if it doesn't work, you don't have much to undo. Of course, you
928 will also want to insure that you are, in fact, dealing with a PNG
929 file. Libpng provides a simple check to see if a file is a PNG file.
930 To use it, pass in the first 1 to 8 bytes of the file to the function
931 png_sig_cmp(), and it will return 0 (false) if the bytes match the
932 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
933 Of course, the more bytes you pass in, the greater the accuracy of the
936 If you are intending to keep the file pointer open for use in libpng,
937 you must ensure you don't read more than 8 bytes from the beginning
938 of the file, and you also have to make a call to png_set_sig_bytes_read()
939 with the number of bytes you read from the beginning. Libpng will
940 then only check the bytes (if any) that your program didn't read.
942 (*): If you are not using the standard I/O functions, you will need
943 to replace them with custom functions. See the discussion under
947 FILE *fp = fopen(file_name, "rb");
952 fread(header, 1, number, fp);
953 is_png = !png_sig_cmp(header, 0, number);
960 Next, png_struct and png_info need to be allocated and initialized. In
961 order to ensure that the size of these structures is correct even with a
962 dynamically linked libpng, there are functions to initialize and
963 allocate the structures. We also pass the library version, optional
964 pointers to error handling functions, and a pointer to a data struct for
965 use by the error functions, if necessary (the pointer and functions can
966 be NULL if the default error handlers are to be used). See the section
967 on Changes to Libpng below regarding the old initialization functions.
968 The structure allocation functions quietly return NULL if they fail to
969 create the structure, so your application should check for that.
971 png_structp png_ptr = png_create_read_struct
972 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
973 user_error_fn, user_warning_fn);
977 png_infop info_ptr = png_create_info_struct(png_ptr);
980 png_destroy_read_struct(&png_ptr,
981 (png_infopp)NULL, (png_infopp)NULL);
985 png_infop end_info = png_create_info_struct(png_ptr);
988 png_destroy_read_struct(&png_ptr, &info_ptr,
993 If you want to use your own memory allocation routines,
994 define PNG_USER_MEM_SUPPORTED and use
995 png_create_read_struct_2() instead of png_create_read_struct():
997 png_structp png_ptr = png_create_read_struct_2
998 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
999 user_error_fn, user_warning_fn, (png_voidp)
1000 user_mem_ptr, user_malloc_fn, user_free_fn);
1002 The error handling routines passed to png_create_read_struct()
1003 and the memory alloc/free routines passed to png_create_struct_2()
1004 are only necessary if you are not using the libpng supplied error
1005 handling and memory alloc/free functions.
1007 When libpng encounters an error, it expects to longjmp back
1008 to your routine. Therefore, you will need to call setjmp and pass
1009 your png_jmpbuf(png_ptr). If you read the file from different
1010 routines, you will need to update the jmpbuf field every time you enter
1011 a new routine that will call a png_*() function.
1013 See your documentation of setjmp/longjmp for your compiler for more
1014 information on setjmp/longjmp. See the discussion on libpng error
1015 handling in the Customizing Libpng section below for more information
1016 on the libpng error handling. If an error occurs, and libpng longjmp's
1017 back to your setjmp, you will want to call png_destroy_read_struct() to
1020 if (setjmp(png_jmpbuf(png_ptr)))
1022 png_destroy_read_struct(&png_ptr, &info_ptr,
1028 If you would rather avoid the complexity of setjmp/longjmp issues,
1029 you can compile libpng with PNG_NO_SETJMP, in which case
1030 errors will result in a call to PNG_ABORT() which defaults to abort().
1032 You can #define PNG_ABORT() to a function that does something
1033 more useful than abort(), as long as your function does not
1036 Now you need to set up the input code. The default for libpng is to
1037 use the C function fread(). If you use this, you will need to pass a
1038 valid FILE * in the function png_init_io(). Be sure that the file is
1039 opened in binary mode. If you wish to handle reading data in another
1040 way, you need not call the png_init_io() function, but you must then
1041 implement the libpng I/O methods discussed in the Customizing Libpng
1044 png_init_io(png_ptr, fp);
1046 If you had previously opened the file and read any of the signature from
1047 the beginning in order to see if this was a PNG file, you need to let
1048 libpng know that there are some bytes missing from the start of the file.
1050 png_set_sig_bytes(png_ptr, number);
1052 You can change the zlib compression buffer size to be used while
1053 reading compressed data with
1055 png_set_compression_buffer_size(png_ptr, buffer_size);
1057 where the default size is 8192 bytes. Note that the buffer size
1058 is changed immediately and the buffer is reallocated immediately,
1059 instead of setting a flag to be acted upon later.
1061 .SS Setting up callback code
1063 You can set up a callback function to handle any unknown chunks in the
1064 input stream. You must supply the function
1066 read_chunk_callback(png_ptr ptr,
1067 png_unknown_chunkp chunk);
1069 /* The unknown chunk structure contains your
1070 chunk data, along with similar data for any other
1077 /* Note that libpng has already taken care of
1080 /* put your code here. Search for your chunk in the
1081 unknown chunk structure, process it, and return one
1082 of the following: */
1084 return (-n); /* chunk had an error */
1085 return (0); /* did not recognize */
1086 return (n); /* success */
1089 (You can give your function another name that you like instead of
1090 "read_chunk_callback")
1092 To inform libpng about your function, use
1094 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1095 read_chunk_callback);
1097 This names not only the callback function, but also a user pointer that
1098 you can retrieve with
1100 png_get_user_chunk_ptr(png_ptr);
1102 If you call the png_set_read_user_chunk_fn() function, then all unknown
1103 chunks will be saved when read, in case your callback function will need
1104 one or more of them. This behavior can be changed with the
1105 png_set_keep_unknown_chunks() function, described below.
1107 At this point, you can set up a callback function that will be
1108 called after each row has been read, which you can use to control
1109 a progress meter or the like. It's demonstrated in pngtest.c.
1110 You must supply a function
1112 void read_row_callback(png_ptr ptr, png_uint_32 row,
1115 /* put your code here */
1118 (You can give it another name that you like instead of "read_row_callback")
1120 To inform libpng about your function, use
1122 png_set_read_status_fn(png_ptr, read_row_callback);
1124 .SS Unknown-chunk handling
1126 Now you get to set the way the library processes unknown chunks in the
1127 input PNG stream. Both known and unknown chunks will be read. Normal
1128 behavior is that known chunks will be parsed into information in
1129 various info_ptr members while unknown chunks will be discarded. This
1130 behavior can be wasteful if your application will never use some known
1131 chunk types. To change this, you can call:
1133 png_set_keep_unknown_chunks(png_ptr, keep,
1134 chunk_list, num_chunks);
1135 keep - 0: default unknown chunk handling
1136 1: ignore; do not keep
1137 2: keep only if safe-to-copy
1138 3: keep even if unsafe-to-copy
1139 You can use these definitions:
1140 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1141 PNG_HANDLE_CHUNK_NEVER 1
1142 PNG_HANDLE_CHUNK_IF_SAFE 2
1143 PNG_HANDLE_CHUNK_ALWAYS 3
1144 chunk_list - list of chunks affected (a byte string,
1145 five bytes per chunk, NULL or '\0' if
1147 num_chunks - number of chunks affected; if 0, all
1148 unknown chunks are affected. If nonzero,
1149 only the chunks in the list are affected
1151 Unknown chunks declared in this way will be saved as raw data onto a
1152 list of png_unknown_chunk structures. If a chunk that is normally
1153 known to libpng is named in the list, it will be handled as unknown,
1154 according to the "keep" directive. If a chunk is named in successive
1155 instances of png_set_keep_unknown_chunks(), the final instance will
1156 take precedence. The IHDR and IEND chunks should not be named in
1157 chunk_list; if they are, libpng will process them normally anyway.
1159 Here is an example of the usage of png_set_keep_unknown_chunks(),
1160 where the private "vpAg" chunk will later be processed by a user chunk
1163 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1165 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1166 png_byte unused_chunks[]=
1168 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1169 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1170 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1171 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1172 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1173 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1179 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1180 /* ignore all unknown chunks: */
1181 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1182 /* except for vpAg: */
1183 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1184 /* also ignore unused known chunks: */
1185 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1186 (int)sizeof(unused_chunks)/5);
1191 The PNG specification allows the width and height of an image to be as
1192 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1193 Since very few applications really need to process such large images,
1194 we have imposed an arbitrary 1-million limit on rows and columns.
1195 Larger images will be rejected immediately with a png_error() call. If
1196 you wish to override this limit, you can use
1198 png_set_user_limits(png_ptr, width_max, height_max);
1200 to set your own limits, or use width_max = height_max = 0x7fffffffL
1201 to allow all valid dimensions (libpng may reject some very large images
1202 anyway because of potential buffer overflow conditions).
1204 You should put this statement after you create the PNG structure and
1205 before calling png_read_info(), png_read_png(), or png_process_data().
1206 If you need to retrieve the limits that are being applied, use
1208 width_max = png_get_user_width_max(png_ptr);
1209 height_max = png_get_user_height_max(png_ptr);
1211 The PNG specification sets no limit on the number of ancillary chunks
1212 allowed in a PNG datastream. You can impose a limit on the total number
1213 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1215 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1217 where 0x7fffffffL means unlimited. You can retrieve this limit with
1219 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1221 This limit also applies to the number of buffers that can be allocated
1222 by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1224 You can also set a limit on the amount of memory that a compressed chunk
1225 other than IDAT can occupy, with
1227 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1229 and you can retrieve the limit with
1231 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1233 Any chunks that would cause either of these limits to be exceeded will
1236 .SS The high-level read interface
1238 At this point there are two ways to proceed; through the high-level
1239 read interface, or through a sequence of low-level read operations.
1240 You can use the high-level interface if (a) you are willing to read
1241 the entire image into memory, and (b) the input transformations
1242 you want to do are limited to the following set:
1244 PNG_TRANSFORM_IDENTITY No transformation
1245 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1247 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1248 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1250 PNG_TRANSFORM_PACKSWAP Change order of packed
1252 PNG_TRANSFORM_EXPAND Perform set_expand()
1253 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1254 PNG_TRANSFORM_SHIFT Normalize pixels to the
1256 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1258 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1260 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1262 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1263 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1264 to RGB (or GA to RGBA)
1266 (This excludes setting a background color, doing gamma transformation,
1267 quantizing, and setting filler.) If this is the case, simply do this:
1269 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1271 where png_transforms is an integer containing the bitwise OR of some
1272 set of transformation flags. This call is equivalent to png_read_info(),
1273 followed the set of transformations indicated by the transform mask,
1274 then png_read_image(), and finally png_read_end().
1276 (The final parameter of this call is not yet used. Someday it might point
1277 to transformation parameters required by some future input transform.)
1279 You must use png_transforms and not call any png_set_transform() functions
1280 when you use png_read_png().
1282 After you have called png_read_png(), you can retrieve the image data
1285 row_pointers = png_get_rows(png_ptr, info_ptr);
1287 where row_pointers is an array of pointers to the pixel data for each row:
1289 png_bytep row_pointers[height];
1291 If you know your image size and pixel size ahead of time, you can allocate
1292 row_pointers prior to calling png_read_png() with
1294 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1296 "Image is too tall to process in memory");
1297 if (width > PNG_UINT_32_MAX/pixel_size)
1299 "Image is too wide to process in memory");
1300 row_pointers = png_malloc(png_ptr,
1301 height*png_sizeof(png_bytep));
1302 for (int i=0; i<height, i++)
1303 row_pointers[i]=NULL; /* security precaution */
1304 for (int i=0; i<height, i++)
1305 row_pointers[i]=png_malloc(png_ptr,
1307 png_set_rows(png_ptr, info_ptr, &row_pointers);
1309 Alternatively you could allocate your image in one big block and define
1310 row_pointers[i] to point into the proper places in your block.
1312 If you use png_set_rows(), the application is responsible for freeing
1313 row_pointers (and row_pointers[i], if they were separately allocated).
1315 If you don't allocate row_pointers ahead of time, png_read_png() will
1316 do it, and it'll be free'ed when you call png_destroy_*().
1318 .SS The low-level read interface
1320 If you are going the low-level route, you are now ready to read all
1321 the file information up to the actual image data. You do this with a
1322 call to png_read_info().
1324 png_read_info(png_ptr, info_ptr);
1326 This will process all chunks up to but not including the image data.
1328 .SS Querying the info structure
1330 Functions are used to get the information from the info_ptr once it
1331 has been read. Note that these fields may not be completely filled
1332 in until png_read_end() has read the chunk data following the image.
1334 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1335 &bit_depth, &color_type, &interlace_type,
1336 &compression_type, &filter_method);
1338 width - holds the width of the image
1339 in pixels (up to 2^31).
1340 height - holds the height of the image
1341 in pixels (up to 2^31).
1342 bit_depth - holds the bit depth of one of the
1343 image channels. (valid values are
1344 1, 2, 4, 8, 16 and depend also on
1345 the color_type. See also
1346 significant bits (sBIT) below).
1347 color_type - describes which color/alpha channels
1350 (bit depths 1, 2, 4, 8, 16)
1351 PNG_COLOR_TYPE_GRAY_ALPHA
1353 PNG_COLOR_TYPE_PALETTE
1354 (bit depths 1, 2, 4, 8)
1357 PNG_COLOR_TYPE_RGB_ALPHA
1360 PNG_COLOR_MASK_PALETTE
1361 PNG_COLOR_MASK_COLOR
1362 PNG_COLOR_MASK_ALPHA
1364 filter_method - (must be PNG_FILTER_TYPE_BASE
1365 for PNG 1.0, and can also be
1366 PNG_INTRAPIXEL_DIFFERENCING if
1367 the PNG datastream is embedded in
1368 a MNG-1.0 datastream)
1369 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1371 interlace_type - (PNG_INTERLACE_NONE or
1372 PNG_INTERLACE_ADAM7)
1374 Any or all of interlace_type, compression_type, or
1375 filter_method can be NULL if you are
1376 not interested in their values.
1378 Note that png_get_IHDR() returns 32-bit data into
1379 the application's width and height variables.
1380 This is an unsafe situation if these are 16-bit
1381 variables. In such situations, the
1382 png_get_image_width() and png_get_image_height()
1383 functions described below are safer.
1385 width = png_get_image_width(png_ptr,
1387 height = png_get_image_height(png_ptr,
1389 bit_depth = png_get_bit_depth(png_ptr,
1391 color_type = png_get_color_type(png_ptr,
1393 filter_method = png_get_filter_type(png_ptr,
1395 compression_type = png_get_compression_type(png_ptr,
1397 interlace_type = png_get_interlace_type(png_ptr,
1400 channels = png_get_channels(png_ptr, info_ptr);
1401 channels - number of channels of info for the
1402 color type (valid values are 1 (GRAY,
1403 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1404 4 (RGB_ALPHA or RGB + filler byte))
1405 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1406 rowbytes - number of bytes needed to hold a row
1408 signature = png_get_signature(png_ptr, info_ptr);
1409 signature - holds the signature read from the
1410 file (if any). The data is kept in
1411 the same offset it would be if the
1412 whole signature were read (i.e. if an
1413 application had already read in 4
1414 bytes of signature before starting
1415 libpng, the remaining 4 bytes would
1416 be in signature[4] through signature[7]
1417 (see png_set_sig_bytes())).
1419 These are also important, but their validity depends on whether the chunk
1420 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1421 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1422 data has been read, or zero if it is missing. The parameters to the
1423 png_get_<chunk> are set directly if they are simple data types, or a
1424 pointer into the info_ptr is returned for any complex types.
1426 png_get_PLTE(png_ptr, info_ptr, &palette,
1428 palette - the palette for the file
1429 (array of png_color)
1430 num_palette - number of entries in the palette
1432 png_get_gAMA(png_ptr, info_ptr, &gamma);
1433 gamma - the gamma the file is written
1436 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1437 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1438 The presence of the sRGB chunk
1439 means that the pixel data is in the
1440 sRGB color space. This chunk also
1441 implies specific values of gAMA and
1444 png_get_iCCP(png_ptr, info_ptr, &name,
1445 &compression_type, &profile, &proflen);
1446 name - The profile name.
1447 compression - The compression type; always
1448 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1449 You may give NULL to this argument to
1451 profile - International Color Consortium color
1452 profile data. May contain NULs.
1453 proflen - length of profile data in bytes.
1455 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1456 sig_bit - the number of significant bits for
1457 (PNG_INFO_sBIT) each of the gray,
1458 red, green, and blue channels,
1459 whichever are appropriate for the
1460 given color type (png_color_16)
1462 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1463 &num_trans, &trans_color);
1464 trans_alpha - array of alpha (transparency)
1465 entries for palette (PNG_INFO_tRNS)
1466 trans_color - graylevel or color sample values of
1467 the single transparent color for
1468 non-paletted images (PNG_INFO_tRNS)
1469 num_trans - number of transparent entries
1472 png_get_hIST(png_ptr, info_ptr, &hist);
1474 hist - histogram of palette (array of
1477 png_get_tIME(png_ptr, info_ptr, &mod_time);
1478 mod_time - time image was last modified
1481 png_get_bKGD(png_ptr, info_ptr, &background);
1482 background - background color (PNG_VALID_bKGD)
1483 valid 16-bit red, green and blue
1484 values, regardless of color_type
1486 num_comments = png_get_text(png_ptr, info_ptr,
1487 &text_ptr, &num_text);
1488 num_comments - number of comments
1489 text_ptr - array of png_text holding image
1491 text_ptr[i].compression - type of compression used
1492 on "text" PNG_TEXT_COMPRESSION_NONE
1493 PNG_TEXT_COMPRESSION_zTXt
1494 PNG_ITXT_COMPRESSION_NONE
1495 PNG_ITXT_COMPRESSION_zTXt
1496 text_ptr[i].key - keyword for comment. Must contain
1498 text_ptr[i].text - text comments for current
1499 keyword. Can be empty.
1500 text_ptr[i].text_length - length of text string,
1501 after decompression, 0 for iTXt
1502 text_ptr[i].itxt_length - length of itxt string,
1503 after decompression, 0 for tEXt/zTXt
1504 text_ptr[i].lang - language of comment (empty
1505 string for unknown).
1506 text_ptr[i].lang_key - keyword in UTF-8
1507 (empty string for unknown).
1508 Note that the itxt_length, lang, and lang_key
1509 members of the text_ptr structure only exist
1510 when the library is built with iTXt chunk support.
1512 num_text - number of comments (same as
1513 num_comments; you can put NULL here
1514 to avoid the duplication)
1515 Note while png_set_text() will accept text, language,
1516 and translated keywords that can be NULL pointers, the
1517 structure returned by png_get_text will always contain
1518 regular zero-terminated C strings. They might be
1519 empty strings but they will never be NULL pointers.
1521 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1523 palette_ptr - array of palette structures holding
1524 contents of one or more sPLT chunks
1526 num_spalettes - number of sPLT chunks read.
1528 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1530 offset_x - positive offset from the left edge
1532 offset_y - positive offset from the top edge
1534 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1536 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1538 res_x - pixels/unit physical resolution in
1540 res_y - pixels/unit physical resolution in
1542 unit_type - PNG_RESOLUTION_UNKNOWN,
1543 PNG_RESOLUTION_METER
1545 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1547 unit - physical scale units (an integer)
1548 width - width of a pixel in physical scale units
1549 height - height of a pixel in physical scale units
1550 (width and height are doubles)
1552 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1554 unit - physical scale units (an integer)
1555 width - width of a pixel in physical scale units
1556 height - height of a pixel in physical scale units
1557 (width and height are strings like "2.54")
1559 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1560 info_ptr, &unknowns)
1561 unknowns - array of png_unknown_chunk
1562 structures holding unknown chunks
1563 unknowns[i].name - name of unknown chunk
1564 unknowns[i].data - data of unknown chunk
1565 unknowns[i].size - size of unknown chunk's data
1566 unknowns[i].location - position of chunk in file
1568 The value of "i" corresponds to the order in which the
1569 chunks were read from the PNG file or inserted with the
1570 png_set_unknown_chunks() function.
1572 The data from the pHYs chunk can be retrieved in several convenient
1575 res_x = png_get_x_pixels_per_meter(png_ptr,
1577 res_y = png_get_y_pixels_per_meter(png_ptr,
1579 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1581 res_x = png_get_x_pixels_per_inch(png_ptr,
1583 res_y = png_get_y_pixels_per_inch(png_ptr,
1585 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1587 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1590 (Each of these returns 0 [signifying "unknown"] if
1591 the data is not present or if res_x is 0;
1592 res_x_and_y is 0 if res_x != res_y)
1594 The data from the oFFs chunk can be retrieved in several convenient
1597 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1598 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1599 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1600 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1602 (Each of these returns 0 [signifying "unknown" if both
1603 x and y are 0] if the data is not present or if the
1604 chunk is present but the unit is the pixel)
1606 For more information, see the png_info definition in png.h and the
1607 PNG specification for chunk contents. Be careful with trusting
1608 rowbytes, as some of the transformations could increase the space
1609 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1610 See png_read_update_info(), below.
1612 A quick word about text_ptr and num_text. PNG stores comments in
1613 keyword/text pairs, one pair per chunk, with no limit on the number
1614 of text chunks, and a 2^31 byte limit on their size. While there are
1615 suggested keywords, there is no requirement to restrict the use to these
1616 strings. It is strongly suggested that keywords and text be sensible
1617 to humans (that's the point), so don't use abbreviations. Non-printing
1618 symbols are not allowed. See the PNG specification for more details.
1619 There is also no requirement to have text after the keyword.
1621 Keywords should be limited to 79 Latin-1 characters without leading or
1622 trailing spaces, but non-consecutive spaces are allowed within the
1623 keyword. It is possible to have the same keyword any number of times.
1624 The text_ptr is an array of png_text structures, each holding a
1625 pointer to a language string, a pointer to a keyword and a pointer to
1626 a text string. The text string, language code, and translated
1627 keyword may be empty or NULL pointers. The keyword/text
1628 pairs are put into the array in the order that they are received.
1629 However, some or all of the text chunks may be after the image, so, to
1630 make sure you have read all the text chunks, don't mess with these
1631 until after you read the stuff after the image. This will be
1632 mentioned again below in the discussion that goes with png_read_end().
1634 .SS Input transformations
1636 After you've read the header information, you can set up the library
1637 to handle any special transformations of the image data. The various
1638 ways to transform the data will be described in the order that they
1639 should occur. This is important, as some of these change the color
1640 type and/or bit depth of the data, and some others only work on
1641 certain color types and bit depths. Even though each transformation
1642 checks to see if it has data that it can do something with, you should
1643 make sure to only enable a transformation if it will be valid for the
1644 data. For example, don't swap red and blue on grayscale data.
1646 The colors used for the background and transparency values should be
1647 supplied in the same format/depth as the current image data. They
1648 are stored in the same format/depth as the image data in a bKGD or tRNS
1649 chunk, so this is what libpng expects for this data. The colors are
1650 transformed to keep in sync with the image data when an application
1651 calls the png_read_update_info() routine (see below).
1653 Data will be decoded into the supplied row buffers packed into bytes
1654 unless the library has been told to transform it into another format.
1655 For example, 4 bit/pixel paletted or grayscale data will be returned
1656 2 pixels/byte with the leftmost pixel in the high-order bits of the
1657 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1658 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1659 is called to insert filler bytes, either before or after each RGB triplet.
1660 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1661 byte of the color value first, unless png_set_strip_16() is called to
1662 transform it to regular RGB RGB triplets, or png_set_filler() or
1663 png_set_add alpha() is called to insert filler bytes, either before or
1664 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1666 png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1668 The following code transforms grayscale images of less than 8 to 8 bits,
1669 changes paletted images to RGB, and adds a full alpha channel if there is
1670 transparency information in a tRNS chunk. This is most useful on
1671 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1672 viewing application that wishes to treat all images in the same way.
1674 if (color_type == PNG_COLOR_TYPE_PALETTE)
1675 png_set_palette_to_rgb(png_ptr);
1677 if (color_type == PNG_COLOR_TYPE_GRAY &&
1678 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1680 if (png_get_valid(png_ptr, info_ptr,
1681 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1683 These three functions are actually aliases for png_set_expand(), added
1684 in libpng version 1.0.4, with the function names expanded to improve code
1685 readability. In some future version they may actually do different
1688 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1689 added. It expands the sample depth without changing tRNS to alpha.
1691 As of libpng version 1.4.3, not all possible expansions are supported.
1693 In the following table, the 01 means grayscale with depth<8, 31 means
1694 indexed with depth<8, other numerals represent the color type, "T" means
1695 the tRNS chunk is present, A means an alpha channel is present, and O
1696 means tRNS or alpha is present but all pixels in the image are opaque.
1698 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
1717 "-" means the transformation is not supported.
1718 "X" means the transformation is obtained by png_set_expand().
1719 "1" means the transformation is obtained by
1720 png_set_expand_gray_1_2_4_to_8
1721 "G" means the transformation is obtained by
1722 png_set_gray_to_rgb().
1723 "P" means the transformation is obtained by
1724 png_set_expand_palette_to_rgb().
1725 "T" means the transformation is obtained by
1726 png_set_tRNS_to_alpha().
1728 PNG can have files with 16 bits per channel. If you only can handle
1729 8 bits per channel, this will strip the pixels down to 8 bit.
1731 if (bit_depth == 16)
1732 png_set_strip_16(png_ptr);
1734 If, for some reason, you don't need the alpha channel on an image,
1735 and you want to remove it rather than combining it with the background
1736 (but the image author certainly had in mind that you *would* combine
1737 it with the background, so that's what you should probably do):
1739 if (color_type & PNG_COLOR_MASK_ALPHA)
1740 png_set_strip_alpha(png_ptr);
1742 In PNG files, the alpha channel in an image
1743 is the level of opacity. If you need the alpha channel in an image to
1744 be the level of transparency instead of opacity, you can invert the
1745 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1746 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1747 images) is fully transparent, with
1749 png_set_invert_alpha(png_ptr);
1751 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1752 they can, resulting in, for example, 8 pixels per byte for 1 bit
1753 files. This code expands to 1 pixel per byte without changing the
1754 values of the pixels:
1757 png_set_packing(png_ptr);
1759 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1760 stored in a PNG image have been "scaled" or "shifted" up to the next
1761 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
1762 to 8 bits/sample in the range [0, 255]). However, it is also possible
1763 to convert the PNG pixel data back to the original bit depth of the
1764 image. This call reduces the pixels back down to the original bit depth:
1766 png_color_8p sig_bit;
1768 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1769 png_set_shift(png_ptr, sig_bit);
1771 PNG files store 3-color pixels in red, green, blue order. This code
1772 changes the storage of the pixels to blue, green, red:
1774 if (color_type == PNG_COLOR_TYPE_RGB ||
1775 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1776 png_set_bgr(png_ptr);
1778 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1779 into 4 or 8 bytes for windowing systems that need them in this format:
1781 if (color_type == PNG_COLOR_TYPE_RGB)
1782 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1784 where "filler" is the 8 or 16-bit number to fill with, and the location is
1785 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1786 you want the filler before the RGB or after. This transformation
1787 does not affect images that already have full alpha channels. To add an
1788 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1789 will generate RGBA pixels.
1791 Note that png_set_filler() does not change the color type. If you want
1792 to do that, you can add a true alpha channel with
1794 if (color_type == PNG_COLOR_TYPE_RGB ||
1795 color_type == PNG_COLOR_TYPE_GRAY)
1796 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1798 where "filler" contains the alpha value to assign to each pixel.
1799 This function was added in libpng-1.2.7.
1801 If you are reading an image with an alpha channel, and you need the
1802 data as ARGB instead of the normal PNG format RGBA:
1804 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1805 png_set_swap_alpha(png_ptr);
1807 For some uses, you may want a grayscale image to be represented as
1808 RGB. This code will do that conversion:
1810 if (color_type == PNG_COLOR_TYPE_GRAY ||
1811 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1812 png_set_gray_to_rgb(png_ptr);
1814 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1817 if (color_type == PNG_COLOR_TYPE_RGB ||
1818 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1819 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1820 int red_weight, int green_weight);
1822 error_action = 1: silently do the conversion
1823 error_action = 2: issue a warning if the original
1824 image has any pixel where
1825 red != green or red != blue
1826 error_action = 3: issue an error and abort the
1827 conversion if the original
1828 image has any pixel where
1829 red != green or red != blue
1831 red_weight: weight of red component times 100000
1832 green_weight: weight of green component times 100000
1833 If either weight is negative, default
1834 weights (21268, 71514) are used.
1836 If you have set error_action = 1 or 2, you can
1837 later check whether the image really was gray, after processing
1838 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1839 It will return a png_byte that is zero if the image was gray or
1840 1 if there were any non-gray pixels. bKGD and sBIT data
1841 will be silently converted to grayscale, using the green channel
1842 data, regardless of the error_action setting.
1844 With red_weight+green_weight<=100000,
1845 the normalized graylevel is computed:
1847 int rw = red_weight * 65536;
1848 int gw = green_weight * 65536;
1849 int bw = 65536 - (rw + gw);
1850 gray = (rw*red + gw*green + bw*blue)/65536;
1852 The default values approximate those recommended in the Charles
1853 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1854 Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1856 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1858 Libpng approximates this with
1860 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1862 which can be expressed with integers as
1864 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1866 The calculation is done in a linear colorspace, if the image gamma
1869 If you have a grayscale and you are using png_set_expand_depth(),
1870 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1871 a higher bit-depth, you must either supply the background color as a gray
1872 value at the original file bit-depth (need_expand = 1) or else supply the
1873 background color as an RGB triplet at the final, expanded bit depth
1874 (need_expand = 0). Similarly, if you are reading a paletted image, you
1875 must either supply the background color as a palette index (need_expand = 1)
1876 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1878 png_color_16 my_background;
1879 png_color_16p image_background;
1881 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1882 png_set_background(png_ptr, image_background,
1883 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1885 png_set_background(png_ptr, &my_background,
1886 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1888 The png_set_background() function tells libpng to composite images
1889 with alpha or simple transparency against the supplied background
1890 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1891 you may use this color, or supply another color more suitable for
1892 the current display (e.g., the background color from a web page). You
1893 need to tell libpng whether the color is in the gamma space of the
1894 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1895 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1896 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1897 know why anyone would use this, but it's here).
1899 To properly display PNG images on any kind of system, the application needs
1900 to know what the display gamma is. Ideally, the user will know this, and
1901 the application will allow them to set it. One method of allowing the user
1902 to set the display gamma separately for each system is to check for a
1903 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1906 Note that display_gamma is the overall gamma correction required to produce
1907 pleasing results, which depends on the lighting conditions in the surrounding
1908 environment. In a dim or brightly lit room, no compensation other than
1909 the physical gamma exponent of the monitor is needed, while in a dark room
1910 a slightly smaller exponent is better.
1912 double gamma, screen_gamma;
1914 if (/* We have a user-defined screen
1917 screen_gamma = user_defined_screen_gamma;
1919 /* One way that applications can share the same
1920 screen gamma value */
1921 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1924 screen_gamma = (double)atof(gamma_str);
1926 /* If we don't have another value */
1929 screen_gamma = 2.2; /* A good guess for a
1930 PC monitor in a bright office or a dim room */
1931 screen_gamma = 2.0; /* A good guess for a
1932 PC monitor in a dark room */
1933 screen_gamma = 1.7 or 1.0; /* A good
1934 guess for Mac systems */
1937 The png_set_gamma() function handles gamma transformations of the data.
1938 Pass both the file gamma and the current screen_gamma. If the file does
1939 not have a gamma value, you can pass one anyway if you have an idea what
1940 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1941 that file gammas are inverted from screen gammas. See the discussions
1942 on gamma in the PNG specification for an excellent description of what
1943 gamma is, and why all applications should support it. It is strongly
1944 recommended that PNG viewers support gamma correction.
1946 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1947 png_set_gamma(png_ptr, screen_gamma, gamma);
1949 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1951 If you need to reduce an RGB file to a paletted file, or if a paletted
1952 file has more entries then will fit on your screen, png_set_quantize()
1953 will do that. Note that this is a simple match dither that merely
1954 finds the closest color available. This should work fairly well with
1955 optimized palettes, and fairly badly with linear color cubes. If you
1956 pass a palette that is larger then maximum_colors, the file will
1957 reduce the number of colors in the palette so it will fit into
1958 maximum_colors. If there is a histogram, it will use it to make
1959 more intelligent choices when reducing the palette. If there is no
1960 histogram, it may not do as good a job.
1962 if (color_type & PNG_COLOR_MASK_COLOR)
1964 if (png_get_valid(png_ptr, info_ptr,
1967 png_uint_16p histogram = NULL;
1969 png_get_hIST(png_ptr, info_ptr,
1971 png_set_quantize(png_ptr, palette, num_palette,
1972 max_screen_colors, histogram, 1);
1976 png_color std_color_cube[MAX_SCREEN_COLORS] =
1979 png_set_quantize(png_ptr, std_color_cube,
1980 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1985 PNG files describe monochrome as black being zero and white being one.
1986 The following code will reverse this (make black be one and white be
1989 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1990 png_set_invert_mono(png_ptr);
1992 This function can also be used to invert grayscale and gray-alpha images:
1994 if (color_type == PNG_COLOR_TYPE_GRAY ||
1995 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1996 png_set_invert_mono(png_ptr);
1998 PNG files store 16 bit pixels in network byte order (big-endian,
1999 ie. most significant bits first). This code changes the storage to the
2000 other way (little-endian, i.e. least significant bits first, the
2001 way PCs store them):
2003 if (bit_depth == 16)
2004 png_set_swap(png_ptr);
2006 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2007 need to change the order the pixels are packed into bytes, you can use:
2010 png_set_packswap(png_ptr);
2012 Finally, you can write your own transformation function if none of
2013 the existing ones meets your needs. This is done by setting a callback
2016 png_set_read_user_transform_fn(png_ptr,
2019 You must supply the function
2021 void read_transform_fn(png_ptr ptr, row_info_ptr
2022 row_info, png_bytep data)
2024 See pngtest.c for a working example. Your function will be called
2025 after all of the other transformations have been processed.
2027 You can also set up a pointer to a user structure for use by your
2028 callback function, and you can inform libpng that your transform
2029 function will change the number of channels or bit depth with the
2032 png_set_user_transform_info(png_ptr, user_ptr,
2033 user_depth, user_channels);
2035 The user's application, not libpng, is responsible for allocating and
2036 freeing any memory required for the user structure.
2038 You can retrieve the pointer via the function
2039 png_get_user_transform_ptr(). For example:
2041 voidp read_user_transform_ptr =
2042 png_get_user_transform_ptr(png_ptr);
2044 The last thing to handle is interlacing; this is covered in detail below,
2045 but you must call the function here if you want libpng to handle expansion
2046 of the interlaced image.
2048 number_of_passes = png_set_interlace_handling(png_ptr);
2050 After setting the transformations, libpng can update your png_info
2051 structure to reflect any transformations you've requested with this
2052 call. This is most useful to update the info structure's rowbytes
2053 field so you can use it to allocate your image memory. This function
2054 will also update your palette with the correct screen_gamma and
2055 background if these have been given with the calls above.
2057 png_read_update_info(png_ptr, info_ptr);
2059 After you call png_read_update_info(), you can allocate any
2060 memory you need to hold the image. The row data is simply
2061 raw byte data for all forms of images. As the actual allocation
2062 varies among applications, no example will be given. If you
2063 are allocating one large chunk, you will need to build an
2064 array of pointers to each row, as it will be needed for some
2065 of the functions below.
2067 .SS Reading image data
2069 After you've allocated memory, you can read the image data.
2070 The simplest way to do this is in one function call. If you are
2071 allocating enough memory to hold the whole image, you can just
2072 call png_read_image() and libpng will read in all the image data
2073 and put it in the memory area supplied. You will need to pass in
2074 an array of pointers to each row.
2076 This function automatically handles interlacing, so you don't need
2077 to call png_set_interlace_handling() or call this function multiple
2078 times, or any of that other stuff necessary with png_read_rows().
2080 png_read_image(png_ptr, row_pointers);
2082 where row_pointers is:
2084 png_bytep row_pointers[height];
2086 You can point to void or char or whatever you use for pixels.
2088 If you don't want to read in the whole image at once, you can
2089 use png_read_rows() instead. If there is no interlacing (check
2090 interlace_type == PNG_INTERLACE_NONE), this is simple:
2092 png_read_rows(png_ptr, row_pointers, NULL,
2095 where row_pointers is the same as in the png_read_image() call.
2097 If you are doing this just one row at a time, you can do this with
2098 a single row_pointer instead of an array of row_pointers:
2100 png_bytep row_pointer = row;
2101 png_read_row(png_ptr, row_pointer, NULL);
2103 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2104 get somewhat harder. The only current (PNG Specification version 1.2)
2105 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
2106 is a somewhat complicated 2D interlace scheme, known as Adam7, that
2107 breaks down an image into seven smaller images of varying size, based
2110 libpng can fill out those images or it can give them to you "as is".
2111 If you want them filled out, there are two ways to do that. The one
2112 mentioned in the PNG specification is to expand each pixel to cover
2113 those pixels that have not been read yet (the "rectangle" method).
2114 This results in a blocky image for the first pass, which gradually
2115 smooths out as more pixels are read. The other method is the "sparkle"
2116 method, where pixels are drawn only in their final locations, with the
2117 rest of the image remaining whatever colors they were initialized to
2118 before the start of the read. The first method usually looks better,
2119 but tends to be slower, as there are more pixels to put in the rows.
2121 If you don't want libpng to handle the interlacing details, just call
2122 png_read_rows() seven times to read in all seven images. Each of the
2123 images is a valid image by itself, or they can all be combined on an
2124 8x8 grid to form a single image (although if you intend to combine them
2125 you would be far better off using the libpng interlace handling).
2127 The first pass will return an image 1/8 as wide as the entire image
2128 (every 8th column starting in column 0) and 1/8 as high as the original
2129 (every 8th row starting in row 0), the second will be 1/8 as wide
2130 (starting in column 4) and 1/8 as high (also starting in row 0). The
2131 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
2132 1/8 as high (every 8th row starting in row 4), and the fourth pass will
2133 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
2134 and every 4th row starting in row 0). The fifth pass will return an
2135 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
2136 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
2137 (starting in column 1 and row 0). The seventh and final pass will be as
2138 wide as the original, and 1/2 as high, containing all of the odd
2139 numbered scanlines. Phew!
2141 If you want libpng to expand the images, call this before calling
2142 png_start_read_image() or png_read_update_info():
2144 if (interlace_type == PNG_INTERLACE_ADAM7)
2146 = png_set_interlace_handling(png_ptr);
2148 This will return the number of passes needed. Currently, this
2149 is seven, but may change if another interlace type is added.
2150 This function can be called even if the file is not interlaced,
2151 where it will return one pass.
2153 If you are not going to display the image after each pass, but are
2154 going to wait until the entire image is read in, use the sparkle
2155 effect. This effect is faster and the end result of either method
2156 is exactly the same. If you are planning on displaying the image
2157 after each pass, the "rectangle" effect is generally considered the
2160 If you only want the "sparkle" effect, just call png_read_rows() as
2161 normal, with the third parameter NULL. Make sure you make pass over
2162 the image number_of_passes times, and you don't change the data in the
2163 rows between calls. You can change the locations of the data, just
2164 not the data. Each pass only writes the pixels appropriate for that
2165 pass, and assumes the data from previous passes is still valid.
2167 png_read_rows(png_ptr, row_pointers, NULL,
2170 If you only want the first effect (the rectangles), do the same as
2171 before except pass the row buffer in the third parameter, and leave
2172 the second parameter NULL.
2174 png_read_rows(png_ptr, NULL, row_pointers,
2177 .SS Finishing a sequential read
2179 After you are finished reading the image through the
2180 low-level interface, you can finish reading the file. If you are
2181 interested in comments or time, which may be stored either before or
2182 after the image data, you should pass the separate png_info struct if
2183 you want to keep the comments from before and after the image
2184 separate. If you are not interested, you can pass NULL.
2186 png_read_end(png_ptr, end_info);
2188 When you are done, you can free all memory allocated by libpng like this:
2190 png_destroy_read_struct(&png_ptr, &info_ptr,
2193 It is also possible to individually free the info_ptr members that
2194 point to libpng-allocated storage with the following function:
2196 png_free_data(png_ptr, info_ptr, mask, seq)
2197 mask - identifies data to be freed, a mask
2198 containing the bitwise OR of one or
2200 PNG_FREE_PLTE, PNG_FREE_TRNS,
2201 PNG_FREE_HIST, PNG_FREE_ICCP,
2202 PNG_FREE_PCAL, PNG_FREE_ROWS,
2203 PNG_FREE_SCAL, PNG_FREE_SPLT,
2204 PNG_FREE_TEXT, PNG_FREE_UNKN,
2205 or simply PNG_FREE_ALL
2206 seq - sequence number of item to be freed
2209 This function may be safely called when the relevant storage has
2210 already been freed, or has not yet been allocated, or was allocated
2211 by the user and not by libpng, and will in those cases do nothing.
2212 The "seq" parameter is ignored if only one item of the selected data
2213 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
2214 are allowed for the data type identified in the mask, such as text or
2215 sPLT, only the n'th item in the structure is freed, where n is "seq".
2217 The default behavior is only to free data that was allocated internally
2218 by libpng. This can be changed, so that libpng will not free the data,
2219 or so that it will free data that was allocated by the user with png_malloc()
2220 or png_zalloc() and passed in via a png_set_*() function, with
2222 png_data_freer(png_ptr, info_ptr, freer, mask)
2223 mask - which data elements are affected
2224 same choices as in png_free_data()
2226 PNG_DESTROY_WILL_FREE_DATA
2227 PNG_SET_WILL_FREE_DATA
2228 PNG_USER_WILL_FREE_DATA
2230 This function only affects data that has already been allocated.
2231 You can call this function after reading the PNG data but before calling
2232 any png_set_*() functions, to control whether the user or the png_set_*()
2233 function is responsible for freeing any existing data that might be present,
2234 and again after the png_set_*() functions to control whether the user
2235 or png_destroy_*() is supposed to free the data. When the user assumes
2236 responsibility for libpng-allocated data, the application must use
2237 png_free() to free it, and when the user transfers responsibility to libpng
2238 for data that the user has allocated, the user must have used png_malloc()
2239 or png_zalloc() to allocate it.
2241 If you allocated your row_pointers in a single block, as suggested above in
2242 the description of the high level read interface, you must not transfer
2243 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2244 because they would also try to free the individual row_pointers[i].
2246 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2247 separately, do not transfer responsibility for freeing text_ptr to libpng,
2248 because when libpng fills a png_text structure it combines these members with
2249 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2250 if you transfer responsibility for free'ing text_ptr from libpng to your
2251 application, your application must not separately free those members.
2253 The png_free_data() function will turn off the "valid" flag for anything
2254 it frees. If you need to turn the flag off for a chunk that was freed by
2255 your application instead of by libpng, you can use
2257 png_set_invalid(png_ptr, info_ptr, mask);
2258 mask - identifies the chunks to be made invalid,
2259 containing the bitwise OR of one or
2261 PNG_INFO_gAMA, PNG_INFO_sBIT,
2262 PNG_INFO_cHRM, PNG_INFO_PLTE,
2263 PNG_INFO_tRNS, PNG_INFO_bKGD,
2264 PNG_INFO_hIST, PNG_INFO_pHYs,
2265 PNG_INFO_oFFs, PNG_INFO_tIME,
2266 PNG_INFO_pCAL, PNG_INFO_sRGB,
2267 PNG_INFO_iCCP, PNG_INFO_sPLT,
2268 PNG_INFO_sCAL, PNG_INFO_IDAT
2270 For a more compact example of reading a PNG image, see the file example.c.
2272 .SS Reading PNG files progressively
2274 The progressive reader is slightly different then the non-progressive
2275 reader. Instead of calling png_read_info(), png_read_rows(), and
2276 png_read_end(), you make one call to png_process_data(), which calls
2277 callbacks when it has the info, a row, or the end of the image. You
2278 set up these callbacks with png_set_progressive_read_fn(). You don't
2279 have to worry about the input/output functions of libpng, as you are
2280 giving the library the data directly in png_process_data(). I will
2281 assume that you have read the section on reading PNG files above,
2282 so I will only highlight the differences (although I will show
2285 png_structp png_ptr;
2288 /* An example code fragment of how you would
2289 initialize the progressive reader in your
2292 initialize_png_reader()
2294 png_ptr = png_create_read_struct
2295 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2296 user_error_fn, user_warning_fn);
2299 info_ptr = png_create_info_struct(png_ptr);
2302 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2307 if (setjmp(png_jmpbuf(png_ptr)))
2309 png_destroy_read_struct(&png_ptr, &info_ptr,
2314 /* This one's new. You can provide functions
2315 to be called when the header info is valid,
2316 when each row is completed, and when the image
2317 is finished. If you aren't using all functions,
2318 you can specify NULL parameters. Even when all
2319 three functions are NULL, you need to call
2320 png_set_progressive_read_fn(). You can use
2321 any struct as the user_ptr (cast to a void pointer
2322 for the function call), and retrieve the pointer
2323 from inside the callbacks using the function
2325 png_get_progressive_ptr(png_ptr);
2327 which will return a void pointer, which you have
2328 to cast appropriately.
2330 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2331 info_callback, row_callback, end_callback);
2336 /* A code fragment that you call as you receive blocks
2339 process_data(png_bytep buffer, png_uint_32 length)
2341 if (setjmp(png_jmpbuf(png_ptr)))
2343 png_destroy_read_struct(&png_ptr, &info_ptr,
2348 /* This one's new also. Simply give it a chunk
2349 of data from the file stream (in order, of
2350 course). On machines with segmented memory
2351 models machines, don't give it any more than
2352 64K. The library seems to run fine with sizes
2353 of 4K. Although you can give it much less if
2354 necessary (I assume you can give it chunks of
2355 1 byte, I haven't tried less then 256 bytes
2356 yet). When this function returns, you may
2357 want to display any rows that were generated
2358 in the row callback if you don't already do
2361 png_process_data(png_ptr, info_ptr, buffer, length);
2365 /* This function is called (as set by
2366 png_set_progressive_read_fn() above) when enough data
2367 has been supplied so all of the header has been
2371 info_callback(png_structp png_ptr, png_infop info)
2373 /* Do any setup here, including setting any of
2374 the transformations mentioned in the Reading
2375 PNG files section. For now, you _must_ call
2376 either png_start_read_image() or
2377 png_read_update_info() after all the
2378 transformations are set (even if you don't set
2379 any). You may start getting rows before
2380 png_process_data() returns, so this is your
2381 last chance to prepare for that.
2385 /* This function is called when each row of image
2388 row_callback(png_structp png_ptr, png_bytep new_row,
2389 png_uint_32 row_num, int pass)
2391 /* If the image is interlaced, and you turned
2392 on the interlace handler, this function will
2393 be called for every row in every pass. Some
2394 of these rows will not be changed from the
2395 previous pass. When the row is not changed,
2396 the new_row variable will be NULL. The rows
2397 and passes are called in order, so you don't
2398 really need the row_num and pass, but I'm
2399 supplying them because it may make your life
2402 For the non-NULL rows of interlaced images,
2403 you must call png_progressive_combine_row()
2404 passing in the row and the old row. You can
2405 call this function for NULL rows (it will just
2406 return) and for non-interlaced images (it just
2407 does the memcpy for you) if it will make the
2408 code easier. Thus, you can just do this for
2412 png_progressive_combine_row(png_ptr, old_row,
2415 /* where old_row is what was displayed for
2416 previously for the row. Note that the first
2417 pass (pass == 0, really) will completely cover
2418 the old row, so the rows do not have to be
2419 initialized. After the first pass (and only
2420 for interlaced images), you will have to pass
2421 the current row, and the function will combine
2422 the old row and the new row.
2427 end_callback(png_structp png_ptr, png_infop info)
2429 /* This function is called after the whole image
2430 has been read, including any chunks after the
2431 image (up to and including the IEND). You
2432 will usually have the same info chunk as you
2433 had in the header, although some data may have
2434 been added to the comments and time fields.
2436 Most people won't do much here, perhaps setting
2437 a flag that marks the image as finished.
2445 Much of this is very similar to reading. However, everything of
2446 importance is repeated here, so you won't have to constantly look
2447 back up in the reading section to understand writing.
2451 You will want to do the I/O initialization before you get into libpng,
2452 so if it doesn't work, you don't have anything to undo. If you are not
2453 using the standard I/O functions, you will need to replace them with
2454 custom writing functions. See the discussion under Customizing libpng.
2456 FILE *fp = fopen(file_name, "wb");
2462 Next, png_struct and png_info need to be allocated and initialized.
2463 As these can be both relatively large, you may not want to store these
2464 on the stack, unless you have stack space to spare. Of course, you
2465 will want to check if they return NULL. If you are also reading,
2466 you won't want to name your read structure and your write structure
2467 both "png_ptr"; you can call them anything you like, such as
2468 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2470 png_structp png_ptr = png_create_write_struct
2471 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2472 user_error_fn, user_warning_fn);
2476 png_infop info_ptr = png_create_info_struct(png_ptr);
2479 png_destroy_write_struct(&png_ptr,
2484 If you want to use your own memory allocation routines,
2485 define PNG_USER_MEM_SUPPORTED and use
2486 png_create_write_struct_2() instead of png_create_write_struct():
2488 png_structp png_ptr = png_create_write_struct_2
2489 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2490 user_error_fn, user_warning_fn, (png_voidp)
2491 user_mem_ptr, user_malloc_fn, user_free_fn);
2493 After you have these structures, you will need to set up the
2494 error handling. When libpng encounters an error, it expects to
2495 longjmp() back to your routine. Therefore, you will need to call
2496 setjmp() and pass the png_jmpbuf(png_ptr). If you
2497 write the file from different routines, you will need to update
2498 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2499 call a png_*() function. See your documentation of setjmp/longjmp
2500 for your compiler for more information on setjmp/longjmp. See
2501 the discussion on libpng error handling in the Customizing Libpng
2502 section below for more information on the libpng error handling.
2504 if (setjmp(png_jmpbuf(png_ptr)))
2506 png_destroy_write_struct(&png_ptr, &info_ptr);
2513 If you would rather avoid the complexity of setjmp/longjmp issues,
2514 you can compile libpng with PNG_NO_SETJMP, in which case
2515 errors will result in a call to PNG_ABORT() which defaults to abort().
2517 You can #define PNG_ABORT() to a function that does something
2518 more useful than abort(), as long as your function does not
2521 Now you need to set up the output code. The default for libpng is to
2522 use the C function fwrite(). If you use this, you will need to pass a
2523 valid FILE * in the function png_init_io(). Be sure that the file is
2524 opened in binary mode. Again, if you wish to handle writing data in
2525 another way, see the discussion on libpng I/O handling in the Customizing
2526 Libpng section below.
2528 png_init_io(png_ptr, fp);
2530 If you are embedding your PNG into a datastream such as MNG, and don't
2531 want libpng to write the 8-byte signature, or if you have already
2532 written the signature in your application, use
2534 png_set_sig_bytes(png_ptr, 8);
2536 to inform libpng that it should not write a signature.
2540 At this point, you can set up a callback function that will be
2541 called after each row has been written, which you can use to control
2542 a progress meter or the like. It's demonstrated in pngtest.c.
2543 You must supply a function
2545 void write_row_callback(png_ptr, png_uint_32 row,
2548 /* put your code here */
2551 (You can give it another name that you like instead of "write_row_callback")
2553 To inform libpng about your function, use
2555 png_set_write_status_fn(png_ptr, write_row_callback);
2557 You now have the option of modifying how the compression library will
2558 run. The following functions are mainly for testing, but may be useful
2559 in some cases, like if you need to write PNG files extremely fast and
2560 are willing to give up some compression, or if you want to get the
2561 maximum possible compression at the expense of slower writing. If you
2562 have no special needs in this area, let the library do what it wants by
2563 not calling this function at all, as it has been tuned to deliver a good
2564 speed/compression ratio. The second parameter to png_set_filter() is
2565 the filter method, for which the only valid values are 0 (as of the
2566 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2567 a PNG datastream that is to be embedded in a MNG datastream). The third
2568 parameter is a flag that indicates which filter type(s) are to be tested
2569 for each scanline. See the PNG specification for details on the specific
2573 /* turn on or off filtering, and/or choose
2574 specific filters. You can use either a single
2575 PNG_FILTER_VALUE_NAME or the bitwise OR of one
2576 or more PNG_FILTER_NAME masks. */
2577 png_set_filter(png_ptr, 0,
2578 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2579 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2580 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2581 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
2582 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2586 wants to start and stop using particular filters during compression,
2587 it should start out with all of the filters (to ensure that the previous
2588 row of pixels will be stored in case it's needed later), and then add
2589 and remove them after the start of compression.
2591 If you are writing a PNG datastream that is to be embedded in a MNG
2592 datastream, the second parameter can be either 0 or 64.
2594 The png_set_compression_*() functions interface to the zlib compression
2595 library, and should mostly be ignored unless you really know what you are
2596 doing. The only generally useful call is png_set_compression_level()
2597 which changes how much time zlib spends on trying to compress the image
2598 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2599 with zlib) for details on the compression levels.
2601 /* set the zlib compression level */
2602 png_set_compression_level(png_ptr,
2603 Z_BEST_COMPRESSION);
2605 /* set other zlib parameters */
2606 png_set_compression_mem_level(png_ptr, 8);
2607 png_set_compression_strategy(png_ptr,
2608 Z_DEFAULT_STRATEGY);
2609 png_set_compression_window_bits(png_ptr, 15);
2610 png_set_compression_method(png_ptr, 8);
2611 png_set_compression_buffer_size(png_ptr, 8192)
2613 extern PNG_EXPORT(void,png_set_zbuf_size)
2615 .SS Setting the contents of info for output
2617 You now need to fill in the png_info structure with all the data you
2618 wish to write before the actual image. Note that the only thing you
2619 are allowed to write after the image is the text chunks and the time
2620 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2621 the latest PNG specification for more information on that. If you
2622 wish to write them before the image, fill them in now, and flag that
2623 data as being valid. If you want to wait until after the data, don't
2624 fill them until png_write_end(). For all the fields in png_info and
2625 their data types, see png.h. For explanations of what the fields
2626 contain, see the PNG specification.
2628 Some of the more important parts of the png_info are:
2630 png_set_IHDR(png_ptr, info_ptr, width, height,
2631 bit_depth, color_type, interlace_type,
2632 compression_type, filter_method)
2633 width - holds the width of the image
2634 in pixels (up to 2^31).
2635 height - holds the height of the image
2636 in pixels (up to 2^31).
2637 bit_depth - holds the bit depth of one of the
2639 (valid values are 1, 2, 4, 8, 16
2640 and depend also on the
2641 color_type. See also significant
2643 color_type - describes which color/alpha
2644 channels are present.
2646 (bit depths 1, 2, 4, 8, 16)
2647 PNG_COLOR_TYPE_GRAY_ALPHA
2649 PNG_COLOR_TYPE_PALETTE
2650 (bit depths 1, 2, 4, 8)
2653 PNG_COLOR_TYPE_RGB_ALPHA
2656 PNG_COLOR_MASK_PALETTE
2657 PNG_COLOR_MASK_COLOR
2658 PNG_COLOR_MASK_ALPHA
2660 interlace_type - PNG_INTERLACE_NONE or
2662 compression_type - (must be
2663 PNG_COMPRESSION_TYPE_DEFAULT)
2664 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2665 or, if you are writing a PNG to
2666 be embedded in a MNG datastream,
2668 PNG_INTRAPIXEL_DIFFERENCING)
2670 If you call png_set_IHDR(), the call must appear before any of the
2671 other png_set_*() functions, because they might require access to some of
2672 the IHDR settings. The remaining png_set_*() functions can be called
2675 If you wish, you can reset the compression_type, interlace_type, or
2676 filter_method later by calling png_set_IHDR() again; if you do this, the
2677 width, height, bit_depth, and color_type must be the same in each call.
2679 png_set_PLTE(png_ptr, info_ptr, palette,
2681 palette - the palette for the file
2682 (array of png_color)
2683 num_palette - number of entries in the palette
2685 png_set_gAMA(png_ptr, info_ptr, gamma);
2686 gamma - the gamma the image was created
2689 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2690 srgb_intent - the rendering intent
2691 (PNG_INFO_sRGB) The presence of
2692 the sRGB chunk means that the pixel
2693 data is in the sRGB color space.
2694 This chunk also implies specific
2695 values of gAMA and cHRM. Rendering
2696 intent is the CSS-1 property that
2697 has been defined by the International
2699 (http://www.color.org).
2701 PNG_sRGB_INTENT_SATURATION,
2702 PNG_sRGB_INTENT_PERCEPTUAL,
2703 PNG_sRGB_INTENT_ABSOLUTE, or
2704 PNG_sRGB_INTENT_RELATIVE.
2707 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2709 srgb_intent - the rendering intent
2710 (PNG_INFO_sRGB) The presence of the
2711 sRGB chunk means that the pixel
2712 data is in the sRGB color space.
2713 This function also causes gAMA and
2714 cHRM chunks with the specific values
2715 that are consistent with sRGB to be
2718 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2720 name - The profile name.
2721 compression - The compression type; always
2722 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2723 You may give NULL to this argument to
2725 profile - International Color Consortium color
2726 profile data. May contain NULs.
2727 proflen - length of profile data in bytes.
2729 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2730 sig_bit - the number of significant bits for
2731 (PNG_INFO_sBIT) each of the gray, red,
2732 green, and blue channels, whichever are
2733 appropriate for the given color type
2736 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
2737 num_trans, trans_color);
2738 trans_alpha - array of alpha (transparency)
2739 entries for palette (PNG_INFO_tRNS)
2740 trans_color - graylevel or color sample values
2741 (in order red, green, blue) of the
2742 single transparent color for
2743 non-paletted images (PNG_INFO_tRNS)
2744 num_trans - number of transparent entries
2747 png_set_hIST(png_ptr, info_ptr, hist);
2749 hist - histogram of palette (array of
2752 png_set_tIME(png_ptr, info_ptr, mod_time);
2753 mod_time - time image was last modified
2756 png_set_bKGD(png_ptr, info_ptr, background);
2757 background - background color (PNG_VALID_bKGD)
2759 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2760 text_ptr - array of png_text holding image
2762 text_ptr[i].compression - type of compression used
2763 on "text" PNG_TEXT_COMPRESSION_NONE
2764 PNG_TEXT_COMPRESSION_zTXt
2765 PNG_ITXT_COMPRESSION_NONE
2766 PNG_ITXT_COMPRESSION_zTXt
2767 text_ptr[i].key - keyword for comment. Must contain
2769 text_ptr[i].text - text comments for current
2770 keyword. Can be NULL or empty.
2771 text_ptr[i].text_length - length of text string,
2772 after decompression, 0 for iTXt
2773 text_ptr[i].itxt_length - length of itxt string,
2774 after decompression, 0 for tEXt/zTXt
2775 text_ptr[i].lang - language of comment (NULL or
2777 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2778 or empty for unknown).
2779 Note that the itxt_length, lang, and lang_key
2780 members of the text_ptr structure only exist
2781 when the library is built with iTXt chunk support.
2783 num_text - number of comments
2785 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2787 palette_ptr - array of png_sPLT_struct structures
2788 to be added to the list of palettes
2789 in the info structure.
2790 num_spalettes - number of palette structures to be
2793 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2795 offset_x - positive offset from the left
2797 offset_y - positive offset from the top
2799 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2801 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2803 res_x - pixels/unit physical resolution
2805 res_y - pixels/unit physical resolution
2807 unit_type - PNG_RESOLUTION_UNKNOWN,
2808 PNG_RESOLUTION_METER
2810 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2811 unit - physical scale units (an integer)
2812 width - width of a pixel in physical scale units
2813 height - height of a pixel in physical scale units
2814 (width and height are doubles)
2816 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2817 unit - physical scale units (an integer)
2818 width - width of a pixel in physical scale units
2819 height - height of a pixel in physical scale units
2820 (width and height are strings like "2.54")
2822 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2824 unknowns - array of png_unknown_chunk
2825 structures holding unknown chunks
2826 unknowns[i].name - name of unknown chunk
2827 unknowns[i].data - data of unknown chunk
2828 unknowns[i].size - size of unknown chunk's data
2829 unknowns[i].location - position to write chunk in file
2830 0: do not write chunk
2831 PNG_HAVE_IHDR: before PLTE
2832 PNG_HAVE_PLTE: before IDAT
2833 PNG_AFTER_IDAT: after IDAT
2835 The "location" member is set automatically according to
2836 what part of the output file has already been written.
2837 You can change its value after calling png_set_unknown_chunks()
2838 as demonstrated in pngtest.c. Within each of the "locations",
2839 the chunks are sequenced according to their position in the
2840 structure (that is, the value of "i", which is the order in which
2841 the chunk was either read from the input file or defined with
2842 png_set_unknown_chunks).
2844 A quick word about text and num_text. text is an array of png_text
2845 structures. num_text is the number of valid structures in the array.
2846 Each png_text structure holds a language code, a keyword, a text value,
2847 and a compression type.
2849 The compression types have the same valid numbers as the compression
2850 types of the image data. Currently, the only valid number is zero.
2851 However, you can store text either compressed or uncompressed, unlike
2852 images, which always have to be compressed. So if you don't want the
2853 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2854 Because tEXt and zTXt chunks don't have a language field, if you
2855 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2856 any language code or translated keyword will not be written out.
2858 Until text gets around 1000 bytes, it is not worth compressing it.
2859 After the text has been written out to the file, the compression type
2860 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2861 so that it isn't written out again at the end (in case you are calling
2862 png_write_end() with the same struct.
2864 The keywords that are given in the PNG Specification are:
2866 Title Short (one line) title or
2868 Author Name of image's creator
2869 Description Description of image (possibly long)
2870 Copyright Copyright notice
2871 Creation Time Time of original image creation
2872 (usually RFC 1123 format, see below)
2873 Software Software used to create the image
2874 Disclaimer Legal disclaimer
2875 Warning Warning of nature of content
2876 Source Device used to create the image
2877 Comment Miscellaneous comment; conversion
2878 from other image format
2880 The keyword-text pairs work like this. Keywords should be short
2881 simple descriptions of what the comment is about. Some typical
2882 keywords are found in the PNG specification, as is some recommendations
2883 on keywords. You can repeat keywords in a file. You can even write
2884 some text before the image and some after. For example, you may want
2885 to put a description of the image before the image, but leave the
2886 disclaimer until after, so viewers working over modem connections
2887 don't have to wait for the disclaimer to go over the modem before
2888 they start seeing the image. Finally, keywords should be full
2889 words, not abbreviations. Keywords and text are in the ISO 8859-1
2890 (Latin-1) character set (a superset of regular ASCII) and can not
2891 contain NUL characters, and should not contain control or other
2892 unprintable characters. To make the comments widely readable, stick
2893 with basic ASCII, and avoid machine specific character set extensions
2894 like the IBM-PC character set. The keyword must be present, but
2895 you can leave off the text string on non-compressed pairs.
2896 Compressed pairs must have a text string, as only the text string
2897 is compressed anyway, so the compression would be meaningless.
2899 PNG supports modification time via the png_time structure. Two
2900 conversion routines are provided, png_convert_from_time_t() for
2901 time_t and png_convert_from_struct_tm() for struct tm. The
2902 time_t routine uses gmtime(). You don't have to use either of
2903 these, but if you wish to fill in the png_time structure directly,
2904 you should provide the time in universal time (GMT) if possible
2905 instead of your local time. Note that the year number is the full
2906 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2907 that months start with 1.
2909 If you want to store the time of the original image creation, you should
2910 use a plain tEXt chunk with the "Creation Time" keyword. This is
2911 necessary because the "creation time" of a PNG image is somewhat vague,
2912 depending on whether you mean the PNG file, the time the image was
2913 created in a non-PNG format, a still photo from which the image was
2914 scanned, or possibly the subject matter itself. In order to facilitate
2915 machine-readable dates, it is recommended that the "Creation Time"
2916 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2917 although this isn't a requirement. Unlike the tIME chunk, the
2918 "Creation Time" tEXt chunk is not expected to be automatically changed
2919 by the software. To facilitate the use of RFC 1123 dates, a function
2920 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2921 time to an RFC 1123 format string.
2923 .SS Writing unknown chunks
2925 You can use the png_set_unknown_chunks function to queue up chunks
2926 for writing. You give it a chunk name, raw data, and a size; that's
2927 all there is to it. The chunks will be written by the next following
2928 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2929 Any chunks previously read into the info structure's unknown-chunk
2930 list will also be written out in a sequence that satisfies the PNG
2931 specification's ordering rules.
2933 .SS The high-level write interface
2935 At this point there are two ways to proceed; through the high-level
2936 write interface, or through a sequence of low-level write operations.
2937 You can use the high-level interface if your image data is present
2938 in the info structure. All defined output
2939 transformations are permitted, enabled by the following masks.
2941 PNG_TRANSFORM_IDENTITY No transformation
2942 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2943 PNG_TRANSFORM_PACKSWAP Change order of packed
2945 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2946 PNG_TRANSFORM_SHIFT Normalize pixels to the
2948 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2950 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2952 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2954 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2955 PNG_TRANSFORM_STRIP_FILLER Strip out filler
2957 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
2959 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
2962 If you have valid image data in the info structure (you can use
2963 png_set_rows() to put image data in the info structure), simply do this:
2965 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2967 where png_transforms is an integer containing the bitwise OR of some set of
2968 transformation flags. This call is equivalent to png_write_info(),
2969 followed the set of transformations indicated by the transform mask,
2970 then png_write_image(), and finally png_write_end().
2972 (The final parameter of this call is not yet used. Someday it might point
2973 to transformation parameters required by some future output transform.)
2975 You must use png_transforms and not call any png_set_transform() functions
2976 when you use png_write_png().
2978 .SS The low-level write interface
2980 If you are going the low-level route instead, you are now ready to
2981 write all the file information up to the actual image data. You do
2982 this with a call to png_write_info().
2984 png_write_info(png_ptr, info_ptr);
2986 Note that there is one transformation you may need to do before
2987 png_write_info(). In PNG files, the alpha channel in an image is the
2988 level of opacity. If your data is supplied as a level of transparency,
2989 you can invert the alpha channel before you write it, so that 0 is
2990 fully transparent and 255 (in 8-bit or paletted images) or 65535
2991 (in 16-bit images) is fully opaque, with
2993 png_set_invert_alpha(png_ptr);
2995 This must appear before png_write_info() instead of later with the
2996 other transformations because in the case of paletted images the tRNS
2997 chunk data has to be inverted before the tRNS chunk is written. If
2998 your image is not a paletted image, the tRNS data (which in such cases
2999 represents a single color to be rendered as transparent) won't need to
3000 be changed, and you can safely do this transformation after your
3001 png_write_info() call.
3003 If you need to write a private chunk that you want to appear before
3004 the PLTE chunk when PLTE is present, you can write the PNG info in
3005 two steps, and insert code to write your own chunk between them:
3007 png_write_info_before_PLTE(png_ptr, info_ptr);
3008 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3009 png_write_info(png_ptr, info_ptr);
3011 After you've written the file information, you can set up the library
3012 to handle any special transformations of the image data. The various
3013 ways to transform the data will be described in the order that they
3014 should occur. This is important, as some of these change the color
3015 type and/or bit depth of the data, and some others only work on
3016 certain color types and bit depths. Even though each transformation
3017 checks to see if it has data that it can do something with, you should
3018 make sure to only enable a transformation if it will be valid for the
3019 data. For example, don't swap red and blue on grayscale data.
3021 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3022 the library to strip input data that has 4 or 8 bytes per pixel down
3023 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3026 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3028 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3029 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3030 is stored XRGB or RGBX.
3032 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3033 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3034 If the data is supplied at 1 pixel per byte, use this code, which will
3035 correctly pack the pixels into a single byte:
3037 png_set_packing(png_ptr);
3039 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3040 data is of another bit depth, you can write an sBIT chunk into the
3041 file so that decoders can recover the original data if desired.
3043 /* Set the true bit depth of the image data */
3044 if (color_type & PNG_COLOR_MASK_COLOR)
3046 sig_bit.red = true_bit_depth;
3047 sig_bit.green = true_bit_depth;
3048 sig_bit.blue = true_bit_depth;
3052 sig_bit.gray = true_bit_depth;
3054 if (color_type & PNG_COLOR_MASK_ALPHA)
3056 sig_bit.alpha = true_bit_depth;
3059 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3061 If the data is stored in the row buffer in a bit depth other than
3062 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3063 this will scale the values to appear to be the correct bit depth as
3066 png_set_shift(png_ptr, &sig_bit);
3068 PNG files store 16 bit pixels in network byte order (big-endian,
3069 ie. most significant bits first). This code would be used if they are
3070 supplied the other way (little-endian, i.e. least significant bits
3071 first, the way PCs store them):
3074 png_set_swap(png_ptr);
3076 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3077 need to change the order the pixels are packed into bytes, you can use:
3080 png_set_packswap(png_ptr);
3082 PNG files store 3 color pixels in red, green, blue order. This code
3083 would be used if they are supplied as blue, green, red:
3085 png_set_bgr(png_ptr);
3087 PNG files describe monochrome as black being zero and white being
3088 one. This code would be used if the pixels are supplied with this reversed
3089 (black being one and white being zero):
3091 png_set_invert_mono(png_ptr);
3093 Finally, you can write your own transformation function if none of
3094 the existing ones meets your needs. This is done by setting a callback
3097 png_set_write_user_transform_fn(png_ptr,
3098 write_transform_fn);
3100 You must supply the function
3102 void write_transform_fn(png_ptr ptr, row_info_ptr
3103 row_info, png_bytep data)
3105 See pngtest.c for a working example. Your function will be called
3106 before any of the other transformations are processed.
3108 You can also set up a pointer to a user structure for use by your
3111 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3113 The user_channels and user_depth parameters of this function are ignored
3114 when writing; you can set them to zero as shown.
3116 You can retrieve the pointer via the function png_get_user_transform_ptr().
3119 voidp write_user_transform_ptr =
3120 png_get_user_transform_ptr(png_ptr);
3122 It is possible to have libpng flush any pending output, either manually,
3123 or automatically after a certain number of lines have been written. To
3124 flush the output stream a single time call:
3126 png_write_flush(png_ptr);
3128 and to have libpng flush the output stream periodically after a certain
3129 number of scanlines have been written, call:
3131 png_set_flush(png_ptr, nrows);
3133 Note that the distance between rows is from the last time png_write_flush()
3134 was called, or the first row of the image if it has never been called.
3135 So if you write 50 lines, and then png_set_flush 25, it will flush the
3136 output on the next scanline, and every 25 lines thereafter, unless
3137 png_write_flush() is called before 25 more lines have been written.
3138 If nrows is too small (less than about 10 lines for a 640 pixel wide
3139 RGB image) the image compression may decrease noticeably (although this
3140 may be acceptable for real-time applications). Infrequent flushing will
3141 only degrade the compression performance by a few percent over images
3142 that do not use flushing.
3144 .SS Writing the image data
3146 That's it for the transformations. Now you can write the image data.
3147 The simplest way to do this is in one function call. If you have the
3148 whole image in memory, you can just call png_write_image() and libpng
3149 will write the image. You will need to pass in an array of pointers to
3150 each row. This function automatically handles interlacing, so you don't
3151 need to call png_set_interlace_handling() or call this function multiple
3152 times, or any of that other stuff necessary with png_write_rows().
3154 png_write_image(png_ptr, row_pointers);
3156 where row_pointers is:
3158 png_byte *row_pointers[height];
3160 You can point to void or char or whatever you use for pixels.
3162 If you don't want to write the whole image at once, you can
3163 use png_write_rows() instead. If the file is not interlaced,
3166 png_write_rows(png_ptr, row_pointers,
3169 row_pointers is the same as in the png_write_image() call.
3171 If you are just writing one row at a time, you can do this with
3172 a single row_pointer instead of an array of row_pointers:
3174 png_bytep row_pointer = row;
3176 png_write_row(png_ptr, row_pointer);
3178 When the file is interlaced, things can get a good deal more complicated.
3179 The only currently (as of the PNG Specification version 1.2, dated July
3180 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
3181 scheme, that breaks down an image into seven smaller images of varying
3182 size. libpng will build these images for you, or you can do them
3183 yourself. If you want to build them yourself, see the PNG specification
3184 for details of which pixels to write when.
3186 If you don't want libpng to handle the interlacing details, just
3187 use png_set_interlace_handling() and call png_write_rows() the
3188 correct number of times to write all seven sub-images.
3190 If you want libpng to build the sub-images, call this before you start
3194 png_set_interlace_handling(png_ptr);
3196 This will return the number of passes needed. Currently, this is seven,
3197 but may change if another interlace type is added.
3199 Then write the complete image number_of_passes times.
3201 png_write_rows(png_ptr, row_pointers,
3204 As some of these rows are not used, and thus return immediately, you may
3205 want to read about interlacing in the PNG specification, and only update
3206 the rows that are actually used.
3208 .SS Finishing a sequential write
3210 After you are finished writing the image, you should finish writing
3211 the file. If you are interested in writing comments or time, you should
3212 pass an appropriately filled png_info pointer. If you are not interested,
3215 png_write_end(png_ptr, info_ptr);
3217 When you are done, you can free all memory used by libpng like this:
3219 png_destroy_write_struct(&png_ptr, &info_ptr);
3221 It is also possible to individually free the info_ptr members that
3222 point to libpng-allocated storage with the following function:
3224 png_free_data(png_ptr, info_ptr, mask, seq)
3225 mask - identifies data to be freed, a mask
3226 containing the bitwise OR of one or
3228 PNG_FREE_PLTE, PNG_FREE_TRNS,
3229 PNG_FREE_HIST, PNG_FREE_ICCP,
3230 PNG_FREE_PCAL, PNG_FREE_ROWS,
3231 PNG_FREE_SCAL, PNG_FREE_SPLT,
3232 PNG_FREE_TEXT, PNG_FREE_UNKN,
3233 or simply PNG_FREE_ALL
3234 seq - sequence number of item to be freed
3237 This function may be safely called when the relevant storage has
3238 already been freed, or has not yet been allocated, or was allocated
3239 by the user and not by libpng, and will in those cases do nothing.
3240 The "seq" parameter is ignored if only one item of the selected data
3241 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3242 are allowed for the data type identified in the mask, such as text or
3243 sPLT, only the n'th item in the structure is freed, where n is "seq".
3245 If you allocated data such as a palette that you passed in to libpng
3246 with png_set_*, you must not free it until just before the call to
3247 png_destroy_write_struct().
3249 The default behavior is only to free data that was allocated internally
3250 by libpng. This can be changed, so that libpng will not free the data,
3251 or so that it will free data that was allocated by the user with png_malloc()
3252 or png_zalloc() and passed in via a png_set_*() function, with
3254 png_data_freer(png_ptr, info_ptr, freer, mask)
3255 mask - which data elements are affected
3256 same choices as in png_free_data()
3258 PNG_DESTROY_WILL_FREE_DATA
3259 PNG_SET_WILL_FREE_DATA
3260 PNG_USER_WILL_FREE_DATA
3262 For example, to transfer responsibility for some data from a read structure
3263 to a write structure, you could use
3265 png_data_freer(read_ptr, read_info_ptr,
3266 PNG_USER_WILL_FREE_DATA,
3267 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3268 png_data_freer(write_ptr, write_info_ptr,
3269 PNG_DESTROY_WILL_FREE_DATA,
3270 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3272 thereby briefly reassigning responsibility for freeing to the user but
3273 immediately afterwards reassigning it once more to the write_destroy
3274 function. Having done this, it would then be safe to destroy the read
3275 structure and continue to use the PLTE, tRNS, and hIST data in the write
3278 This function only affects data that has already been allocated.
3279 You can call this function before calling after the png_set_*() functions
3280 to control whether the user or png_destroy_*() is supposed to free the data.
3281 When the user assumes responsibility for libpng-allocated data, the
3282 application must use
3283 png_free() to free it, and when the user transfers responsibility to libpng
3284 for data that the user has allocated, the user must have used png_malloc()
3285 or png_zalloc() to allocate it.
3287 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3288 separately, do not transfer responsibility for freeing text_ptr to libpng,
3289 because when libpng fills a png_text structure it combines these members with
3290 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3291 if you transfer responsibility for free'ing text_ptr from libpng to your
3292 application, your application must not separately free those members.
3293 For a more compact example of writing a PNG image, see the file example.c.
3295 .SH V. Modifying/Customizing libpng:
3297 There are two issues here. The first is changing how libpng does
3298 standard things like memory allocation, input/output, and error handling.
3299 The second deals with more complicated things like adding new chunks,
3300 adding new transformations, and generally changing how libpng works.
3301 Both of those are compile-time issues; that is, they are generally
3302 determined at the time the code is written, and there is rarely a need
3303 to provide the user with a means of changing them.
3305 Memory allocation, input/output, and error handling
3307 All of the memory allocation, input/output, and error handling in libpng
3308 goes through callbacks that are user-settable. The default routines are
3309 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3310 these functions, call the appropriate png_set_*_fn() function.
3312 Memory allocation is done through the functions png_malloc(), png_calloc(),
3313 and png_free(). These currently just call the standard C functions.
3314 png_calloc() calls png_malloc() and then png_memset() to clear the newly
3315 allocated memory to zero. If your pointers can't access more then 64K
3316 at a time, you will want to set MAXSEG_64K in zlib.h. Since it is
3317 unlikely that the method of handling memory allocation on a platform
3318 will change between applications, these functions must be modified in
3319 the library at compile time. If you prefer to use a different method
3320 of allocating and freeing data, you can use png_create_read_struct_2() or
3321 png_create_write_struct_2() to register your own functions as described
3322 above. These functions also provide a void pointer that can be retrieved
3325 mem_ptr=png_get_mem_ptr(png_ptr);
3327 Your replacement memory functions must have prototypes as follows:
3329 png_voidp malloc_fn(png_structp png_ptr,
3330 png_alloc_size_t size);
3331 void free_fn(png_structp png_ptr, png_voidp ptr);
3333 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3334 function will normally call png_error() if it receives a NULL from the
3335 system memory allocator or from your replacement malloc_fn().
3337 Your free_fn() will never be called with a NULL ptr, since libpng's
3338 png_free() checks for NULL before calling free_fn().
3340 Input/Output in libpng is done through png_read() and png_write(),
3341 which currently just call fread() and fwrite(). The FILE * is stored in
3342 png_struct and is initialized via png_init_io(). If you wish to change
3343 the method of I/O, the library supplies callbacks that you can set
3344 through the function png_set_read_fn() and png_set_write_fn() at run
3345 time, instead of calling the png_init_io() function. These functions
3346 also provide a void pointer that can be retrieved via the function
3347 png_get_io_ptr(). For example:
3349 png_set_read_fn(png_structp read_ptr,
3350 voidp read_io_ptr, png_rw_ptr read_data_fn)
3352 png_set_write_fn(png_structp write_ptr,
3353 voidp write_io_ptr, png_rw_ptr write_data_fn,
3354 png_flush_ptr output_flush_fn);
3356 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3357 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3359 The replacement I/O functions must have prototypes as follows:
3361 void user_read_data(png_structp png_ptr,
3362 png_bytep data, png_size_t length);
3363 void user_write_data(png_structp png_ptr,
3364 png_bytep data, png_size_t length);
3365 void user_flush_data(png_structp png_ptr);
3367 The user_read_data() function is responsible for detecting and
3368 handling end-of-data errors.
3370 Supplying NULL for the read, write, or flush functions sets them back
3371 to using the default C stream functions, which expect the io_ptr to
3372 point to a standard *FILE structure. It is probably a mistake
3373 to use NULL for one of write_data_fn and output_flush_fn but not both
3374 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
3375 It is an error to read from a write stream, and vice versa.
3377 Error handling in libpng is done through png_error() and png_warning().
3378 Errors handled through png_error() are fatal, meaning that png_error()
3379 should never return to its caller. Currently, this is handled via
3380 setjmp() and longjmp() (unless you have compiled libpng with
3381 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
3382 but you could change this to do things like exit() if you should wish,
3383 as long as your function does not return.
3385 On non-fatal errors, png_warning() is called
3386 to print a warning message, and then control returns to the calling code.
3387 By default png_error() and png_warning() print a message on stderr via
3388 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3389 (because you don't want the messages) or PNG_NO_STDIO defined (because
3390 fprintf() isn't available). If you wish to change the behavior of the error
3391 functions, you will need to set up your own message callbacks. These
3392 functions are normally supplied at the time that the png_struct is created.
3393 It is also possible to redirect errors and warnings to your own replacement
3394 functions after png_create_*_struct() has been called by calling:
3396 png_set_error_fn(png_structp png_ptr,
3397 png_voidp error_ptr, png_error_ptr error_fn,
3398 png_error_ptr warning_fn);
3400 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3402 If NULL is supplied for either error_fn or warning_fn, then the libpng
3403 default function will be used, calling fprintf() and/or longjmp() if a
3404 problem is encountered. The replacement error functions should have
3405 parameters as follows:
3407 void user_error_fn(png_structp png_ptr,
3408 png_const_charp error_msg);
3409 void user_warning_fn(png_structp png_ptr,
3410 png_const_charp warning_msg);
3412 The motivation behind using setjmp() and longjmp() is the C++ throw and
3413 catch exception handling methods. This makes the code much easier to write,
3414 as there is no need to check every return code of every function call.
3415 However, there are some uncertainties about the status of local variables
3416 after a longjmp, so the user may want to be careful about doing anything
3417 after setjmp returns non-zero besides returning itself. Consult your
3418 compiler documentation for more details. For an alternative approach, you
3419 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3423 If you need to read or write custom chunks, you may need to get deeper
3424 into the libpng code. The library now has mechanisms for storing
3425 and writing chunks of unknown type; you can even declare callbacks
3426 for custom chunks. However, this may not be good enough if the
3427 library code itself needs to know about interactions between your
3428 chunk and existing `intrinsic' chunks.
3430 If you need to write a new intrinsic chunk, first read the PNG
3431 specification. Acquire a first level of understanding of how it works.
3432 Pay particular attention to the sections that describe chunk names,
3433 and look at how other chunks were designed, so you can do things
3434 similarly. Second, check out the sections of libpng that read and
3435 write chunks. Try to find a chunk that is similar to yours and use
3436 it as a template. More details can be found in the comments inside
3437 the code. It is best to handle unknown chunks in a generic method,
3438 via callback functions, instead of by modifying libpng functions.
3440 If you wish to write your own transformation for the data, look through
3441 the part of the code that does the transformations, and check out some of
3442 the simpler ones to get an idea of how they work. Try to find a similar
3443 transformation to the one you want to add and copy off of it. More details
3444 can be found in the comments inside the code itself.
3446 .SS Configuring for 16 bit platforms
3448 You will want to look into zconf.h to tell zlib (and thus libpng) that
3449 it cannot allocate more then 64K at a time. Even if you can, the memory
3450 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3452 .SS Configuring for DOS
3454 For DOS users who only have access to the lower 640K, you will
3455 have to limit zlib's memory usage via a png_set_compression_mem_level()
3456 call. See zlib.h or zconf.h in the zlib library for more information.
3458 .SS Configuring for Medium Model
3460 Libpng's support for medium model has been tested on most of the popular
3461 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3462 defined, and FAR gets defined to far in pngconf.h, and you should be
3463 all set. Everything in the library (except for zlib's structure) is
3464 expecting far data. You must use the typedefs with the p or pp on
3465 the end for pointers (or at least look at them and be careful). Make
3466 note that the rows of data are defined as png_bytepp, which is an
3467 unsigned char far * far *.
3469 .SS Configuring for gui/windowing platforms:
3471 You will need to write new error and warning functions that use the GUI
3472 interface, as described previously, and set them to be the error and
3473 warning functions at the time that png_create_*_struct() is called,
3474 in order to have them available during the structure initialization.
3475 They can be changed later via png_set_error_fn(). On some compilers,
3476 you may also have to change the memory allocators (png_malloc, etc.).
3478 .SS Configuring for compiler xxx:
3480 All includes for libpng are in pngconf.h. If you need to add, change
3481 or delete an include, this is the place to do it.
3482 The includes that are not needed outside libpng are placed in pngpriv.h,
3483 which is only used by the routines inside libpng itself.
3484 The files in libpng proper only include pngpriv.h and png.h, which
3485 in turn includes pngconf.h.
3487 .SS Configuring zlib:
3489 There are special functions to configure the compression. Perhaps the
3490 most useful one changes the compression level, which currently uses
3491 input compression values in the range 0 - 9. The library normally
3492 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3493 have shown that for a large majority of images, compression values in
3494 the range 3-6 compress nearly as well as higher levels, and do so much
3495 faster. For online applications it may be desirable to have maximum speed
3496 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3497 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3498 files larger than just storing the raw bitmap. You can specify the
3499 compression level by calling:
3501 png_set_compression_level(png_ptr, level);
3503 Another useful one is to reduce the memory level used by the library.
3504 The memory level defaults to 8, but it can be lowered if you are
3505 short on memory (running DOS, for example, where you only have 640K).
3506 Note that the memory level does have an effect on compression; among
3507 other things, lower levels will result in sections of incompressible
3508 data being emitted in smaller stored blocks, with a correspondingly
3509 larger relative overhead of up to 15% in the worst case.
3511 png_set_compression_mem_level(png_ptr, level);
3513 The other functions are for configuring zlib. They are not recommended
3514 for normal use and may result in writing an invalid PNG file. See
3515 zlib.h for more information on what these mean.
3517 png_set_compression_strategy(png_ptr,
3519 png_set_compression_window_bits(png_ptr,
3521 png_set_compression_method(png_ptr, method);
3522 png_set_compression_buffer_size(png_ptr, size);
3524 .SS Controlling row filtering
3526 If you want to control whether libpng uses filtering or not, which
3527 filters are used, and how it goes about picking row filters, you
3528 can call one of these functions. The selection and configuration
3529 of row filters can have a significant impact on the size and
3530 encoding speed and a somewhat lesser impact on the decoding speed
3531 of an image. Filtering is enabled by default for RGB and grayscale
3532 images (with and without alpha), but not for paletted images nor
3533 for any images with bit depths less than 8 bits/pixel.
3535 The 'method' parameter sets the main filtering method, which is
3536 currently only '0' in the PNG 1.2 specification. The 'filters'
3537 parameter sets which filter(s), if any, should be used for each
3538 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3539 to turn filtering on and off, respectively.
3541 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3542 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3543 ORed together with '|' to specify one or more filters to use.
3544 These filters are described in more detail in the PNG specification.
3545 If you intend to change the filter type during the course of writing
3546 the image, you should start with flags set for all of the filters
3547 you intend to use so that libpng can initialize its internal
3548 structures appropriately for all of the filter types. (Note that this
3549 means the first row must always be adaptively filtered, because libpng
3550 currently does not allocate the filter buffers until png_write_row()
3551 is called for the first time.)
3553 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3554 PNG_FILTER_UP | PNG_FILTER_AVG |
3555 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3557 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3559 The second parameter can also be
3560 PNG_INTRAPIXEL_DIFFERENCING if you are
3561 writing a PNG to be embedded in a MNG
3562 datastream. This parameter must be the
3563 same as the value of filter_method used
3566 It is also possible to influence how libpng chooses from among the
3567 available filters. This is done in one or both of two ways - by
3568 telling it how important it is to keep the same filter for successive
3569 rows, and by telling it the relative computational costs of the filters.
3571 double weights[3] = {1.5, 1.3, 1.1},
3572 costs[PNG_FILTER_VALUE_LAST] =
3573 {1.0, 1.3, 1.3, 1.5, 1.7};
3575 png_set_filter_heuristics(png_ptr,
3576 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3579 The weights are multiplying factors that indicate to libpng that the
3580 row filter should be the same for successive rows unless another row filter
3581 is that many times better than the previous filter. In the above example,
3582 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3583 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3584 and still be chosen, while the NONE filter could have a sum 1.1 times
3585 higher than other filters and still be chosen. Unspecified weights are
3586 taken to be 1.0, and the specified weights should probably be declining
3587 like those above in order to emphasize recent filters over older filters.
3589 The filter costs specify for each filter type a relative decoding cost
3590 to be considered when selecting row filters. This means that filters
3591 with higher costs are less likely to be chosen over filters with lower
3592 costs, unless their "sum of absolute differences" is that much smaller.
3593 The costs do not necessarily reflect the exact computational speeds of
3594 the various filters, since this would unduly influence the final image
3597 Note that the numbers above were invented purely for this example and
3598 are given only to help explain the function usage. Little testing has
3599 been done to find optimum values for either the costs or the weights.
3601 .SS Removing unwanted object code
3603 There are a bunch of #define's in pngconf.h that control what parts of
3604 libpng are compiled. All the defines end in _SUPPORTED. If you are
3605 never going to use a capability, you can change the #define to #undef
3606 before recompiling libpng and save yourself code and data space, or
3607 you can turn off individual capabilities with defines that begin with
3610 You can also turn all of the transforms and ancillary chunk capabilities
3611 off en masse with compiler directives that define
3612 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3614 along with directives to turn on any of the capabilities that you do
3615 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
3616 transformations but still leave the library fully capable of reading
3617 and writing PNG files with all known public chunks. Use of the
3618 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
3619 that is incapable of reading or writing ancillary chunks. If you are
3620 not using the progressive reading capability, you can turn that off
3621 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
3622 capability, which you'll still have).
3624 All the reading and writing specific code are in separate files, so the
3625 linker should only grab the files it needs. However, if you want to
3626 make sure, or if you are building a stand alone library, all the
3627 reading files start with pngr and all the writing files start with
3628 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3629 are used for both reading and writing, and always need to be included.
3630 The progressive reader is in pngpread.c
3632 If you are creating or distributing a dynamically linked library (a .so
3633 or DLL file), you should not remove or disable any parts of the library,
3634 as this will cause applications linked with different versions of the
3635 library to fail if they call functions not available in your library.
3636 The size of the library itself should not be an issue, because only
3637 those sections that are actually used will be loaded into memory.
3639 .SS Requesting debug printout
3641 The macro definition PNG_DEBUG can be used to request debugging
3642 printout. Set it to an integer value in the range 0 to 3. Higher
3643 numbers result in increasing amounts of debugging information. The
3644 information is printed to the "stderr" file, unless another file
3645 name is specified in the PNG_DEBUG_FILE macro definition.
3647 When PNG_DEBUG > 0, the following functions (macros) become available:
3649 png_debug(level, message)
3650 png_debug1(level, message, p1)
3651 png_debug2(level, message, p1, p2)
3653 in which "level" is compared to PNG_DEBUG to decide whether to print
3654 the message, "message" is the formatted string to be printed,
3655 and p1 and p2 are parameters that are to be embedded in the string
3656 according to printf-style formatting directives. For example,
3658 png_debug1(2, "foo=%d\n", foo);
3663 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3665 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3666 can still use PNG_DEBUG to control your own debugging:
3672 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3673 having level = 0 will be printed. There aren't any such statements in
3674 this version of libpng, but if you insert some they will be printed.
3678 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3679 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3680 Libpng can support some of these extensions. To enable them, use the
3681 png_permit_mng_features() function:
3683 feature_set = png_permit_mng_features(png_ptr, mask)
3684 mask is a png_uint_32 containing the bitwise OR of the
3685 features you want to enable. These include
3686 PNG_FLAG_MNG_EMPTY_PLTE
3687 PNG_FLAG_MNG_FILTER_64
3688 PNG_ALL_MNG_FEATURES
3689 feature_set is a png_uint_32 that is the bitwise AND of
3690 your mask with the set of MNG features that is
3691 supported by the version of libpng that you are using.
3693 It is an error to use this function when reading or writing a standalone
3694 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3695 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3696 and the MHDR and MEND chunks. Libpng does not provide support for these
3697 or any other MNG chunks; your application must provide its own support for
3698 them. You may wish to consider using libmng (available at
3699 http://www.libmng.com) instead.
3701 .SH VII. Changes to Libpng from version 0.88
3703 It should be noted that versions of libpng later than 0.96 are not
3704 distributed by the original libpng author, Guy Schalnat, nor by
3705 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3706 distributed versions 0.89 through 0.96, but rather by another member
3707 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3708 still alive and well, but they have moved on to other things.
3710 The old libpng functions png_read_init(), png_write_init(),
3711 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3712 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3713 functions will be removed from libpng version 2.0.0.
3715 The preferred method of creating and initializing the libpng structures is
3716 via the png_create_read_struct(), png_create_write_struct(), and
3717 png_create_info_struct() because they isolate the size of the structures
3718 from the application, allow version error checking, and also allow the
3719 use of custom error handling routines during the initialization, which
3720 the old functions do not. The functions png_read_destroy() and
3721 png_write_destroy() do not actually free the memory that libpng
3722 allocated for these structs, but just reset the data structures, so they
3723 can be used instead of png_destroy_read_struct() and
3724 png_destroy_write_struct() if you feel there is too much system overhead
3725 allocating and freeing the png_struct for each image read.
3727 Setting the error callbacks via png_set_message_fn() before
3728 png_read_init() as was suggested in libpng-0.88 is no longer supported
3729 because this caused applications that do not use custom error functions
3730 to fail if the png_ptr was not initialized to zero. It is still possible
3731 to set the error callbacks AFTER png_read_init(), or to change them with
3732 png_set_error_fn(), which is essentially the same function, but with a new
3733 name to force compilation errors with applications that try to use the old
3736 Starting with version 1.0.7, you can find out which version of the library
3737 you are using at run-time:
3739 png_uint_32 libpng_vn = png_access_version_number();
3741 The number libpng_vn is constructed from the major version, minor
3742 version with leading zero, and release number with leading zero,
3743 (e.g., libpng_vn for version 1.0.7 is 10007).
3745 You can also check which version of png.h you used when compiling your
3748 png_uint_32 application_vn = PNG_LIBPNG_VER;
3750 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
3752 Support for user memory management was enabled by default. To
3753 accomplish this, the functions png_create_read_struct_2(),
3754 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
3755 png_malloc_default(), and png_free_default() were added.
3757 Support for the iTXt chunk has been enabled by default as of
3760 Support for certain MNG features was enabled.
3762 Support for numbered error messages was added. However, we never got
3763 around to actually numbering the error messages. The function
3764 png_set_strip_error_numbers() was added (Note: the prototype for this
3765 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
3766 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
3768 The png_malloc_warn() function was added at libpng-1.2.3. This issues
3769 a png_warning and returns NULL instead of aborting when it fails to
3770 acquire the requested memory allocation.
3772 Support for setting user limits on image width and height was enabled
3773 by default. The functions png_set_user_limits(), png_get_user_width_max(),
3774 and png_get_user_height_max() were added at libpng-1.2.6.
3776 The png_set_add_alpha() function was added at libpng-1.2.7.
3778 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
3779 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
3780 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
3783 A number of macro definitions in support of runtime selection of
3784 assembler code features (especially Intel MMX code support) were
3785 added at libpng-1.2.0:
3787 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
3788 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
3789 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
3790 PNG_ASM_FLAG_MMX_READ_INTERLACE
3791 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
3792 PNG_ASM_FLAG_MMX_READ_FILTER_UP
3793 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
3794 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
3795 PNG_ASM_FLAGS_INITIALIZED
3801 We added the following functions in support of runtime
3802 selection of assembler code features:
3804 png_get_mmx_flagmask()
3805 png_set_mmx_thresholds()
3807 png_get_mmx_bitdepth_threshold()
3808 png_get_mmx_rowbytes_threshold()
3811 We replaced all of these functions with simple stubs in libpng-1.2.20,
3812 when the Intel assembler code was removed due to a licensing issue.
3814 These macros are deprecated:
3816 PNG_READ_TRANSFORMS_NOT_SUPPORTED
3817 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
3818 PNG_NO_SEQUENTIAL_READ_SUPPORTED
3819 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
3820 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
3821 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
3823 They have been replaced, respectively, by:
3825 PNG_NO_READ_TRANSFORMS
3826 PNG_NO_PROGRESSIVE_READ
3827 PNG_NO_SEQUENTIAL_READ
3828 PNG_NO_WRITE_TRANSFORMS
3829 PNG_NO_READ_ANCILLARY_CHUNKS
3830 PNG_NO_WRITE_ANCILLARY_CHUNKS
3832 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
3833 deprecated since libpng-1.0.16 and libpng-1.2.6.
3836 png_check_sig(sig, num)
3838 !png_sig_cmp(sig, 0, num)
3839 It has been deprecated since libpng-0.90.
3842 png_set_gray_1_2_4_to_8()
3843 which also expands tRNS to alpha was replaced with
3844 png_set_expand_gray_1_2_4_to_8()
3845 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
3847 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
3849 Private libpng prototypes and macro definitions were moved from
3850 png.h and pngconf.h into a new pngpriv.h header file.
3852 Functions png_set_benign_errors(), png_benign_error(), and
3853 png_chunk_benign_error() were added.
3855 Support for setting the maximum amount of memory that the application
3856 will allocate for reading chunks was added, as a security measure.
3857 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
3858 were added to the library.
3860 We implemented support for I/O states by adding png_ptr member io_state
3861 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
3863 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
3866 Checking for and reporting of errors in the IHDR chunk is more thorough.
3868 Support for global arrays was removed, to improve thread safety.
3870 Some obsolete/deprecated macros and functions have been removed.
3872 Typecasted NULL definitions such as
3873 #define png_voidp_NULL (png_voidp)NULL
3874 were eliminated. If you used these in your application, just use
3877 The png_struct and info_struct members "trans" and "trans_values" were
3878 changed to "trans_alpha" and "trans_color", respectively.
3880 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
3883 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
3885 The PNG_LEGACY_SUPPORTED macro was eliminated.
3887 Many WIN32_WCE #ifdefs were removed.
3889 The functions png_read_init(info_ptr), png_write_init(info_ptr),
3890 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
3891 have been removed. They have been deprecated since libpng-0.95.
3893 The png_permit_empty_plte() was removed. It has been deprecated
3894 since libpng-1.0.9. Use png_permit_mng_features() instead.
3896 We removed the obsolete stub functions png_get_mmx_flagmask(),
3897 png_set_mmx_thresholds(), png_get_asm_flags(),
3898 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
3899 png_set_asm_flags(), and png_mmx_supported()
3901 We removed the obsolete png_check_sig(), png_memcpy_check(), and
3902 png_memset_check() functions. Instead use !png_sig_cmp(), png_memcpy(),
3903 and png_memset(), respectively.
3905 The function png_set_gray_1_2_4_to_8() was removed. It has been
3906 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
3907 png_set_expand_gray_1_2_4_to_8() because the former function also
3908 expanded palette images.
3910 We changed the prototype for png_malloc() from
3911 png_malloc(png_structp png_ptr, png_uint_32 size)
3913 png_malloc(png_structp png_ptr, png_alloc_size_t size)
3915 This also applies to the prototype for the user replacement malloc_fn().
3917 The png_calloc() function was added and is used in place of
3918 of "png_malloc(); png_memset();" except in the case in png_read_png()
3919 where the array consists of pointers; in this case a "for" loop is used
3920 after the png_malloc() to set the pointers to NULL, to give robust.
3921 behavior in case the application runs out of memory part-way through
3924 We changed the prototypes of png_get_compression_buffer_size() and
3925 png_set_compression_buffer_size() to work with png_size_t instead of
3928 Support for numbered error messages was removed by default, since we
3929 never got around to actually numbering the error messages. The function
3930 png_set_strip_error_numbers() was removed from the library by default.
3932 The png_zalloc() and png_zfree() functions are no longer exported.
3933 The png_zalloc() function no longer zeroes out the memory that it
3936 Support for dithering was disabled by default in libpng-1.4.0, because
3937 been well tested and doesn't actually "dither". The code was not
3938 removed, however, and could be enabled by building libpng with
3939 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
3940 was reenabled, but the function was renamed png_set_quantize() to
3941 reflect more accurately what it actually does. At the same time,
3942 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
3943 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS.
3945 We removed the trailing '.' from the warning and error messages.
3947 .SH X. Detecting libpng
3949 The png_get_io_ptr() function has been present since libpng-0.88, has never
3950 changed, and is unaffected by conditional compilation macros. It is the
3951 best choice for use in configure scripts for detecting the presence of any
3952 libpng version since 0.88. In an autoconf "configure.in" you could use
3954 AC_CHECK_LIB(png, png_get_io_ptr, ...
3956 .SH XI. Source code repository
3958 Since about February 2009, version 1.2.34, libpng has been under "git" source
3959 control. The git repository was built from old libpng-x.y.z.tar.gz files
3960 going back to version 0.70. You can access the git repository (read only)
3963 git://libpng.git.sourceforge.net/gitroot/libpng
3965 or you can browse it via "gitweb" at
3967 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
3969 Patches can be sent to glennrp at users.sourceforge.net or to
3970 png-mng-implement at lists.sourceforge.net or you can upload them to
3971 the libpng bug tracker at
3973 http://libpng.sourceforge.net
3975 .SH XII. Coding style
3977 Our coding style is similar to the "Allman" style, with curly
3978 braces on separate lines:
3985 else if (another condition)
3990 The braces can be omitted from simple one-line actions:
3995 We use 3-space indentation, except for continued statements which
3996 are usually indented the same as the first line of the statement
3997 plus four more spaces.
3999 For macro definitions we use 2-space indentation, always leaving the "#"
4000 in the first column.
4002 #ifndef PNG_NO_FEATURE
4003 # ifndef PNG_FEATURE_SUPPORTED
4004 # define PNG_FEATURE_SUPPORTED
4008 Comments appear with the leading "/*" at the same indentation as
4009 the statement that follows the comment:
4011 /* Single-line comment */
4014 /* This is a multiple-line
4019 Very short comments can be placed after the end of the statement
4020 to which they pertain:
4022 statement; /* comment */
4024 We don't use C++ style ("//") comments. We have, however,
4025 used them in the past in some now-abandoned MMX assembler
4028 Functions and their curly braces are not indented, and
4029 exported functions are marked with PNGAPI:
4031 /* This is a public function that is visible to
4032 * application programers. It does thus-and-so.
4035 png_exported_function(png_ptr, png_info, foo)
4040 The prototypes for all exported functions appear in png.h,
4041 above the comment that says
4043 /* Maintainer: Put new public prototypes here ... */
4045 We mark all non-exported functions with "/* PRIVATE */"":
4048 png_non_exported_function(png_ptr, png_info, foo)
4053 The prototypes for non-exported functions (except for those in
4056 above the comment that says
4058 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
4060 The names of all exported functions and variables begin
4061 with "png_", and all publicly visible C preprocessor
4062 macros begin with "PNG_".
4064 We put a space after each comma and after each semicolon
4065 in "for" statments, and we put spaces before and after each
4066 C binary operator and after "for" or "while", and before
4067 "?". We don't put a space between a typecast and the expression
4068 being cast, nor do we put one between a function name and the
4069 left parenthesis that follows it:
4071 for (i = 2; i > 0; --i)
4072 y[i] = a(x) + (int)b;
4074 We prefer #ifdef and #ifndef to #if defined() and if !defined()
4075 when there is only one macro being tested.
4077 We do not use the TAB character for indentation in the C sources.
4079 Lines do not exceed 80 characters.
4081 Other rules can be inferred by inspecting the libpng source.
4083 .SH XIII. Y2K Compliance in libpng
4087 Since the PNG Development group is an ad-hoc body, we can't make
4088 an official declaration.
4090 This is your unofficial assurance that libpng from version 0.71 and
4091 upward through 1.4.3 are Y2K compliant. It is my belief that earlier
4092 versions were also Y2K compliant.
4094 Libpng only has three year fields. One is a 2-byte unsigned integer that
4095 will hold years up to 65535. The other two hold the date in text
4096 format, and will hold years up to 9999.
4099 "png_uint_16 year" in png_time_struct.
4102 "png_charp time_buffer" in png_struct and
4103 "near_time_buffer", which is a local character string in png.c.
4105 There are seven time-related functions:
4107 png_convert_to_rfc_1123() in png.c
4108 (formerly png_convert_to_rfc_1152() in error)
4109 png_convert_from_struct_tm() in pngwrite.c, called
4111 png_convert_from_time_t() in pngwrite.c
4112 png_get_tIME() in pngget.c
4113 png_handle_tIME() in pngrutil.c, called in pngread.c
4114 png_set_tIME() in pngset.c
4115 png_write_tIME() in pngwutil.c, called in pngwrite.c
4117 All appear to handle dates properly in a Y2K environment. The
4118 png_convert_from_time_t() function calls gmtime() to convert from system
4119 clock time, which returns (year - 1900), which we properly convert to
4120 the full 4-digit year. There is a possibility that applications using
4121 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
4122 function, or that they are incorrectly passing only a 2-digit year
4123 instead of "year - 1900" into the png_convert_from_struct_tm() function,
4124 but this is not under our control. The libpng documentation has always
4125 stated that it works with 4-digit years, and the APIs have been
4128 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
4129 integer to hold the year, and can hold years as large as 65535.
4131 zlib, upon which libpng depends, is also Y2K compliant. It contains
4132 no date-related code.
4135 Glenn Randers-Pehrson
4137 PNG Development Group
4141 Note about libpng version numbers:
4143 Due to various miscommunications, unforeseen code incompatibilities
4144 and occasional factors outside the authors' control, version numbering
4145 on the library has not always been consistent and straightforward.
4146 The following table summarizes matters since version 0.89c, which was
4147 the first widely used release:
4149 source png.h png.h shared-lib
4150 version string int version
4151 ------- ------ ----- ----------
4152 0.89c ("beta 3") 0.89 89 1.0.89
4153 0.90 ("beta 4") 0.90 90 0.90
4154 0.95 ("beta 5") 0.95 95 0.95
4155 0.96 ("beta 6") 0.96 96 0.96
4156 0.97b ("beta 7") 1.00.97 97 1.0.1
4157 0.97c 0.97 97 2.0.97
4160 0.99a-m 0.99 99 2.0.99
4162 1.0.0 1.0.0 100 2.1.0
4163 1.0.0 (from here on, the 100 2.1.0
4164 1.0.1 png.h string is 10001 2.1.0
4165 1.0.1a-e identical to the 10002 from here on, the
4166 1.0.2 source version) 10002 shared library is 2.V
4167 1.0.2a-b 10003 where V is the source
4168 1.0.1 10001 code version except as
4169 1.0.1a-e 10002 2.1.0.1a-e noted.
4171 1.0.2a-b 10003 2.1.0.2a-b
4173 1.0.3a-d 10004 2.1.0.3a-d
4175 1.0.4a-f 10005 2.1.0.4a-f
4176 1.0.5 (+ 2 patches) 10005 2.1.0.5
4177 1.0.5a-d 10006 2.1.0.5a-d
4178 1.0.5e-r 10100 2.1.0.5e-r
4179 1.0.5s-v 10006 2.1.0.5s-v
4180 1.0.6 (+ 3 patches) 10006 2.1.0.6
4181 1.0.6d-g 10007 2.1.0.6d-g
4184 1.0.6j 10007 2.1.0.6j
4185 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
4186 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
4187 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
4188 1.0.7 1 10007 2.1.0.7
4189 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
4190 1.0.8rc1 1 10008 2.1.0.8rc1
4191 1.0.8 1 10008 2.1.0.8
4192 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
4193 1.0.9rc1 1 10009 2.1.0.9rc1
4194 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
4195 1.0.9rc2 1 10009 2.1.0.9rc2
4196 1.0.9 1 10009 2.1.0.9
4197 1.0.10beta1 1 10010 2.1.0.10beta1
4198 1.0.10rc1 1 10010 2.1.0.10rc1
4199 1.0.10 1 10010 2.1.0.10
4200 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
4201 1.0.11rc1 1 10011 2.1.0.11rc1
4202 1.0.11 1 10011 2.1.0.11
4203 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
4204 1.0.12rc1 2 10012 2.1.0.12rc1
4205 1.0.12 2 10012 2.1.0.12
4206 1.1.0a-f - 10100 2.1.1.0a-f abandoned
4207 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
4208 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
4209 1.2.0rc1 3 10200 3.1.2.0rc1
4210 1.2.0 3 10200 3.1.2.0
4211 1.2.1beta-4 3 10201 3.1.2.1beta1-4
4212 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
4213 1.2.1 3 10201 3.1.2.1
4214 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
4215 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
4216 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
4217 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
4218 1.0.13 10 10013 10.so.0.1.0.13
4219 1.2.2 12 10202 12.so.0.1.2.2
4220 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
4221 1.2.3 12 10203 12.so.0.1.2.3
4222 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
4223 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
4224 1.0.14 10 10014 10.so.0.1.0.14
4225 1.2.4 13 10204 12.so.0.1.2.4
4226 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
4227 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
4228 1.0.15 10 10015 10.so.0.1.0.15
4229 1.2.5 13 10205 12.so.0.1.2.5
4230 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
4231 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
4232 1.0.16 10 10016 10.so.0.1.0.16
4233 1.2.6 13 10206 12.so.0.1.2.6
4234 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
4235 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
4236 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
4237 1.0.17 10 10017 12.so.0.1.0.17
4238 1.2.7 13 10207 12.so.0.1.2.7
4239 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
4240 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
4241 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
4242 1.0.18 10 10018 12.so.0.1.0.18
4243 1.2.8 13 10208 12.so.0.1.2.8
4244 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
4245 1.2.9beta4-11 13 10209 12.so.0.9[.0]
4246 1.2.9rc1 13 10209 12.so.0.9[.0]
4247 1.2.9 13 10209 12.so.0.9[.0]
4248 1.2.10beta1-7 13 10210 12.so.0.10[.0]
4249 1.2.10rc1-2 13 10210 12.so.0.10[.0]
4250 1.2.10 13 10210 12.so.0.10[.0]
4251 1.4.0beta1-6 14 10400 14.so.0.0[.0]
4252 1.2.11beta1-4 13 10210 12.so.0.11[.0]
4253 1.4.0beta7-8 14 10400 14.so.0.0[.0]
4254 1.2.11 13 10211 12.so.0.11[.0]
4255 1.2.12 13 10212 12.so.0.12[.0]
4256 1.4.0beta9-14 14 10400 14.so.0.0[.0]
4257 1.2.13 13 10213 12.so.0.13[.0]
4258 1.4.0beta15-36 14 10400 14.so.0.0[.0]
4259 1.4.0beta37-87 14 10400 14.so.14.0[.0]
4260 1.4.0rc01 14 10400 14.so.14.0[.0]
4261 1.4.0beta88-109 14 10400 14.so.14.0[.0]
4262 1.4.0rc02-08 14 10400 14.so.14.0[.0]
4263 1.4.0 14 10400 14.so.14.0[.0]
4264 1.4.1beta01-03 14 10401 14.so.14.1[.0]
4265 1.4.1rc01 14 10401 14.so.14.1[.0]
4266 1.4.1beta04-12 14 10401 14.so.14.1[.0]
4267 1.4.1rc02-04 14 10401 14.so.14.1[.0]
4268 1.4.1 14 10401 14.so.14.1[.0]
4269 1.4.2beta01 14 10402 14.so.14.2[.0]
4270 1.4.2rc02-06 14 10402 14.so.14.2[.0]
4271 1.4.2 14 10402 14.so.14.2[.0]
4272 1.4.3beta01-05 14 10403 14.so.14.3[.0]
4273 1.4.3rc01-03 14 10403 14.so.14.3[.0]
4274 1.4.3 14 10403 14.so.14.3[.0]
4276 Henceforth the source version will match the shared-library minor
4277 and patch numbers; the shared-library major version number will be
4278 used for changes in backward compatibility, as it is intended. The
4279 PNG_PNGLIB_VER macro, which is not used within libpng but is available
4280 for applications, is an unsigned integer of the form xyyzz corresponding
4281 to the source version x.y.z (leading zeros in y and z). Beta versions
4282 were given the previous public release number plus a letter, until
4283 version 1.0.6j; from then on they were given the upcoming public
4284 release number plus "betaNN" or "rcN".
4291 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
4292 http://www.libpng.org/pub/png
4297 (generally) at the same location as
4301 ftp://ftp.info-zip.org/pub/infozip/zlib
4304 .IR PNG specification: RFC 2083
4306 (generally) at the same location as
4310 ftp://ds.internic.net/rfc/rfc2083.txt
4312 or (as a W3C Recommendation) at
4314 http://www.w3.org/TR/REC-png.html
4317 In the case of any inconsistency between the PNG specification
4318 and this library, the specification takes precedence.
4321 This man page: Glenn Randers-Pehrson
4322 <glennrp at users.sourceforge.net>
4324 The contributing authors would like to thank all those who helped
4325 with testing, bug fixes, and patience. This wouldn't have been
4326 possible without all of you.
4328 Thanks to Frank J. T. Wojcik for helping with the documentation.
4330 Libpng version 1.4.3 - June 26, 2010:
4331 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
4332 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
4334 Supported by the PNG development group
4336 png-mng-implement at lists.sf.net
4337 (subscription required; visit
4338 png-mng-implement at lists.sourceforge.net (subscription required; visit
4339 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
4342 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
4344 (This copy of the libpng notices is provided for your convenience. In case of
4345 any discrepancy between this copy and the notices in the file png.h that is
4346 included in the libpng distribution, the latter shall prevail.)
4348 If you modify libpng you may insert additional notices immediately following
4351 This code is released under the libpng license.
4353 libpng versions 1.2.6, August 15, 2004, through 1.4.3, June 26, 2010, are
4354 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
4355 distributed according to the same disclaimer and license as libpng-1.2.5
4356 with the following individual added to the list of Contributing Authors
4360 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
4361 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
4362 distributed according to the same disclaimer and license as libpng-1.0.6
4363 with the following individuals added to the list of Contributing Authors
4365 Simon-Pierre Cadieux
4369 and with the following additions to the disclaimer:
4371 There is no warranty against interference with your
4372 enjoyment of the library or against infringement.
4373 There is no warranty that our efforts or the library
4374 will fulfill any of your particular purposes or needs.
4375 This library is provided with all faults, and the entire
4376 risk of satisfactory quality, performance, accuracy, and
4377 effort is with the user.
4379 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
4380 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
4381 Distributed according to the same disclaimer and license as libpng-0.96,
4382 with the following individuals added to the list of Contributing Authors:
4385 Glenn Randers-Pehrson
4388 libpng versions 0.89, June 1996, through 0.96, May 1997, are
4389 Copyright (c) 1996, 1997 Andreas Dilger
4390 Distributed according to the same disclaimer and license as libpng-0.88,
4391 with the following individuals added to the list of Contributing Authors:
4400 libpng versions 0.5, May 1995, through 0.88, January 1996, are
4401 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
4403 For the purposes of this copyright and license, "Contributing Authors"
4404 is defined as the following set of individuals:
4412 The PNG Reference Library is supplied "AS IS". The Contributing Authors
4413 and Group 42, Inc. disclaim all warranties, expressed or implied,
4414 including, without limitation, the warranties of merchantability and of
4415 fitness for any purpose. The Contributing Authors and Group 42, Inc.
4416 assume no liability for direct, indirect, incidental, special, exemplary,
4417 or consequential damages, which may result from the use of the PNG
4418 Reference Library, even if advised of the possibility of such damage.
4420 Permission is hereby granted to use, copy, modify, and distribute this
4421 source code, or portions hereof, for any purpose, without fee, subject
4422 to the following restrictions:
4424 1. The origin of this source code must not be misrepresented.
4426 2. Altered versions must be plainly marked as such and
4427 must not be misrepresented as being the original source.
4429 3. This Copyright notice may not be removed or altered from
4430 any source or altered source distribution.
4432 The Contributing Authors and Group 42, Inc. specifically permit, without
4433 fee, and encourage the use of this source code as a component to
4434 supporting the PNG file format in commercial products. If you use this
4435 source code in a product, acknowledgment is not required but would be
4439 A "png_get_copyright" function is available, for convenient use in "about"
4442 printf("%s",png_get_copyright(NULL));
4444 Also, the PNG logo (in PNG format, of course) is supplied in the
4445 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4447 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4448 certification mark of the Open Source Initiative.
4450 Glenn Randers-Pehrson
4451 glennrp at users.sourceforge.net
projects / l4.git / blob