1 .TH LIBPNG 3 "February 25, 2010"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.4.1
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_dither (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_dither\fP\fB);\fP
461 \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
465 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
469 \fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
473 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
477 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
481 \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
485 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
489 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
493 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
497 \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
501 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
505 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
509 \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
513 \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
517 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
521 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
525 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
529 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
533 \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
537 \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
541 \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
545 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
549 \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
553 \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
557 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
561 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
565 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
569 \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
573 \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
577 \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
581 \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
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 1.4.1 - February 25, 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 1.4.1 - February 25, 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_SETJMP_NOT_SUPPORTED, in which case
1030 errors will result in a call to PNG_ABORT() which defaults to abort().
1032 Now you need to set up the input code. The default for libpng is to
1033 use the C function fread(). If you use this, you will need to pass a
1034 valid FILE * in the function png_init_io(). Be sure that the file is
1035 opened in binary mode. If you wish to handle reading data in another
1036 way, you need not call the png_init_io() function, but you must then
1037 implement the libpng I/O methods discussed in the Customizing Libpng
1040 png_init_io(png_ptr, fp);
1042 If you had previously opened the file and read any of the signature from
1043 the beginning in order to see if this was a PNG file, you need to let
1044 libpng know that there are some bytes missing from the start of the file.
1046 png_set_sig_bytes(png_ptr, number);
1048 You can change the zlib compression buffer size to be used while
1049 reading compressed data with
1051 png_set_compression_buffer_size(png_ptr, buffer_size);
1053 where the default size is 8192 bytes. Note that the buffer size
1054 is changed immediately and the buffer is reallocated immediately,
1055 instead of setting a flag to be acted upon later.
1057 .SS Setting up callback code
1059 You can set up a callback function to handle any unknown chunks in the
1060 input stream. You must supply the function
1062 read_chunk_callback(png_ptr ptr,
1063 png_unknown_chunkp chunk);
1065 /* The unknown chunk structure contains your
1066 chunk data, along with similar data for any other
1073 /* Note that libpng has already taken care of
1076 /* put your code here. Search for your chunk in the
1077 unknown chunk structure, process it, and return one
1078 of the following: */
1080 return (-n); /* chunk had an error */
1081 return (0); /* did not recognize */
1082 return (n); /* success */
1085 (You can give your function another name that you like instead of
1086 "read_chunk_callback")
1088 To inform libpng about your function, use
1090 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1091 read_chunk_callback);
1093 This names not only the callback function, but also a user pointer that
1094 you can retrieve with
1096 png_get_user_chunk_ptr(png_ptr);
1098 If you call the png_set_read_user_chunk_fn() function, then all unknown
1099 chunks will be saved when read, in case your callback function will need
1100 one or more of them. This behavior can be changed with the
1101 png_set_keep_unknown_chunks() function, described below.
1103 At this point, you can set up a callback function that will be
1104 called after each row has been read, which you can use to control
1105 a progress meter or the like. It's demonstrated in pngtest.c.
1106 You must supply a function
1108 void read_row_callback(png_ptr ptr, png_uint_32 row,
1111 /* put your code here */
1114 (You can give it another name that you like instead of "read_row_callback")
1116 To inform libpng about your function, use
1118 png_set_read_status_fn(png_ptr, read_row_callback);
1120 .SS Unknown-chunk handling
1122 Now you get to set the way the library processes unknown chunks in the
1123 input PNG stream. Both known and unknown chunks will be read. Normal
1124 behavior is that known chunks will be parsed into information in
1125 various info_ptr members while unknown chunks will be discarded. This
1126 behavior can be wasteful if your application will never use some known
1127 chunk types. To change this, you can call:
1129 png_set_keep_unknown_chunks(png_ptr, keep,
1130 chunk_list, num_chunks);
1131 keep - 0: default unknown chunk handling
1132 1: ignore; do not keep
1133 2: keep only if safe-to-copy
1134 3: keep even if unsafe-to-copy
1135 You can use these definitions:
1136 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1137 PNG_HANDLE_CHUNK_NEVER 1
1138 PNG_HANDLE_CHUNK_IF_SAFE 2
1139 PNG_HANDLE_CHUNK_ALWAYS 3
1140 chunk_list - list of chunks affected (a byte string,
1141 five bytes per chunk, NULL or '\0' if
1143 num_chunks - number of chunks affected; if 0, all
1144 unknown chunks are affected. If nonzero,
1145 only the chunks in the list are affected
1147 Unknown chunks declared in this way will be saved as raw data onto a
1148 list of png_unknown_chunk structures. If a chunk that is normally
1149 known to libpng is named in the list, it will be handled as unknown,
1150 according to the "keep" directive. If a chunk is named in successive
1151 instances of png_set_keep_unknown_chunks(), the final instance will
1152 take precedence. The IHDR and IEND chunks should not be named in
1153 chunk_list; if they are, libpng will process them normally anyway.
1155 Here is an example of the usage of png_set_keep_unknown_chunks(),
1156 where the private "vpAg" chunk will later be processed by a user chunk
1159 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1161 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1162 png_byte unused_chunks[]=
1164 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1165 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1166 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1167 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1168 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1169 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1175 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1176 /* ignore all unknown chunks: */
1177 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1178 /* except for vpAg: */
1179 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1180 /* also ignore unused known chunks: */
1181 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1182 (int)sizeof(unused_chunks)/5);
1187 The PNG specification allows the width and height of an image to be as
1188 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1189 Since very few applications really need to process such large images,
1190 we have imposed an arbitrary 1-million limit on rows and columns.
1191 Larger images will be rejected immediately with a png_error() call. If
1192 you wish to override this limit, you can use
1194 png_set_user_limits(png_ptr, width_max, height_max);
1196 to set your own limits, or use width_max = height_max = 0x7fffffffL
1197 to allow all valid dimensions (libpng may reject some very large images
1198 anyway because of potential buffer overflow conditions).
1200 You should put this statement after you create the PNG structure and
1201 before calling png_read_info(), png_read_png(), or png_process_data().
1202 If you need to retrieve the limits that are being applied, use
1204 width_max = png_get_user_width_max(png_ptr);
1205 height_max = png_get_user_height_max(png_ptr);
1207 The PNG specification sets no limit on the number of ancillary chunks
1208 allowed in a PNG datastream. You can impose a limit on the total number
1209 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1211 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1213 where 0x7fffffffL means unlimited. You can retrieve this limit with
1215 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1217 This limit also applies to the number of buffers that can be allocated
1218 by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1220 You can also set a limit on the amount of memory that a compressed chunk
1221 other than IDAT can occupy, with
1223 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1225 and you can retrieve the limit with
1227 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1229 Any chunks that would cause either of these limits to be exceeded will
1232 .SS The high-level read interface
1234 At this point there are two ways to proceed; through the high-level
1235 read interface, or through a sequence of low-level read operations.
1236 You can use the high-level interface if (a) you are willing to read
1237 the entire image into memory, and (b) the input transformations
1238 you want to do are limited to the following set:
1240 PNG_TRANSFORM_IDENTITY No transformation
1241 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1243 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1244 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1246 PNG_TRANSFORM_PACKSWAP Change order of packed
1248 PNG_TRANSFORM_EXPAND Perform set_expand()
1249 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1250 PNG_TRANSFORM_SHIFT Normalize pixels to the
1252 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1254 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1256 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1258 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1259 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1260 to RGB (or GA to RGBA)
1262 (This excludes setting a background color, doing gamma transformation,
1263 dithering, and setting filler.) If this is the case, simply do this:
1265 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1267 where png_transforms is an integer containing the bitwise OR of some
1268 set of transformation flags. This call is equivalent to png_read_info(),
1269 followed the set of transformations indicated by the transform mask,
1270 then png_read_image(), and finally png_read_end().
1272 (The final parameter of this call is not yet used. Someday it might point
1273 to transformation parameters required by some future input transform.)
1275 You must use png_transforms and not call any png_set_transform() functions
1276 when you use png_read_png().
1278 After you have called png_read_png(), you can retrieve the image data
1281 row_pointers = png_get_rows(png_ptr, info_ptr);
1283 where row_pointers is an array of pointers to the pixel data for each row:
1285 png_bytep row_pointers[height];
1287 If you know your image size and pixel size ahead of time, you can allocate
1288 row_pointers prior to calling png_read_png() with
1290 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1292 "Image is too tall to process in memory");
1293 if (width > PNG_UINT_32_MAX/pixel_size)
1295 "Image is too wide to process in memory");
1296 row_pointers = png_malloc(png_ptr,
1297 height*png_sizeof(png_bytep));
1298 for (int i=0; i<height, i++)
1299 row_pointers[i]=NULL; /* security precaution */
1300 for (int i=0; i<height, i++)
1301 row_pointers[i]=png_malloc(png_ptr,
1303 png_set_rows(png_ptr, info_ptr, &row_pointers);
1305 Alternatively you could allocate your image in one big block and define
1306 row_pointers[i] to point into the proper places in your block.
1308 If you use png_set_rows(), the application is responsible for freeing
1309 row_pointers (and row_pointers[i], if they were separately allocated).
1311 If you don't allocate row_pointers ahead of time, png_read_png() will
1312 do it, and it'll be free'ed when you call png_destroy_*().
1314 .SS The low-level read interface
1316 If you are going the low-level route, you are now ready to read all
1317 the file information up to the actual image data. You do this with a
1318 call to png_read_info().
1320 png_read_info(png_ptr, info_ptr);
1322 This will process all chunks up to but not including the image data.
1324 .SS Querying the info structure
1326 Functions are used to get the information from the info_ptr once it
1327 has been read. Note that these fields may not be completely filled
1328 in until png_read_end() has read the chunk data following the image.
1330 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1331 &bit_depth, &color_type, &interlace_type,
1332 &compression_type, &filter_method);
1334 width - holds the width of the image
1335 in pixels (up to 2^31).
1336 height - holds the height of the image
1337 in pixels (up to 2^31).
1338 bit_depth - holds the bit depth of one of the
1339 image channels. (valid values are
1340 1, 2, 4, 8, 16 and depend also on
1341 the color_type. See also
1342 significant bits (sBIT) below).
1343 color_type - describes which color/alpha channels
1346 (bit depths 1, 2, 4, 8, 16)
1347 PNG_COLOR_TYPE_GRAY_ALPHA
1349 PNG_COLOR_TYPE_PALETTE
1350 (bit depths 1, 2, 4, 8)
1353 PNG_COLOR_TYPE_RGB_ALPHA
1356 PNG_COLOR_MASK_PALETTE
1357 PNG_COLOR_MASK_COLOR
1358 PNG_COLOR_MASK_ALPHA
1360 filter_method - (must be PNG_FILTER_TYPE_BASE
1361 for PNG 1.0, and can also be
1362 PNG_INTRAPIXEL_DIFFERENCING if
1363 the PNG datastream is embedded in
1364 a MNG-1.0 datastream)
1365 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1367 interlace_type - (PNG_INTERLACE_NONE or
1368 PNG_INTERLACE_ADAM7)
1370 Any or all of interlace_type, compression_type, or
1371 filter_method can be NULL if you are
1372 not interested in their values.
1374 Note that png_get_IHDR() returns 32-bit data into
1375 the application's width and height variables.
1376 This is an unsafe situation if these are 16-bit
1377 variables. In such situations, the
1378 png_get_image_width() and png_get_image_height()
1379 functions described below are safer.
1381 width = png_get_image_width(png_ptr,
1383 height = png_get_image_height(png_ptr,
1385 bit_depth = png_get_bit_depth(png_ptr,
1387 color_type = png_get_color_type(png_ptr,
1389 filter_method = png_get_filter_type(png_ptr,
1391 compression_type = png_get_compression_type(png_ptr,
1393 interlace_type = png_get_interlace_type(png_ptr,
1396 channels = png_get_channels(png_ptr, info_ptr);
1397 channels - number of channels of info for the
1398 color type (valid values are 1 (GRAY,
1399 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1400 4 (RGB_ALPHA or RGB + filler byte))
1401 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1402 rowbytes - number of bytes needed to hold a row
1404 signature = png_get_signature(png_ptr, info_ptr);
1405 signature - holds the signature read from the
1406 file (if any). The data is kept in
1407 the same offset it would be if the
1408 whole signature were read (i.e. if an
1409 application had already read in 4
1410 bytes of signature before starting
1411 libpng, the remaining 4 bytes would
1412 be in signature[4] through signature[7]
1413 (see png_set_sig_bytes())).
1415 These are also important, but their validity depends on whether the chunk
1416 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1417 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1418 data has been read, or zero if it is missing. The parameters to the
1419 png_get_<chunk> are set directly if they are simple data types, or a
1420 pointer into the info_ptr is returned for any complex types.
1422 png_get_PLTE(png_ptr, info_ptr, &palette,
1424 palette - the palette for the file
1425 (array of png_color)
1426 num_palette - number of entries in the palette
1428 png_get_gAMA(png_ptr, info_ptr, &gamma);
1429 gamma - the gamma the file is written
1432 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1433 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1434 The presence of the sRGB chunk
1435 means that the pixel data is in the
1436 sRGB color space. This chunk also
1437 implies specific values of gAMA and
1440 png_get_iCCP(png_ptr, info_ptr, &name,
1441 &compression_type, &profile, &proflen);
1442 name - The profile name.
1443 compression - The compression type; always
1444 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1445 You may give NULL to this argument to
1447 profile - International Color Consortium color
1448 profile data. May contain NULs.
1449 proflen - length of profile data in bytes.
1451 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1452 sig_bit - the number of significant bits for
1453 (PNG_INFO_sBIT) each of the gray,
1454 red, green, and blue channels,
1455 whichever are appropriate for the
1456 given color type (png_color_16)
1458 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1459 &num_trans, &trans_color);
1460 trans_alpha - array of alpha (transparency)
1461 entries for palette (PNG_INFO_tRNS)
1462 trans_color - graylevel or color sample values of
1463 the single transparent color for
1464 non-paletted images (PNG_INFO_tRNS)
1465 num_trans - number of transparent entries
1468 png_get_hIST(png_ptr, info_ptr, &hist);
1470 hist - histogram of palette (array of
1473 png_get_tIME(png_ptr, info_ptr, &mod_time);
1474 mod_time - time image was last modified
1477 png_get_bKGD(png_ptr, info_ptr, &background);
1478 background - background color (PNG_VALID_bKGD)
1479 valid 16-bit red, green and blue
1480 values, regardless of color_type
1482 num_comments = png_get_text(png_ptr, info_ptr,
1483 &text_ptr, &num_text);
1484 num_comments - number of comments
1485 text_ptr - array of png_text holding image
1487 text_ptr[i].compression - type of compression used
1488 on "text" PNG_TEXT_COMPRESSION_NONE
1489 PNG_TEXT_COMPRESSION_zTXt
1490 PNG_ITXT_COMPRESSION_NONE
1491 PNG_ITXT_COMPRESSION_zTXt
1492 text_ptr[i].key - keyword for comment. Must contain
1494 text_ptr[i].text - text comments for current
1495 keyword. Can be empty.
1496 text_ptr[i].text_length - length of text string,
1497 after decompression, 0 for iTXt
1498 text_ptr[i].itxt_length - length of itxt string,
1499 after decompression, 0 for tEXt/zTXt
1500 text_ptr[i].lang - language of comment (empty
1501 string for unknown).
1502 text_ptr[i].lang_key - keyword in UTF-8
1503 (empty string for unknown).
1504 Note that the itxt_length, lang, and lang_key
1505 members of the text_ptr structure only exist
1506 when the library is built with iTXt chunk support.
1508 num_text - number of comments (same as
1509 num_comments; you can put NULL here
1510 to avoid the duplication)
1511 Note while png_set_text() will accept text, language,
1512 and translated keywords that can be NULL pointers, the
1513 structure returned by png_get_text will always contain
1514 regular zero-terminated C strings. They might be
1515 empty strings but they will never be NULL pointers.
1517 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1519 palette_ptr - array of palette structures holding
1520 contents of one or more sPLT chunks
1522 num_spalettes - number of sPLT chunks read.
1524 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1526 offset_x - positive offset from the left edge
1528 offset_y - positive offset from the top edge
1530 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1532 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1534 res_x - pixels/unit physical resolution in
1536 res_y - pixels/unit physical resolution in
1538 unit_type - PNG_RESOLUTION_UNKNOWN,
1539 PNG_RESOLUTION_METER
1541 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1543 unit - physical scale units (an integer)
1544 width - width of a pixel in physical scale units
1545 height - height of a pixel in physical scale units
1546 (width and height are doubles)
1548 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1550 unit - physical scale units (an integer)
1551 width - width of a pixel in physical scale units
1552 height - height of a pixel in physical scale units
1553 (width and height are strings like "2.54")
1555 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1556 info_ptr, &unknowns)
1557 unknowns - array of png_unknown_chunk
1558 structures holding unknown chunks
1559 unknowns[i].name - name of unknown chunk
1560 unknowns[i].data - data of unknown chunk
1561 unknowns[i].size - size of unknown chunk's data
1562 unknowns[i].location - position of chunk in file
1564 The value of "i" corresponds to the order in which the
1565 chunks were read from the PNG file or inserted with the
1566 png_set_unknown_chunks() function.
1568 The data from the pHYs chunk can be retrieved in several convenient
1571 res_x = png_get_x_pixels_per_meter(png_ptr,
1573 res_y = png_get_y_pixels_per_meter(png_ptr,
1575 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1577 res_x = png_get_x_pixels_per_inch(png_ptr,
1579 res_y = png_get_y_pixels_per_inch(png_ptr,
1581 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1583 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1586 (Each of these returns 0 [signifying "unknown"] if
1587 the data is not present or if res_x is 0;
1588 res_x_and_y is 0 if res_x != res_y)
1590 The data from the oFFs chunk can be retrieved in several convenient
1593 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1594 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1595 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1596 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1598 (Each of these returns 0 [signifying "unknown" if both
1599 x and y are 0] if the data is not present or if the
1600 chunk is present but the unit is the pixel)
1602 For more information, see the png_info definition in png.h and the
1603 PNG specification for chunk contents. Be careful with trusting
1604 rowbytes, as some of the transformations could increase the space
1605 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1606 See png_read_update_info(), below.
1608 A quick word about text_ptr and num_text. PNG stores comments in
1609 keyword/text pairs, one pair per chunk, with no limit on the number
1610 of text chunks, and a 2^31 byte limit on their size. While there are
1611 suggested keywords, there is no requirement to restrict the use to these
1612 strings. It is strongly suggested that keywords and text be sensible
1613 to humans (that's the point), so don't use abbreviations. Non-printing
1614 symbols are not allowed. See the PNG specification for more details.
1615 There is also no requirement to have text after the keyword.
1617 Keywords should be limited to 79 Latin-1 characters without leading or
1618 trailing spaces, but non-consecutive spaces are allowed within the
1619 keyword. It is possible to have the same keyword any number of times.
1620 The text_ptr is an array of png_text structures, each holding a
1621 pointer to a language string, a pointer to a keyword and a pointer to
1622 a text string. The text string, language code, and translated
1623 keyword may be empty or NULL pointers. The keyword/text
1624 pairs are put into the array in the order that they are received.
1625 However, some or all of the text chunks may be after the image, so, to
1626 make sure you have read all the text chunks, don't mess with these
1627 until after you read the stuff after the image. This will be
1628 mentioned again below in the discussion that goes with png_read_end().
1630 .SS Input transformations
1632 After you've read the header information, you can set up the library
1633 to handle any special transformations of the image data. The various
1634 ways to transform the data will be described in the order that they
1635 should occur. This is important, as some of these change the color
1636 type and/or bit depth of the data, and some others only work on
1637 certain color types and bit depths. Even though each transformation
1638 checks to see if it has data that it can do something with, you should
1639 make sure to only enable a transformation if it will be valid for the
1640 data. For example, don't swap red and blue on grayscale data.
1642 The colors used for the background and transparency values should be
1643 supplied in the same format/depth as the current image data. They
1644 are stored in the same format/depth as the image data in a bKGD or tRNS
1645 chunk, so this is what libpng expects for this data. The colors are
1646 transformed to keep in sync with the image data when an application
1647 calls the png_read_update_info() routine (see below).
1649 Data will be decoded into the supplied row buffers packed into bytes
1650 unless the library has been told to transform it into another format.
1651 For example, 4 bit/pixel paletted or grayscale data will be returned
1652 2 pixels/byte with the leftmost pixel in the high-order bits of the
1653 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1654 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1655 is called to insert filler bytes, either before or after each RGB triplet.
1656 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1657 byte of the color value first, unless png_set_strip_16() is called to
1658 transform it to regular RGB RGB triplets, or png_set_filler() or
1659 png_set_add alpha() is called to insert filler bytes, either before or
1660 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1662 png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1664 The following code transforms grayscale images of less than 8 to 8 bits,
1665 changes paletted images to RGB, and adds a full alpha channel if there is
1666 transparency information in a tRNS chunk. This is most useful on
1667 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1668 viewing application that wishes to treat all images in the same way.
1670 if (color_type == PNG_COLOR_TYPE_PALETTE)
1671 png_set_palette_to_rgb(png_ptr);
1673 if (color_type == PNG_COLOR_TYPE_GRAY &&
1674 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1676 if (png_get_valid(png_ptr, info_ptr,
1677 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1679 These three functions are actually aliases for png_set_expand(), added
1680 in libpng version 1.0.4, with the function names expanded to improve code
1681 readability. In some future version they may actually do different
1684 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1685 added. It expands the sample depth without changing tRNS to alpha.
1687 As of libpng version 1.4.1, not all possible expansions are supported.
1689 In the following table, the 01 means grayscale with depth<8, 31 means
1690 indexed with depth<8, other numerals represent the color type, "T" means
1691 the tRNS chunk is present, A means an alpha channel is present, and O
1692 means tRNS or alpha is present but all pixels in the image are opaque.
1694 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
1713 "-" means the transformation is not supported.
1714 "X" means the transformation is obtained by png_set_expand().
1715 "1" means the transformation is obtained by
1716 png_set_expand_gray_1_2_4_to_8
1717 "G" means the transformation is obtained by
1718 png_set_gray_to_rgb().
1719 "P" means the transformation is obtained by
1720 png_set_expand_palette_to_rgb().
1721 "T" means the transformation is obtained by
1722 png_set_tRNS_to_alpha().
1724 PNG can have files with 16 bits per channel. If you only can handle
1725 8 bits per channel, this will strip the pixels down to 8 bit.
1727 if (bit_depth == 16)
1728 png_set_strip_16(png_ptr);
1730 If, for some reason, you don't need the alpha channel on an image,
1731 and you want to remove it rather than combining it with the background
1732 (but the image author certainly had in mind that you *would* combine
1733 it with the background, so that's what you should probably do):
1735 if (color_type & PNG_COLOR_MASK_ALPHA)
1736 png_set_strip_alpha(png_ptr);
1738 In PNG files, the alpha channel in an image
1739 is the level of opacity. If you need the alpha channel in an image to
1740 be the level of transparency instead of opacity, you can invert the
1741 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1742 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1743 images) is fully transparent, with
1745 png_set_invert_alpha(png_ptr);
1747 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1748 they can, resulting in, for example, 8 pixels per byte for 1 bit
1749 files. This code expands to 1 pixel per byte without changing the
1750 values of the pixels:
1753 png_set_packing(png_ptr);
1755 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1756 stored in a PNG image have been "scaled" or "shifted" up to the next
1757 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
1758 to 8 bits/sample in the range [0, 255]). However, it is also possible
1759 to convert the PNG pixel data back to the original bit depth of the
1760 image. This call reduces the pixels back down to the original bit depth:
1762 png_color_8p sig_bit;
1764 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1765 png_set_shift(png_ptr, sig_bit);
1767 PNG files store 3-color pixels in red, green, blue order. This code
1768 changes the storage of the pixels to blue, green, red:
1770 if (color_type == PNG_COLOR_TYPE_RGB ||
1771 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1772 png_set_bgr(png_ptr);
1774 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1775 into 4 or 8 bytes for windowing systems that need them in this format:
1777 if (color_type == PNG_COLOR_TYPE_RGB)
1778 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1780 where "filler" is the 8 or 16-bit number to fill with, and the location is
1781 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1782 you want the filler before the RGB or after. This transformation
1783 does not affect images that already have full alpha channels. To add an
1784 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1785 will generate RGBA pixels.
1787 Note that png_set_filler() does not change the color type. If you want
1788 to do that, you can add a true alpha channel with
1790 if (color_type == PNG_COLOR_TYPE_RGB ||
1791 color_type == PNG_COLOR_TYPE_GRAY)
1792 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1794 where "filler" contains the alpha value to assign to each pixel.
1795 This function was added in libpng-1.2.7.
1797 If you are reading an image with an alpha channel, and you need the
1798 data as ARGB instead of the normal PNG format RGBA:
1800 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1801 png_set_swap_alpha(png_ptr);
1803 For some uses, you may want a grayscale image to be represented as
1804 RGB. This code will do that conversion:
1806 if (color_type == PNG_COLOR_TYPE_GRAY ||
1807 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1808 png_set_gray_to_rgb(png_ptr);
1810 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1813 if (color_type == PNG_COLOR_TYPE_RGB ||
1814 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1815 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1816 int red_weight, int green_weight);
1818 error_action = 1: silently do the conversion
1819 error_action = 2: issue a warning if the original
1820 image has any pixel where
1821 red != green or red != blue
1822 error_action = 3: issue an error and abort the
1823 conversion if the original
1824 image has any pixel where
1825 red != green or red != blue
1827 red_weight: weight of red component times 100000
1828 green_weight: weight of green component times 100000
1829 If either weight is negative, default
1830 weights (21268, 71514) are used.
1832 If you have set error_action = 1 or 2, you can
1833 later check whether the image really was gray, after processing
1834 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1835 It will return a png_byte that is zero if the image was gray or
1836 1 if there were any non-gray pixels. bKGD and sBIT data
1837 will be silently converted to grayscale, using the green channel
1838 data, regardless of the error_action setting.
1840 With red_weight+green_weight<=100000,
1841 the normalized graylevel is computed:
1843 int rw = red_weight * 65536;
1844 int gw = green_weight * 65536;
1845 int bw = 65536 - (rw + gw);
1846 gray = (rw*red + gw*green + bw*blue)/65536;
1848 The default values approximate those recommended in the Charles
1849 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1850 Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1852 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1854 Libpng approximates this with
1856 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1858 which can be expressed with integers as
1860 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1862 The calculation is done in a linear colorspace, if the image gamma
1865 If you have a grayscale and you are using png_set_expand_depth(),
1866 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1867 a higher bit-depth, you must either supply the background color as a gray
1868 value at the original file bit-depth (need_expand = 1) or else supply the
1869 background color as an RGB triplet at the final, expanded bit depth
1870 (need_expand = 0). Similarly, if you are reading a paletted image, you
1871 must either supply the background color as a palette index (need_expand = 1)
1872 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1874 png_color_16 my_background;
1875 png_color_16p image_background;
1877 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1878 png_set_background(png_ptr, image_background,
1879 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1881 png_set_background(png_ptr, &my_background,
1882 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1884 The png_set_background() function tells libpng to composite images
1885 with alpha or simple transparency against the supplied background
1886 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1887 you may use this color, or supply another color more suitable for
1888 the current display (e.g., the background color from a web page). You
1889 need to tell libpng whether the color is in the gamma space of the
1890 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1891 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1892 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1893 know why anyone would use this, but it's here).
1895 To properly display PNG images on any kind of system, the application needs
1896 to know what the display gamma is. Ideally, the user will know this, and
1897 the application will allow them to set it. One method of allowing the user
1898 to set the display gamma separately for each system is to check for a
1899 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1902 Note that display_gamma is the overall gamma correction required to produce
1903 pleasing results, which depends on the lighting conditions in the surrounding
1904 environment. In a dim or brightly lit room, no compensation other than
1905 the physical gamma exponent of the monitor is needed, while in a dark room
1906 a slightly smaller exponent is better.
1908 double gamma, screen_gamma;
1910 if (/* We have a user-defined screen
1913 screen_gamma = user_defined_screen_gamma;
1915 /* One way that applications can share the same
1916 screen gamma value */
1917 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1920 screen_gamma = (double)atof(gamma_str);
1922 /* If we don't have another value */
1925 screen_gamma = 2.2; /* A good guess for a
1926 PC monitor in a bright office or a dim room */
1927 screen_gamma = 2.0; /* A good guess for a
1928 PC monitor in a dark room */
1929 screen_gamma = 1.7 or 1.0; /* A good
1930 guess for Mac systems */
1933 The png_set_gamma() function handles gamma transformations of the data.
1934 Pass both the file gamma and the current screen_gamma. If the file does
1935 not have a gamma value, you can pass one anyway if you have an idea what
1936 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1937 that file gammas are inverted from screen gammas. See the discussions
1938 on gamma in the PNG specification for an excellent description of what
1939 gamma is, and why all applications should support it. It is strongly
1940 recommended that PNG viewers support gamma correction.
1942 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1943 png_set_gamma(png_ptr, screen_gamma, gamma);
1945 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1947 PNG files describe monochrome as black being zero and white being one.
1948 The following code will reverse this (make black be one and white be
1951 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1952 png_set_invert_mono(png_ptr);
1954 This function can also be used to invert grayscale and gray-alpha images:
1956 if (color_type == PNG_COLOR_TYPE_GRAY ||
1957 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1958 png_set_invert_mono(png_ptr);
1960 PNG files store 16 bit pixels in network byte order (big-endian,
1961 ie. most significant bits first). This code changes the storage to the
1962 other way (little-endian, i.e. least significant bits first, the
1963 way PCs store them):
1965 if (bit_depth == 16)
1966 png_set_swap(png_ptr);
1968 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1969 need to change the order the pixels are packed into bytes, you can use:
1972 png_set_packswap(png_ptr);
1974 Finally, you can write your own transformation function if none of
1975 the existing ones meets your needs. This is done by setting a callback
1978 png_set_read_user_transform_fn(png_ptr,
1981 You must supply the function
1983 void read_transform_fn(png_ptr ptr, row_info_ptr
1984 row_info, png_bytep data)
1986 See pngtest.c for a working example. Your function will be called
1987 after all of the other transformations have been processed.
1989 You can also set up a pointer to a user structure for use by your
1990 callback function, and you can inform libpng that your transform
1991 function will change the number of channels or bit depth with the
1994 png_set_user_transform_info(png_ptr, user_ptr,
1995 user_depth, user_channels);
1997 The user's application, not libpng, is responsible for allocating and
1998 freeing any memory required for the user structure.
2000 You can retrieve the pointer via the function
2001 png_get_user_transform_ptr(). For example:
2003 voidp read_user_transform_ptr =
2004 png_get_user_transform_ptr(png_ptr);
2006 The last thing to handle is interlacing; this is covered in detail below,
2007 but you must call the function here if you want libpng to handle expansion
2008 of the interlaced image.
2010 number_of_passes = png_set_interlace_handling(png_ptr);
2012 After setting the transformations, libpng can update your png_info
2013 structure to reflect any transformations you've requested with this
2014 call. This is most useful to update the info structure's rowbytes
2015 field so you can use it to allocate your image memory. This function
2016 will also update your palette with the correct screen_gamma and
2017 background if these have been given with the calls above.
2019 png_read_update_info(png_ptr, info_ptr);
2021 After you call png_read_update_info(), you can allocate any
2022 memory you need to hold the image. The row data is simply
2023 raw byte data for all forms of images. As the actual allocation
2024 varies among applications, no example will be given. If you
2025 are allocating one large chunk, you will need to build an
2026 array of pointers to each row, as it will be needed for some
2027 of the functions below.
2029 .SS Reading image data
2031 After you've allocated memory, you can read the image data.
2032 The simplest way to do this is in one function call. If you are
2033 allocating enough memory to hold the whole image, you can just
2034 call png_read_image() and libpng will read in all the image data
2035 and put it in the memory area supplied. You will need to pass in
2036 an array of pointers to each row.
2038 This function automatically handles interlacing, so you don't need
2039 to call png_set_interlace_handling() or call this function multiple
2040 times, or any of that other stuff necessary with png_read_rows().
2042 png_read_image(png_ptr, row_pointers);
2044 where row_pointers is:
2046 png_bytep row_pointers[height];
2048 You can point to void or char or whatever you use for pixels.
2050 If you don't want to read in the whole image at once, you can
2051 use png_read_rows() instead. If there is no interlacing (check
2052 interlace_type == PNG_INTERLACE_NONE), this is simple:
2054 png_read_rows(png_ptr, row_pointers, NULL,
2057 where row_pointers is the same as in the png_read_image() call.
2059 If you are doing this just one row at a time, you can do this with
2060 a single row_pointer instead of an array of row_pointers:
2062 png_bytep row_pointer = row;
2063 png_read_row(png_ptr, row_pointer, NULL);
2065 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2066 get somewhat harder. The only current (PNG Specification version 1.2)
2067 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
2068 is a somewhat complicated 2D interlace scheme, known as Adam7, that
2069 breaks down an image into seven smaller images of varying size, based
2072 libpng can fill out those images or it can give them to you "as is".
2073 If you want them filled out, there are two ways to do that. The one
2074 mentioned in the PNG specification is to expand each pixel to cover
2075 those pixels that have not been read yet (the "rectangle" method).
2076 This results in a blocky image for the first pass, which gradually
2077 smooths out as more pixels are read. The other method is the "sparkle"
2078 method, where pixels are drawn only in their final locations, with the
2079 rest of the image remaining whatever colors they were initialized to
2080 before the start of the read. The first method usually looks better,
2081 but tends to be slower, as there are more pixels to put in the rows.
2083 If you don't want libpng to handle the interlacing details, just call
2084 png_read_rows() seven times to read in all seven images. Each of the
2085 images is a valid image by itself, or they can all be combined on an
2086 8x8 grid to form a single image (although if you intend to combine them
2087 you would be far better off using the libpng interlace handling).
2089 The first pass will return an image 1/8 as wide as the entire image
2090 (every 8th column starting in column 0) and 1/8 as high as the original
2091 (every 8th row starting in row 0), the second will be 1/8 as wide
2092 (starting in column 4) and 1/8 as high (also starting in row 0). The
2093 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
2094 1/8 as high (every 8th row starting in row 4), and the fourth pass will
2095 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
2096 and every 4th row starting in row 0). The fifth pass will return an
2097 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
2098 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
2099 (starting in column 1 and row 0). The seventh and final pass will be as
2100 wide as the original, and 1/2 as high, containing all of the odd
2101 numbered scanlines. Phew!
2103 If you want libpng to expand the images, call this before calling
2104 png_start_read_image() or png_read_update_info():
2106 if (interlace_type == PNG_INTERLACE_ADAM7)
2108 = png_set_interlace_handling(png_ptr);
2110 This will return the number of passes needed. Currently, this
2111 is seven, but may change if another interlace type is added.
2112 This function can be called even if the file is not interlaced,
2113 where it will return one pass.
2115 If you are not going to display the image after each pass, but are
2116 going to wait until the entire image is read in, use the sparkle
2117 effect. This effect is faster and the end result of either method
2118 is exactly the same. If you are planning on displaying the image
2119 after each pass, the "rectangle" effect is generally considered the
2122 If you only want the "sparkle" effect, just call png_read_rows() as
2123 normal, with the third parameter NULL. Make sure you make pass over
2124 the image number_of_passes times, and you don't change the data in the
2125 rows between calls. You can change the locations of the data, just
2126 not the data. Each pass only writes the pixels appropriate for that
2127 pass, and assumes the data from previous passes is still valid.
2129 png_read_rows(png_ptr, row_pointers, NULL,
2132 If you only want the first effect (the rectangles), do the same as
2133 before except pass the row buffer in the third parameter, and leave
2134 the second parameter NULL.
2136 png_read_rows(png_ptr, NULL, row_pointers,
2139 .SS Finishing a sequential read
2141 After you are finished reading the image through the
2142 low-level interface, you can finish reading the file. If you are
2143 interested in comments or time, which may be stored either before or
2144 after the image data, you should pass the separate png_info struct if
2145 you want to keep the comments from before and after the image
2146 separate. If you are not interested, you can pass NULL.
2148 png_read_end(png_ptr, end_info);
2150 When you are done, you can free all memory allocated by libpng like this:
2152 png_destroy_read_struct(&png_ptr, &info_ptr,
2155 It is also possible to individually free the info_ptr members that
2156 point to libpng-allocated storage with the following function:
2158 png_free_data(png_ptr, info_ptr, mask, seq)
2159 mask - identifies data to be freed, a mask
2160 containing the bitwise OR of one or
2162 PNG_FREE_PLTE, PNG_FREE_TRNS,
2163 PNG_FREE_HIST, PNG_FREE_ICCP,
2164 PNG_FREE_PCAL, PNG_FREE_ROWS,
2165 PNG_FREE_SCAL, PNG_FREE_SPLT,
2166 PNG_FREE_TEXT, PNG_FREE_UNKN,
2167 or simply PNG_FREE_ALL
2168 seq - sequence number of item to be freed
2171 This function may be safely called when the relevant storage has
2172 already been freed, or has not yet been allocated, or was allocated
2173 by the user and not by libpng, and will in those cases do nothing.
2174 The "seq" parameter is ignored if only one item of the selected data
2175 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
2176 are allowed for the data type identified in the mask, such as text or
2177 sPLT, only the n'th item in the structure is freed, where n is "seq".
2179 The default behavior is only to free data that was allocated internally
2180 by libpng. This can be changed, so that libpng will not free the data,
2181 or so that it will free data that was allocated by the user with png_malloc()
2182 or png_zalloc() and passed in via a png_set_*() function, with
2184 png_data_freer(png_ptr, info_ptr, freer, mask)
2185 mask - which data elements are affected
2186 same choices as in png_free_data()
2188 PNG_DESTROY_WILL_FREE_DATA
2189 PNG_SET_WILL_FREE_DATA
2190 PNG_USER_WILL_FREE_DATA
2192 This function only affects data that has already been allocated.
2193 You can call this function after reading the PNG data but before calling
2194 any png_set_*() functions, to control whether the user or the png_set_*()
2195 function is responsible for freeing any existing data that might be present,
2196 and again after the png_set_*() functions to control whether the user
2197 or png_destroy_*() is supposed to free the data. When the user assumes
2198 responsibility for libpng-allocated data, the application must use
2199 png_free() to free it, and when the user transfers responsibility to libpng
2200 for data that the user has allocated, the user must have used png_malloc()
2201 or png_zalloc() to allocate it.
2203 If you allocated your row_pointers in a single block, as suggested above in
2204 the description of the high level read interface, you must not transfer
2205 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2206 because they would also try to free the individual row_pointers[i].
2208 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2209 separately, do not transfer responsibility for freeing text_ptr to libpng,
2210 because when libpng fills a png_text structure it combines these members with
2211 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2212 if you transfer responsibility for free'ing text_ptr from libpng to your
2213 application, your application must not separately free those members.
2215 The png_free_data() function will turn off the "valid" flag for anything
2216 it frees. If you need to turn the flag off for a chunk that was freed by
2217 your application instead of by libpng, you can use
2219 png_set_invalid(png_ptr, info_ptr, mask);
2220 mask - identifies the chunks to be made invalid,
2221 containing the bitwise OR of one or
2223 PNG_INFO_gAMA, PNG_INFO_sBIT,
2224 PNG_INFO_cHRM, PNG_INFO_PLTE,
2225 PNG_INFO_tRNS, PNG_INFO_bKGD,
2226 PNG_INFO_hIST, PNG_INFO_pHYs,
2227 PNG_INFO_oFFs, PNG_INFO_tIME,
2228 PNG_INFO_pCAL, PNG_INFO_sRGB,
2229 PNG_INFO_iCCP, PNG_INFO_sPLT,
2230 PNG_INFO_sCAL, PNG_INFO_IDAT
2232 For a more compact example of reading a PNG image, see the file example.c.
2234 .SS Reading PNG files progressively
2236 The progressive reader is slightly different then the non-progressive
2237 reader. Instead of calling png_read_info(), png_read_rows(), and
2238 png_read_end(), you make one call to png_process_data(), which calls
2239 callbacks when it has the info, a row, or the end of the image. You
2240 set up these callbacks with png_set_progressive_read_fn(). You don't
2241 have to worry about the input/output functions of libpng, as you are
2242 giving the library the data directly in png_process_data(). I will
2243 assume that you have read the section on reading PNG files above,
2244 so I will only highlight the differences (although I will show
2247 png_structp png_ptr;
2250 /* An example code fragment of how you would
2251 initialize the progressive reader in your
2254 initialize_png_reader()
2256 png_ptr = png_create_read_struct
2257 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2258 user_error_fn, user_warning_fn);
2261 info_ptr = png_create_info_struct(png_ptr);
2264 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2269 if (setjmp(png_jmpbuf(png_ptr)))
2271 png_destroy_read_struct(&png_ptr, &info_ptr,
2276 /* This one's new. You can provide functions
2277 to be called when the header info is valid,
2278 when each row is completed, and when the image
2279 is finished. If you aren't using all functions,
2280 you can specify NULL parameters. Even when all
2281 three functions are NULL, you need to call
2282 png_set_progressive_read_fn(). You can use
2283 any struct as the user_ptr (cast to a void pointer
2284 for the function call), and retrieve the pointer
2285 from inside the callbacks using the function
2287 png_get_progressive_ptr(png_ptr);
2289 which will return a void pointer, which you have
2290 to cast appropriately.
2292 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2293 info_callback, row_callback, end_callback);
2298 /* A code fragment that you call as you receive blocks
2301 process_data(png_bytep buffer, png_uint_32 length)
2303 if (setjmp(png_jmpbuf(png_ptr)))
2305 png_destroy_read_struct(&png_ptr, &info_ptr,
2310 /* This one's new also. Simply give it a chunk
2311 of data from the file stream (in order, of
2312 course). On machines with segmented memory
2313 models machines, don't give it any more than
2314 64K. The library seems to run fine with sizes
2315 of 4K. Although you can give it much less if
2316 necessary (I assume you can give it chunks of
2317 1 byte, I haven't tried less then 256 bytes
2318 yet). When this function returns, you may
2319 want to display any rows that were generated
2320 in the row callback if you don't already do
2323 png_process_data(png_ptr, info_ptr, buffer, length);
2327 /* This function is called (as set by
2328 png_set_progressive_read_fn() above) when enough data
2329 has been supplied so all of the header has been
2333 info_callback(png_structp png_ptr, png_infop info)
2335 /* Do any setup here, including setting any of
2336 the transformations mentioned in the Reading
2337 PNG files section. For now, you _must_ call
2338 either png_start_read_image() or
2339 png_read_update_info() after all the
2340 transformations are set (even if you don't set
2341 any). You may start getting rows before
2342 png_process_data() returns, so this is your
2343 last chance to prepare for that.
2347 /* This function is called when each row of image
2350 row_callback(png_structp png_ptr, png_bytep new_row,
2351 png_uint_32 row_num, int pass)
2353 /* If the image is interlaced, and you turned
2354 on the interlace handler, this function will
2355 be called for every row in every pass. Some
2356 of these rows will not be changed from the
2357 previous pass. When the row is not changed,
2358 the new_row variable will be NULL. The rows
2359 and passes are called in order, so you don't
2360 really need the row_num and pass, but I'm
2361 supplying them because it may make your life
2364 For the non-NULL rows of interlaced images,
2365 you must call png_progressive_combine_row()
2366 passing in the row and the old row. You can
2367 call this function for NULL rows (it will just
2368 return) and for non-interlaced images (it just
2369 does the memcpy for you) if it will make the
2370 code easier. Thus, you can just do this for
2374 png_progressive_combine_row(png_ptr, old_row,
2377 /* where old_row is what was displayed for
2378 previously for the row. Note that the first
2379 pass (pass == 0, really) will completely cover
2380 the old row, so the rows do not have to be
2381 initialized. After the first pass (and only
2382 for interlaced images), you will have to pass
2383 the current row, and the function will combine
2384 the old row and the new row.
2389 end_callback(png_structp png_ptr, png_infop info)
2391 /* This function is called after the whole image
2392 has been read, including any chunks after the
2393 image (up to and including the IEND). You
2394 will usually have the same info chunk as you
2395 had in the header, although some data may have
2396 been added to the comments and time fields.
2398 Most people won't do much here, perhaps setting
2399 a flag that marks the image as finished.
2407 Much of this is very similar to reading. However, everything of
2408 importance is repeated here, so you won't have to constantly look
2409 back up in the reading section to understand writing.
2413 You will want to do the I/O initialization before you get into libpng,
2414 so if it doesn't work, you don't have anything to undo. If you are not
2415 using the standard I/O functions, you will need to replace them with
2416 custom writing functions. See the discussion under Customizing libpng.
2418 FILE *fp = fopen(file_name, "wb");
2424 Next, png_struct and png_info need to be allocated and initialized.
2425 As these can be both relatively large, you may not want to store these
2426 on the stack, unless you have stack space to spare. Of course, you
2427 will want to check if they return NULL. If you are also reading,
2428 you won't want to name your read structure and your write structure
2429 both "png_ptr"; you can call them anything you like, such as
2430 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2432 png_structp png_ptr = png_create_write_struct
2433 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2434 user_error_fn, user_warning_fn);
2438 png_infop info_ptr = png_create_info_struct(png_ptr);
2441 png_destroy_write_struct(&png_ptr,
2446 If you want to use your own memory allocation routines,
2447 define PNG_USER_MEM_SUPPORTED and use
2448 png_create_write_struct_2() instead of png_create_write_struct():
2450 png_structp png_ptr = png_create_write_struct_2
2451 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2452 user_error_fn, user_warning_fn, (png_voidp)
2453 user_mem_ptr, user_malloc_fn, user_free_fn);
2455 After you have these structures, you will need to set up the
2456 error handling. When libpng encounters an error, it expects to
2457 longjmp() back to your routine. Therefore, you will need to call
2458 setjmp() and pass the png_jmpbuf(png_ptr). If you
2459 write the file from different routines, you will need to update
2460 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2461 call a png_*() function. See your documentation of setjmp/longjmp
2462 for your compiler for more information on setjmp/longjmp. See
2463 the discussion on libpng error handling in the Customizing Libpng
2464 section below for more information on the libpng error handling.
2466 if (setjmp(png_jmpbuf(png_ptr)))
2468 png_destroy_write_struct(&png_ptr, &info_ptr);
2475 If you would rather avoid the complexity of setjmp/longjmp issues,
2476 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2477 errors will result in a call to PNG_ABORT() which defaults to abort().
2479 Now you need to set up the output code. The default for libpng is to
2480 use the C function fwrite(). If you use this, you will need to pass a
2481 valid FILE * in the function png_init_io(). Be sure that the file is
2482 opened in binary mode. Again, if you wish to handle writing data in
2483 another way, see the discussion on libpng I/O handling in the Customizing
2484 Libpng section below.
2486 png_init_io(png_ptr, fp);
2488 If you are embedding your PNG into a datastream such as MNG, and don't
2489 want libpng to write the 8-byte signature, or if you have already
2490 written the signature in your application, use
2492 png_set_sig_bytes(png_ptr, 8);
2494 to inform libpng that it should not write a signature.
2498 At this point, you can set up a callback function that will be
2499 called after each row has been written, which you can use to control
2500 a progress meter or the like. It's demonstrated in pngtest.c.
2501 You must supply a function
2503 void write_row_callback(png_ptr, png_uint_32 row,
2506 /* put your code here */
2509 (You can give it another name that you like instead of "write_row_callback")
2511 To inform libpng about your function, use
2513 png_set_write_status_fn(png_ptr, write_row_callback);
2515 You now have the option of modifying how the compression library will
2516 run. The following functions are mainly for testing, but may be useful
2517 in some cases, like if you need to write PNG files extremely fast and
2518 are willing to give up some compression, or if you want to get the
2519 maximum possible compression at the expense of slower writing. If you
2520 have no special needs in this area, let the library do what it wants by
2521 not calling this function at all, as it has been tuned to deliver a good
2522 speed/compression ratio. The second parameter to png_set_filter() is
2523 the filter method, for which the only valid values are 0 (as of the
2524 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2525 a PNG datastream that is to be embedded in a MNG datastream). The third
2526 parameter is a flag that indicates which filter type(s) are to be tested
2527 for each scanline. See the PNG specification for details on the specific
2531 /* turn on or off filtering, and/or choose
2532 specific filters. You can use either a single
2533 PNG_FILTER_VALUE_NAME or the bitwise OR of one
2534 or more PNG_FILTER_NAME masks. */
2535 png_set_filter(png_ptr, 0,
2536 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2537 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2538 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2539 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
2540 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2544 wants to start and stop using particular filters during compression,
2545 it should start out with all of the filters (to ensure that the previous
2546 row of pixels will be stored in case it's needed later), and then add
2547 and remove them after the start of compression.
2549 If you are writing a PNG datastream that is to be embedded in a MNG
2550 datastream, the second parameter can be either 0 or 64.
2552 The png_set_compression_*() functions interface to the zlib compression
2553 library, and should mostly be ignored unless you really know what you are
2554 doing. The only generally useful call is png_set_compression_level()
2555 which changes how much time zlib spends on trying to compress the image
2556 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2557 with zlib) for details on the compression levels.
2559 /* set the zlib compression level */
2560 png_set_compression_level(png_ptr,
2561 Z_BEST_COMPRESSION);
2563 /* set other zlib parameters */
2564 png_set_compression_mem_level(png_ptr, 8);
2565 png_set_compression_strategy(png_ptr,
2566 Z_DEFAULT_STRATEGY);
2567 png_set_compression_window_bits(png_ptr, 15);
2568 png_set_compression_method(png_ptr, 8);
2569 png_set_compression_buffer_size(png_ptr, 8192)
2571 extern PNG_EXPORT(void,png_set_zbuf_size)
2573 .SS Setting the contents of info for output
2575 You now need to fill in the png_info structure with all the data you
2576 wish to write before the actual image. Note that the only thing you
2577 are allowed to write after the image is the text chunks and the time
2578 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2579 the latest PNG specification for more information on that. If you
2580 wish to write them before the image, fill them in now, and flag that
2581 data as being valid. If you want to wait until after the data, don't
2582 fill them until png_write_end(). For all the fields in png_info and
2583 their data types, see png.h. For explanations of what the fields
2584 contain, see the PNG specification.
2586 Some of the more important parts of the png_info are:
2588 png_set_IHDR(png_ptr, info_ptr, width, height,
2589 bit_depth, color_type, interlace_type,
2590 compression_type, filter_method)
2591 width - holds the width of the image
2592 in pixels (up to 2^31).
2593 height - holds the height of the image
2594 in pixels (up to 2^31).
2595 bit_depth - holds the bit depth of one of the
2597 (valid values are 1, 2, 4, 8, 16
2598 and depend also on the
2599 color_type. See also significant
2601 color_type - describes which color/alpha
2602 channels are present.
2604 (bit depths 1, 2, 4, 8, 16)
2605 PNG_COLOR_TYPE_GRAY_ALPHA
2607 PNG_COLOR_TYPE_PALETTE
2608 (bit depths 1, 2, 4, 8)
2611 PNG_COLOR_TYPE_RGB_ALPHA
2614 PNG_COLOR_MASK_PALETTE
2615 PNG_COLOR_MASK_COLOR
2616 PNG_COLOR_MASK_ALPHA
2618 interlace_type - PNG_INTERLACE_NONE or
2620 compression_type - (must be
2621 PNG_COMPRESSION_TYPE_DEFAULT)
2622 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2623 or, if you are writing a PNG to
2624 be embedded in a MNG datastream,
2626 PNG_INTRAPIXEL_DIFFERENCING)
2628 If you call png_set_IHDR(), the call must appear before any of the
2629 other png_set_*() functions, because they might require access to some of
2630 the IHDR settings. The remaining png_set_*() functions can be called
2633 If you wish, you can reset the compression_type, interlace_type, or
2634 filter_method later by calling png_set_IHDR() again; if you do this, the
2635 width, height, bit_depth, and color_type must be the same in each call.
2637 png_set_PLTE(png_ptr, info_ptr, palette,
2639 palette - the palette for the file
2640 (array of png_color)
2641 num_palette - number of entries in the palette
2643 png_set_gAMA(png_ptr, info_ptr, gamma);
2644 gamma - the gamma the image was created
2647 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2648 srgb_intent - the rendering intent
2649 (PNG_INFO_sRGB) The presence of
2650 the sRGB chunk means that the pixel
2651 data is in the sRGB color space.
2652 This chunk also implies specific
2653 values of gAMA and cHRM. Rendering
2654 intent is the CSS-1 property that
2655 has been defined by the International
2657 (http://www.color.org).
2659 PNG_sRGB_INTENT_SATURATION,
2660 PNG_sRGB_INTENT_PERCEPTUAL,
2661 PNG_sRGB_INTENT_ABSOLUTE, or
2662 PNG_sRGB_INTENT_RELATIVE.
2665 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2667 srgb_intent - the rendering intent
2668 (PNG_INFO_sRGB) The presence of the
2669 sRGB chunk means that the pixel
2670 data is in the sRGB color space.
2671 This function also causes gAMA and
2672 cHRM chunks with the specific values
2673 that are consistent with sRGB to be
2676 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2678 name - The profile name.
2679 compression - The compression type; always
2680 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2681 You may give NULL to this argument to
2683 profile - International Color Consortium color
2684 profile data. May contain NULs.
2685 proflen - length of profile data in bytes.
2687 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2688 sig_bit - the number of significant bits for
2689 (PNG_INFO_sBIT) each of the gray, red,
2690 green, and blue channels, whichever are
2691 appropriate for the given color type
2694 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
2695 num_trans, trans_color);
2696 trans_alpha - array of alpha (transparency)
2697 entries for palette (PNG_INFO_tRNS)
2698 trans_color - graylevel or color sample values
2699 (in order red, green, blue) of the
2700 single transparent color for
2701 non-paletted images (PNG_INFO_tRNS)
2702 num_trans - number of transparent entries
2705 png_set_hIST(png_ptr, info_ptr, hist);
2707 hist - histogram of palette (array of
2710 png_set_tIME(png_ptr, info_ptr, mod_time);
2711 mod_time - time image was last modified
2714 png_set_bKGD(png_ptr, info_ptr, background);
2715 background - background color (PNG_VALID_bKGD)
2717 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2718 text_ptr - array of png_text holding image
2720 text_ptr[i].compression - type of compression used
2721 on "text" PNG_TEXT_COMPRESSION_NONE
2722 PNG_TEXT_COMPRESSION_zTXt
2723 PNG_ITXT_COMPRESSION_NONE
2724 PNG_ITXT_COMPRESSION_zTXt
2725 text_ptr[i].key - keyword for comment. Must contain
2727 text_ptr[i].text - text comments for current
2728 keyword. Can be NULL or empty.
2729 text_ptr[i].text_length - length of text string,
2730 after decompression, 0 for iTXt
2731 text_ptr[i].itxt_length - length of itxt string,
2732 after decompression, 0 for tEXt/zTXt
2733 text_ptr[i].lang - language of comment (NULL or
2735 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2736 or empty for unknown).
2737 Note that the itxt_length, lang, and lang_key
2738 members of the text_ptr structure only exist
2739 when the library is built with iTXt chunk support.
2741 num_text - number of comments
2743 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2745 palette_ptr - array of png_sPLT_struct structures
2746 to be added to the list of palettes
2747 in the info structure.
2748 num_spalettes - number of palette structures to be
2751 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2753 offset_x - positive offset from the left
2755 offset_y - positive offset from the top
2757 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2759 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2761 res_x - pixels/unit physical resolution
2763 res_y - pixels/unit physical resolution
2765 unit_type - PNG_RESOLUTION_UNKNOWN,
2766 PNG_RESOLUTION_METER
2768 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2769 unit - physical scale units (an integer)
2770 width - width of a pixel in physical scale units
2771 height - height of a pixel in physical scale units
2772 (width and height are doubles)
2774 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2775 unit - physical scale units (an integer)
2776 width - width of a pixel in physical scale units
2777 height - height of a pixel in physical scale units
2778 (width and height are strings like "2.54")
2780 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2782 unknowns - array of png_unknown_chunk
2783 structures holding unknown chunks
2784 unknowns[i].name - name of unknown chunk
2785 unknowns[i].data - data of unknown chunk
2786 unknowns[i].size - size of unknown chunk's data
2787 unknowns[i].location - position to write chunk in file
2788 0: do not write chunk
2789 PNG_HAVE_IHDR: before PLTE
2790 PNG_HAVE_PLTE: before IDAT
2791 PNG_AFTER_IDAT: after IDAT
2793 The "location" member is set automatically according to
2794 what part of the output file has already been written.
2795 You can change its value after calling png_set_unknown_chunks()
2796 as demonstrated in pngtest.c. Within each of the "locations",
2797 the chunks are sequenced according to their position in the
2798 structure (that is, the value of "i", which is the order in which
2799 the chunk was either read from the input file or defined with
2800 png_set_unknown_chunks).
2802 A quick word about text and num_text. text is an array of png_text
2803 structures. num_text is the number of valid structures in the array.
2804 Each png_text structure holds a language code, a keyword, a text value,
2805 and a compression type.
2807 The compression types have the same valid numbers as the compression
2808 types of the image data. Currently, the only valid number is zero.
2809 However, you can store text either compressed or uncompressed, unlike
2810 images, which always have to be compressed. So if you don't want the
2811 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2812 Because tEXt and zTXt chunks don't have a language field, if you
2813 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2814 any language code or translated keyword will not be written out.
2816 Until text gets around 1000 bytes, it is not worth compressing it.
2817 After the text has been written out to the file, the compression type
2818 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2819 so that it isn't written out again at the end (in case you are calling
2820 png_write_end() with the same struct.
2822 The keywords that are given in the PNG Specification are:
2824 Title Short (one line) title or
2826 Author Name of image's creator
2827 Description Description of image (possibly long)
2828 Copyright Copyright notice
2829 Creation Time Time of original image creation
2830 (usually RFC 1123 format, see below)
2831 Software Software used to create the image
2832 Disclaimer Legal disclaimer
2833 Warning Warning of nature of content
2834 Source Device used to create the image
2835 Comment Miscellaneous comment; conversion
2836 from other image format
2838 The keyword-text pairs work like this. Keywords should be short
2839 simple descriptions of what the comment is about. Some typical
2840 keywords are found in the PNG specification, as is some recommendations
2841 on keywords. You can repeat keywords in a file. You can even write
2842 some text before the image and some after. For example, you may want
2843 to put a description of the image before the image, but leave the
2844 disclaimer until after, so viewers working over modem connections
2845 don't have to wait for the disclaimer to go over the modem before
2846 they start seeing the image. Finally, keywords should be full
2847 words, not abbreviations. Keywords and text are in the ISO 8859-1
2848 (Latin-1) character set (a superset of regular ASCII) and can not
2849 contain NUL characters, and should not contain control or other
2850 unprintable characters. To make the comments widely readable, stick
2851 with basic ASCII, and avoid machine specific character set extensions
2852 like the IBM-PC character set. The keyword must be present, but
2853 you can leave off the text string on non-compressed pairs.
2854 Compressed pairs must have a text string, as only the text string
2855 is compressed anyway, so the compression would be meaningless.
2857 PNG supports modification time via the png_time structure. Two
2858 conversion routines are provided, png_convert_from_time_t() for
2859 time_t and png_convert_from_struct_tm() for struct tm. The
2860 time_t routine uses gmtime(). You don't have to use either of
2861 these, but if you wish to fill in the png_time structure directly,
2862 you should provide the time in universal time (GMT) if possible
2863 instead of your local time. Note that the year number is the full
2864 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2865 that months start with 1.
2867 If you want to store the time of the original image creation, you should
2868 use a plain tEXt chunk with the "Creation Time" keyword. This is
2869 necessary because the "creation time" of a PNG image is somewhat vague,
2870 depending on whether you mean the PNG file, the time the image was
2871 created in a non-PNG format, a still photo from which the image was
2872 scanned, or possibly the subject matter itself. In order to facilitate
2873 machine-readable dates, it is recommended that the "Creation Time"
2874 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2875 although this isn't a requirement. Unlike the tIME chunk, the
2876 "Creation Time" tEXt chunk is not expected to be automatically changed
2877 by the software. To facilitate the use of RFC 1123 dates, a function
2878 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2879 time to an RFC 1123 format string.
2881 .SS Writing unknown chunks
2883 You can use the png_set_unknown_chunks function to queue up chunks
2884 for writing. You give it a chunk name, raw data, and a size; that's
2885 all there is to it. The chunks will be written by the next following
2886 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2887 Any chunks previously read into the info structure's unknown-chunk
2888 list will also be written out in a sequence that satisfies the PNG
2889 specification's ordering rules.
2891 .SS The high-level write interface
2893 At this point there are two ways to proceed; through the high-level
2894 write interface, or through a sequence of low-level write operations.
2895 You can use the high-level interface if your image data is present
2896 in the info structure. All defined output
2897 transformations are permitted, enabled by the following masks.
2899 PNG_TRANSFORM_IDENTITY No transformation
2900 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2901 PNG_TRANSFORM_PACKSWAP Change order of packed
2903 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2904 PNG_TRANSFORM_SHIFT Normalize pixels to the
2906 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2908 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2910 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2912 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2913 PNG_TRANSFORM_STRIP_FILLER Strip out filler
2915 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
2917 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
2920 If you have valid image data in the info structure (you can use
2921 png_set_rows() to put image data in the info structure), simply do this:
2923 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2925 where png_transforms is an integer containing the bitwise OR of some set of
2926 transformation flags. This call is equivalent to png_write_info(),
2927 followed the set of transformations indicated by the transform mask,
2928 then png_write_image(), and finally png_write_end().
2930 (The final parameter of this call is not yet used. Someday it might point
2931 to transformation parameters required by some future output transform.)
2933 You must use png_transforms and not call any png_set_transform() functions
2934 when you use png_write_png().
2936 .SS The low-level write interface
2938 If you are going the low-level route instead, you are now ready to
2939 write all the file information up to the actual image data. You do
2940 this with a call to png_write_info().
2942 png_write_info(png_ptr, info_ptr);
2944 Note that there is one transformation you may need to do before
2945 png_write_info(). In PNG files, the alpha channel in an image is the
2946 level of opacity. If your data is supplied as a level of transparency,
2947 you can invert the alpha channel before you write it, so that 0 is
2948 fully transparent and 255 (in 8-bit or paletted images) or 65535
2949 (in 16-bit images) is fully opaque, with
2951 png_set_invert_alpha(png_ptr);
2953 This must appear before png_write_info() instead of later with the
2954 other transformations because in the case of paletted images the tRNS
2955 chunk data has to be inverted before the tRNS chunk is written. If
2956 your image is not a paletted image, the tRNS data (which in such cases
2957 represents a single color to be rendered as transparent) won't need to
2958 be changed, and you can safely do this transformation after your
2959 png_write_info() call.
2961 If you need to write a private chunk that you want to appear before
2962 the PLTE chunk when PLTE is present, you can write the PNG info in
2963 two steps, and insert code to write your own chunk between them:
2965 png_write_info_before_PLTE(png_ptr, info_ptr);
2966 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2967 png_write_info(png_ptr, info_ptr);
2969 After you've written the file information, you can set up the library
2970 to handle any special transformations of the image data. The various
2971 ways to transform the data will be described in the order that they
2972 should occur. This is important, as some of these change the color
2973 type and/or bit depth of the data, and some others only work on
2974 certain color types and bit depths. Even though each transformation
2975 checks to see if it has data that it can do something with, you should
2976 make sure to only enable a transformation if it will be valid for the
2977 data. For example, don't swap red and blue on grayscale data.
2979 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2980 the library to strip input data that has 4 or 8 bytes per pixel down
2981 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2984 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2986 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2987 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2988 is stored XRGB or RGBX.
2990 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2991 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2992 If the data is supplied at 1 pixel per byte, use this code, which will
2993 correctly pack the pixels into a single byte:
2995 png_set_packing(png_ptr);
2997 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2998 data is of another bit depth, you can write an sBIT chunk into the
2999 file so that decoders can recover the original data if desired.
3001 /* Set the true bit depth of the image data */
3002 if (color_type & PNG_COLOR_MASK_COLOR)
3004 sig_bit.red = true_bit_depth;
3005 sig_bit.green = true_bit_depth;
3006 sig_bit.blue = true_bit_depth;
3010 sig_bit.gray = true_bit_depth;
3012 if (color_type & PNG_COLOR_MASK_ALPHA)
3014 sig_bit.alpha = true_bit_depth;
3017 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3019 If the data is stored in the row buffer in a bit depth other than
3020 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3021 this will scale the values to appear to be the correct bit depth as
3024 png_set_shift(png_ptr, &sig_bit);
3026 PNG files store 16 bit pixels in network byte order (big-endian,
3027 ie. most significant bits first). This code would be used if they are
3028 supplied the other way (little-endian, i.e. least significant bits
3029 first, the way PCs store them):
3032 png_set_swap(png_ptr);
3034 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3035 need to change the order the pixels are packed into bytes, you can use:
3038 png_set_packswap(png_ptr);
3040 PNG files store 3 color pixels in red, green, blue order. This code
3041 would be used if they are supplied as blue, green, red:
3043 png_set_bgr(png_ptr);
3045 PNG files describe monochrome as black being zero and white being
3046 one. This code would be used if the pixels are supplied with this reversed
3047 (black being one and white being zero):
3049 png_set_invert_mono(png_ptr);
3051 Finally, you can write your own transformation function if none of
3052 the existing ones meets your needs. This is done by setting a callback
3055 png_set_write_user_transform_fn(png_ptr,
3056 write_transform_fn);
3058 You must supply the function
3060 void write_transform_fn(png_ptr ptr, row_info_ptr
3061 row_info, png_bytep data)
3063 See pngtest.c for a working example. Your function will be called
3064 before any of the other transformations are processed.
3066 You can also set up a pointer to a user structure for use by your
3069 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3071 The user_channels and user_depth parameters of this function are ignored
3072 when writing; you can set them to zero as shown.
3074 You can retrieve the pointer via the function png_get_user_transform_ptr().
3077 voidp write_user_transform_ptr =
3078 png_get_user_transform_ptr(png_ptr);
3080 It is possible to have libpng flush any pending output, either manually,
3081 or automatically after a certain number of lines have been written. To
3082 flush the output stream a single time call:
3084 png_write_flush(png_ptr);
3086 and to have libpng flush the output stream periodically after a certain
3087 number of scanlines have been written, call:
3089 png_set_flush(png_ptr, nrows);
3091 Note that the distance between rows is from the last time png_write_flush()
3092 was called, or the first row of the image if it has never been called.
3093 So if you write 50 lines, and then png_set_flush 25, it will flush the
3094 output on the next scanline, and every 25 lines thereafter, unless
3095 png_write_flush() is called before 25 more lines have been written.
3096 If nrows is too small (less than about 10 lines for a 640 pixel wide
3097 RGB image) the image compression may decrease noticeably (although this
3098 may be acceptable for real-time applications). Infrequent flushing will
3099 only degrade the compression performance by a few percent over images
3100 that do not use flushing.
3102 .SS Writing the image data
3104 That's it for the transformations. Now you can write the image data.
3105 The simplest way to do this is in one function call. If you have the
3106 whole image in memory, you can just call png_write_image() and libpng
3107 will write the image. You will need to pass in an array of pointers to
3108 each row. This function automatically handles interlacing, so you don't
3109 need to call png_set_interlace_handling() or call this function multiple
3110 times, or any of that other stuff necessary with png_write_rows().
3112 png_write_image(png_ptr, row_pointers);
3114 where row_pointers is:
3116 png_byte *row_pointers[height];
3118 You can point to void or char or whatever you use for pixels.
3120 If you don't want to write the whole image at once, you can
3121 use png_write_rows() instead. If the file is not interlaced,
3124 png_write_rows(png_ptr, row_pointers,
3127 row_pointers is the same as in the png_write_image() call.
3129 If you are just writing one row at a time, you can do this with
3130 a single row_pointer instead of an array of row_pointers:
3132 png_bytep row_pointer = row;
3134 png_write_row(png_ptr, row_pointer);
3136 When the file is interlaced, things can get a good deal more complicated.
3137 The only currently (as of the PNG Specification version 1.2, dated July
3138 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
3139 scheme, that breaks down an image into seven smaller images of varying
3140 size. libpng will build these images for you, or you can do them
3141 yourself. If you want to build them yourself, see the PNG specification
3142 for details of which pixels to write when.
3144 If you don't want libpng to handle the interlacing details, just
3145 use png_set_interlace_handling() and call png_write_rows() the
3146 correct number of times to write all seven sub-images.
3148 If you want libpng to build the sub-images, call this before you start
3152 png_set_interlace_handling(png_ptr);
3154 This will return the number of passes needed. Currently, this is seven,
3155 but may change if another interlace type is added.
3157 Then write the complete image number_of_passes times.
3159 png_write_rows(png_ptr, row_pointers,
3162 As some of these rows are not used, and thus return immediately, you may
3163 want to read about interlacing in the PNG specification, and only update
3164 the rows that are actually used.
3166 .SS Finishing a sequential write
3168 After you are finished writing the image, you should finish writing
3169 the file. If you are interested in writing comments or time, you should
3170 pass an appropriately filled png_info pointer. If you are not interested,
3173 png_write_end(png_ptr, info_ptr);
3175 When you are done, you can free all memory used by libpng like this:
3177 png_destroy_write_struct(&png_ptr, &info_ptr);
3179 It is also possible to individually free the info_ptr members that
3180 point to libpng-allocated storage with the following function:
3182 png_free_data(png_ptr, info_ptr, mask, seq)
3183 mask - identifies data to be freed, a mask
3184 containing the bitwise OR of one or
3186 PNG_FREE_PLTE, PNG_FREE_TRNS,
3187 PNG_FREE_HIST, PNG_FREE_ICCP,
3188 PNG_FREE_PCAL, PNG_FREE_ROWS,
3189 PNG_FREE_SCAL, PNG_FREE_SPLT,
3190 PNG_FREE_TEXT, PNG_FREE_UNKN,
3191 or simply PNG_FREE_ALL
3192 seq - sequence number of item to be freed
3195 This function may be safely called when the relevant storage has
3196 already been freed, or has not yet been allocated, or was allocated
3197 by the user and not by libpng, and will in those cases do nothing.
3198 The "seq" parameter is ignored if only one item of the selected data
3199 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3200 are allowed for the data type identified in the mask, such as text or
3201 sPLT, only the n'th item in the structure is freed, where n is "seq".
3203 If you allocated data such as a palette that you passed in to libpng
3204 with png_set_*, you must not free it until just before the call to
3205 png_destroy_write_struct().
3207 The default behavior is only to free data that was allocated internally
3208 by libpng. This can be changed, so that libpng will not free the data,
3209 or so that it will free data that was allocated by the user with png_malloc()
3210 or png_zalloc() and passed in via a png_set_*() function, with
3212 png_data_freer(png_ptr, info_ptr, freer, mask)
3213 mask - which data elements are affected
3214 same choices as in png_free_data()
3216 PNG_DESTROY_WILL_FREE_DATA
3217 PNG_SET_WILL_FREE_DATA
3218 PNG_USER_WILL_FREE_DATA
3220 For example, to transfer responsibility for some data from a read structure
3221 to a write structure, you could use
3223 png_data_freer(read_ptr, read_info_ptr,
3224 PNG_USER_WILL_FREE_DATA,
3225 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3226 png_data_freer(write_ptr, write_info_ptr,
3227 PNG_DESTROY_WILL_FREE_DATA,
3228 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3230 thereby briefly reassigning responsibility for freeing to the user but
3231 immediately afterwards reassigning it once more to the write_destroy
3232 function. Having done this, it would then be safe to destroy the read
3233 structure and continue to use the PLTE, tRNS, and hIST data in the write
3236 This function only affects data that has already been allocated.
3237 You can call this function before calling after the png_set_*() functions
3238 to control whether the user or png_destroy_*() is supposed to free the data.
3239 When the user assumes responsibility for libpng-allocated data, the
3240 application must use
3241 png_free() to free it, and when the user transfers responsibility to libpng
3242 for data that the user has allocated, the user must have used png_malloc()
3243 or png_zalloc() to allocate it.
3245 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3246 separately, do not transfer responsibility for freeing text_ptr to libpng,
3247 because when libpng fills a png_text structure it combines these members with
3248 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3249 if you transfer responsibility for free'ing text_ptr from libpng to your
3250 application, your application must not separately free those members.
3251 For a more compact example of writing a PNG image, see the file example.c.
3253 .SH V. Modifying/Customizing libpng:
3255 There are two issues here. The first is changing how libpng does
3256 standard things like memory allocation, input/output, and error handling.
3257 The second deals with more complicated things like adding new chunks,
3258 adding new transformations, and generally changing how libpng works.
3259 Both of those are compile-time issues; that is, they are generally
3260 determined at the time the code is written, and there is rarely a need
3261 to provide the user with a means of changing them.
3263 Memory allocation, input/output, and error handling
3265 All of the memory allocation, input/output, and error handling in libpng
3266 goes through callbacks that are user-settable. The default routines are
3267 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3268 these functions, call the appropriate png_set_*_fn() function.
3270 Memory allocation is done through the functions png_malloc(), png_calloc(),
3271 and png_free(). These currently just call the standard C functions.
3272 png_calloc() calls png_malloc() and then png_memset() to clear the newly
3273 allocated memory to zero. If your pointers can't access more then 64K
3274 at a time, you will want to set MAXSEG_64K in zlib.h. Since it is
3275 unlikely that the method of handling memory allocation on a platform
3276 will change between applications, these functions must be modified in
3277 the library at compile time. If you prefer to use a different method
3278 of allocating and freeing data, you can use png_create_read_struct_2() or
3279 png_create_write_struct_2() to register your own functions as described
3280 above. These functions also provide a void pointer that can be retrieved
3283 mem_ptr=png_get_mem_ptr(png_ptr);
3285 Your replacement memory functions must have prototypes as follows:
3287 png_voidp malloc_fn(png_structp png_ptr,
3288 png_alloc_size_t size);
3289 void free_fn(png_structp png_ptr, png_voidp ptr);
3291 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3292 function will normally call png_error() if it receives a NULL from the
3293 system memory allocator or from your replacement malloc_fn().
3295 Your free_fn() will never be called with a NULL ptr, since libpng's
3296 png_free() checks for NULL before calling free_fn().
3298 Input/Output in libpng is done through png_read() and png_write(),
3299 which currently just call fread() and fwrite(). The FILE * is stored in
3300 png_struct and is initialized via png_init_io(). If you wish to change
3301 the method of I/O, the library supplies callbacks that you can set
3302 through the function png_set_read_fn() and png_set_write_fn() at run
3303 time, instead of calling the png_init_io() function. These functions
3304 also provide a void pointer that can be retrieved via the function
3305 png_get_io_ptr(). For example:
3307 png_set_read_fn(png_structp read_ptr,
3308 voidp read_io_ptr, png_rw_ptr read_data_fn)
3310 png_set_write_fn(png_structp write_ptr,
3311 voidp write_io_ptr, png_rw_ptr write_data_fn,
3312 png_flush_ptr output_flush_fn);
3314 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3315 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3317 The replacement I/O functions must have prototypes as follows:
3319 void user_read_data(png_structp png_ptr,
3320 png_bytep data, png_size_t length);
3321 void user_write_data(png_structp png_ptr,
3322 png_bytep data, png_size_t length);
3323 void user_flush_data(png_structp png_ptr);
3325 The user_read_data() function is responsible for detecting and
3326 handling end-of-data errors.
3328 Supplying NULL for the read, write, or flush functions sets them back
3329 to using the default C stream functions, which expect the io_ptr to
3330 point to a standard *FILE structure. It is probably a mistake
3331 to use NULL for one of write_data_fn and output_flush_fn but not both
3332 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
3333 It is an error to read from a write stream, and vice versa.
3335 Error handling in libpng is done through png_error() and png_warning().
3336 Errors handled through png_error() are fatal, meaning that png_error()
3337 should never return to its caller. Currently, this is handled via
3338 setjmp() and longjmp() (unless you have compiled libpng with
3339 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3340 but you could change this to do things like exit() if you should wish.
3342 On non-fatal errors, png_warning() is called
3343 to print a warning message, and then control returns to the calling code.
3344 By default png_error() and png_warning() print a message on stderr via
3345 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3346 (because you don't want the messages) or PNG_NO_STDIO defined (because
3347 fprintf() isn't available). If you wish to change the behavior of the error
3348 functions, you will need to set up your own message callbacks. These
3349 functions are normally supplied at the time that the png_struct is created.
3350 It is also possible to redirect errors and warnings to your own replacement
3351 functions after png_create_*_struct() has been called by calling:
3353 png_set_error_fn(png_structp png_ptr,
3354 png_voidp error_ptr, png_error_ptr error_fn,
3355 png_error_ptr warning_fn);
3357 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3359 If NULL is supplied for either error_fn or warning_fn, then the libpng
3360 default function will be used, calling fprintf() and/or longjmp() if a
3361 problem is encountered. The replacement error functions should have
3362 parameters as follows:
3364 void user_error_fn(png_structp png_ptr,
3365 png_const_charp error_msg);
3366 void user_warning_fn(png_structp png_ptr,
3367 png_const_charp warning_msg);
3369 The motivation behind using setjmp() and longjmp() is the C++ throw and
3370 catch exception handling methods. This makes the code much easier to write,
3371 as there is no need to check every return code of every function call.
3372 However, there are some uncertainties about the status of local variables
3373 after a longjmp, so the user may want to be careful about doing anything
3374 after setjmp returns non-zero besides returning itself. Consult your
3375 compiler documentation for more details. For an alternative approach, you
3376 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3380 If you need to read or write custom chunks, you may need to get deeper
3381 into the libpng code. The library now has mechanisms for storing
3382 and writing chunks of unknown type; you can even declare callbacks
3383 for custom chunks. However, this may not be good enough if the
3384 library code itself needs to know about interactions between your
3385 chunk and existing `intrinsic' chunks.
3387 If you need to write a new intrinsic chunk, first read the PNG
3388 specification. Acquire a first level of understanding of how it works.
3389 Pay particular attention to the sections that describe chunk names,
3390 and look at how other chunks were designed, so you can do things
3391 similarly. Second, check out the sections of libpng that read and
3392 write chunks. Try to find a chunk that is similar to yours and use
3393 it as a template. More details can be found in the comments inside
3394 the code. It is best to handle unknown chunks in a generic method,
3395 via callback functions, instead of by modifying libpng functions.
3397 If you wish to write your own transformation for the data, look through
3398 the part of the code that does the transformations, and check out some of
3399 the simpler ones to get an idea of how they work. Try to find a similar
3400 transformation to the one you want to add and copy off of it. More details
3401 can be found in the comments inside the code itself.
3403 .SS Configuring for 16 bit platforms
3405 You will want to look into zconf.h to tell zlib (and thus libpng) that
3406 it cannot allocate more then 64K at a time. Even if you can, the memory
3407 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3409 .SS Configuring for DOS
3411 For DOS users who only have access to the lower 640K, you will
3412 have to limit zlib's memory usage via a png_set_compression_mem_level()
3413 call. See zlib.h or zconf.h in the zlib library for more information.
3415 .SS Configuring for Medium Model
3417 Libpng's support for medium model has been tested on most of the popular
3418 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3419 defined, and FAR gets defined to far in pngconf.h, and you should be
3420 all set. Everything in the library (except for zlib's structure) is
3421 expecting far data. You must use the typedefs with the p or pp on
3422 the end for pointers (or at least look at them and be careful). Make
3423 note that the rows of data are defined as png_bytepp, which is an
3424 unsigned char far * far *.
3426 .SS Configuring for gui/windowing platforms:
3428 You will need to write new error and warning functions that use the GUI
3429 interface, as described previously, and set them to be the error and
3430 warning functions at the time that png_create_*_struct() is called,
3431 in order to have them available during the structure initialization.
3432 They can be changed later via png_set_error_fn(). On some compilers,
3433 you may also have to change the memory allocators (png_malloc, etc.).
3435 .SS Configuring for compiler xxx:
3437 All includes for libpng are in pngconf.h. If you need to add, change
3438 or delete an include, this is the place to do it.
3439 The includes that are not needed outside libpng are placed in pngpriv.h,
3440 which is only used by the routines inside libpng itself.
3441 The files in libpng proper only include pngpriv.h and png.h, which
3442 in turn includes pngconf.h.
3444 .SS Configuring zlib:
3446 There are special functions to configure the compression. Perhaps the
3447 most useful one changes the compression level, which currently uses
3448 input compression values in the range 0 - 9. The library normally
3449 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3450 have shown that for a large majority of images, compression values in
3451 the range 3-6 compress nearly as well as higher levels, and do so much
3452 faster. For online applications it may be desirable to have maximum speed
3453 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3454 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3455 files larger than just storing the raw bitmap. You can specify the
3456 compression level by calling:
3458 png_set_compression_level(png_ptr, level);
3460 Another useful one is to reduce the memory level used by the library.
3461 The memory level defaults to 8, but it can be lowered if you are
3462 short on memory (running DOS, for example, where you only have 640K).
3463 Note that the memory level does have an effect on compression; among
3464 other things, lower levels will result in sections of incompressible
3465 data being emitted in smaller stored blocks, with a correspondingly
3466 larger relative overhead of up to 15% in the worst case.
3468 png_set_compression_mem_level(png_ptr, level);
3470 The other functions are for configuring zlib. They are not recommended
3471 for normal use and may result in writing an invalid PNG file. See
3472 zlib.h for more information on what these mean.
3474 png_set_compression_strategy(png_ptr,
3476 png_set_compression_window_bits(png_ptr,
3478 png_set_compression_method(png_ptr, method);
3479 png_set_compression_buffer_size(png_ptr, size);
3481 .SS Controlling row filtering
3483 If you want to control whether libpng uses filtering or not, which
3484 filters are used, and how it goes about picking row filters, you
3485 can call one of these functions. The selection and configuration
3486 of row filters can have a significant impact on the size and
3487 encoding speed and a somewhat lesser impact on the decoding speed
3488 of an image. Filtering is enabled by default for RGB and grayscale
3489 images (with and without alpha), but not for paletted images nor
3490 for any images with bit depths less than 8 bits/pixel.
3492 The 'method' parameter sets the main filtering method, which is
3493 currently only '0' in the PNG 1.2 specification. The 'filters'
3494 parameter sets which filter(s), if any, should be used for each
3495 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3496 to turn filtering on and off, respectively.
3498 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3499 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3500 ORed together with '|' to specify one or more filters to use.
3501 These filters are described in more detail in the PNG specification.
3502 If you intend to change the filter type during the course of writing
3503 the image, you should start with flags set for all of the filters
3504 you intend to use so that libpng can initialize its internal
3505 structures appropriately for all of the filter types. (Note that this
3506 means the first row must always be adaptively filtered, because libpng
3507 currently does not allocate the filter buffers until png_write_row()
3508 is called for the first time.)
3510 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3511 PNG_FILTER_UP | PNG_FILTER_AVG |
3512 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3514 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3516 The second parameter can also be
3517 PNG_INTRAPIXEL_DIFFERENCING if you are
3518 writing a PNG to be embedded in a MNG
3519 datastream. This parameter must be the
3520 same as the value of filter_method used
3523 It is also possible to influence how libpng chooses from among the
3524 available filters. This is done in one or both of two ways - by
3525 telling it how important it is to keep the same filter for successive
3526 rows, and by telling it the relative computational costs of the filters.
3528 double weights[3] = {1.5, 1.3, 1.1},
3529 costs[PNG_FILTER_VALUE_LAST] =
3530 {1.0, 1.3, 1.3, 1.5, 1.7};
3532 png_set_filter_heuristics(png_ptr,
3533 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3536 The weights are multiplying factors that indicate to libpng that the
3537 row filter should be the same for successive rows unless another row filter
3538 is that many times better than the previous filter. In the above example,
3539 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3540 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3541 and still be chosen, while the NONE filter could have a sum 1.1 times
3542 higher than other filters and still be chosen. Unspecified weights are
3543 taken to be 1.0, and the specified weights should probably be declining
3544 like those above in order to emphasize recent filters over older filters.
3546 The filter costs specify for each filter type a relative decoding cost
3547 to be considered when selecting row filters. This means that filters
3548 with higher costs are less likely to be chosen over filters with lower
3549 costs, unless their "sum of absolute differences" is that much smaller.
3550 The costs do not necessarily reflect the exact computational speeds of
3551 the various filters, since this would unduly influence the final image
3554 Note that the numbers above were invented purely for this example and
3555 are given only to help explain the function usage. Little testing has
3556 been done to find optimum values for either the costs or the weights.
3558 .SS Removing unwanted object code
3560 There are a bunch of #define's in pngconf.h that control what parts of
3561 libpng are compiled. All the defines end in _SUPPORTED. If you are
3562 never going to use a capability, you can change the #define to #undef
3563 before recompiling libpng and save yourself code and data space, or
3564 you can turn off individual capabilities with defines that begin with
3567 You can also turn all of the transforms and ancillary chunk capabilities
3568 off en masse with compiler directives that define
3569 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3571 along with directives to turn on any of the capabilities that you do
3572 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
3573 transformations but still leave the library fully capable of reading
3574 and writing PNG files with all known public chunks. Use of the
3575 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
3576 that is incapable of reading or writing ancillary chunks. If you are
3577 not using the progressive reading capability, you can turn that off
3578 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
3579 capability, which you'll still have).
3581 All the reading and writing specific code are in separate files, so the
3582 linker should only grab the files it needs. However, if you want to
3583 make sure, or if you are building a stand alone library, all the
3584 reading files start with pngr and all the writing files start with
3585 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3586 are used for both reading and writing, and always need to be included.
3587 The progressive reader is in pngpread.c
3589 If you are creating or distributing a dynamically linked library (a .so
3590 or DLL file), you should not remove or disable any parts of the library,
3591 as this will cause applications linked with different versions of the
3592 library to fail if they call functions not available in your library.
3593 The size of the library itself should not be an issue, because only
3594 those sections that are actually used will be loaded into memory.
3596 .SS Requesting debug printout
3598 The macro definition PNG_DEBUG can be used to request debugging
3599 printout. Set it to an integer value in the range 0 to 3. Higher
3600 numbers result in increasing amounts of debugging information. The
3601 information is printed to the "stderr" file, unless another file
3602 name is specified in the PNG_DEBUG_FILE macro definition.
3604 When PNG_DEBUG > 0, the following functions (macros) become available:
3606 png_debug(level, message)
3607 png_debug1(level, message, p1)
3608 png_debug2(level, message, p1, p2)
3610 in which "level" is compared to PNG_DEBUG to decide whether to print
3611 the message, "message" is the formatted string to be printed,
3612 and p1 and p2 are parameters that are to be embedded in the string
3613 according to printf-style formatting directives. For example,
3615 png_debug1(2, "foo=%d\n", foo);
3620 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3622 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3623 can still use PNG_DEBUG to control your own debugging:
3629 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3630 having level = 0 will be printed. There aren't any such statements in
3631 this version of libpng, but if you insert some they will be printed.
3635 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3636 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3637 Libpng can support some of these extensions. To enable them, use the
3638 png_permit_mng_features() function:
3640 feature_set = png_permit_mng_features(png_ptr, mask)
3641 mask is a png_uint_32 containing the bitwise OR of the
3642 features you want to enable. These include
3643 PNG_FLAG_MNG_EMPTY_PLTE
3644 PNG_FLAG_MNG_FILTER_64
3645 PNG_ALL_MNG_FEATURES
3646 feature_set is a png_uint_32 that is the bitwise AND of
3647 your mask with the set of MNG features that is
3648 supported by the version of libpng that you are using.
3650 It is an error to use this function when reading or writing a standalone
3651 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3652 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3653 and the MHDR and MEND chunks. Libpng does not provide support for these
3654 or any other MNG chunks; your application must provide its own support for
3655 them. You may wish to consider using libmng (available at
3656 http://www.libmng.com) instead.
3658 .SH VII. Changes to Libpng from version 0.88
3660 It should be noted that versions of libpng later than 0.96 are not
3661 distributed by the original libpng author, Guy Schalnat, nor by
3662 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3663 distributed versions 0.89 through 0.96, but rather by another member
3664 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3665 still alive and well, but they have moved on to other things.
3667 The old libpng functions png_read_init(), png_write_init(),
3668 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3669 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3670 functions will be removed from libpng version 2.0.0.
3672 The preferred method of creating and initializing the libpng structures is
3673 via the png_create_read_struct(), png_create_write_struct(), and
3674 png_create_info_struct() because they isolate the size of the structures
3675 from the application, allow version error checking, and also allow the
3676 use of custom error handling routines during the initialization, which
3677 the old functions do not. The functions png_read_destroy() and
3678 png_write_destroy() do not actually free the memory that libpng
3679 allocated for these structs, but just reset the data structures, so they
3680 can be used instead of png_destroy_read_struct() and
3681 png_destroy_write_struct() if you feel there is too much system overhead
3682 allocating and freeing the png_struct for each image read.
3684 Setting the error callbacks via png_set_message_fn() before
3685 png_read_init() as was suggested in libpng-0.88 is no longer supported
3686 because this caused applications that do not use custom error functions
3687 to fail if the png_ptr was not initialized to zero. It is still possible
3688 to set the error callbacks AFTER png_read_init(), or to change them with
3689 png_set_error_fn(), which is essentially the same function, but with a new
3690 name to force compilation errors with applications that try to use the old
3693 Starting with version 1.0.7, you can find out which version of the library
3694 you are using at run-time:
3696 png_uint_32 libpng_vn = png_access_version_number();
3698 The number libpng_vn is constructed from the major version, minor
3699 version with leading zero, and release number with leading zero,
3700 (e.g., libpng_vn for version 1.0.7 is 10007).
3702 You can also check which version of png.h you used when compiling your
3705 png_uint_32 application_vn = PNG_LIBPNG_VER;
3707 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
3709 Support for user memory management was enabled by default. To
3710 accomplish this, the functions png_create_read_struct_2(),
3711 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
3712 png_malloc_default(), and png_free_default() were added.
3714 Support for the iTXt chunk has been enabled by default as of
3717 Support for certain MNG features was enabled.
3719 Support for numbered error messages was added. However, we never got
3720 around to actually numbering the error messages. The function
3721 png_set_strip_error_numbers() was added (Note: the prototype for this
3722 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
3723 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
3725 The png_malloc_warn() function was added at libpng-1.2.3. This issues
3726 a png_warning and returns NULL instead of aborting when it fails to
3727 acquire the requested memory allocation.
3729 Support for setting user limits on image width and height was enabled
3730 by default. The functions png_set_user_limits(), png_get_user_width_max(),
3731 and png_get_user_height_max() were added at libpng-1.2.6.
3733 The png_set_add_alpha() function was added at libpng-1.2.7.
3735 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
3736 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
3737 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
3740 A number of macro definitions in support of runtime selection of
3741 assembler code features (especially Intel MMX code support) were
3742 added at libpng-1.2.0:
3744 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
3745 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
3746 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
3747 PNG_ASM_FLAG_MMX_READ_INTERLACE
3748 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
3749 PNG_ASM_FLAG_MMX_READ_FILTER_UP
3750 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
3751 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
3752 PNG_ASM_FLAGS_INITIALIZED
3758 We added the following functions in support of runtime
3759 selection of assembler code features:
3761 png_get_mmx_flagmask()
3762 png_set_mmx_thresholds()
3764 png_get_mmx_bitdepth_threshold()
3765 png_get_mmx_rowbytes_threshold()
3768 We replaced all of these functions with simple stubs in libpng-1.2.20,
3769 when the Intel assembler code was removed due to a licensing issue.
3771 These macros are deprecated:
3773 PNG_READ_TRANSFORMS_NOT_SUPPORTED
3774 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
3775 PNG_NO_SEQUENTIAL_READ_SUPPORTED
3776 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
3777 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
3778 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
3780 They have been replaced, respectively, by:
3782 PNG_NO_READ_TRANSFORMS
3783 PNG_NO_PROGRESSIVE_READ
3784 PNG_NO_SEQUENTIAL_READ
3785 PNG_NO_WRITE_TRANSFORMS
3786 PNG_NO_READ_ANCILLARY_CHUNKS
3787 PNG_NO_WRITE_ANCILLARY_CHUNKS
3789 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
3790 deprecated since libpng-1.0.16 and libpng-1.2.6.
3793 png_check_sig(sig, num)
3795 !png_sig_cmp(sig, 0, num)
3796 It has been deprecated since libpng-0.90.
3799 png_set_gray_1_2_4_to_8()
3800 which also expands tRNS to alpha was replaced with
3801 png_set_expand_gray_1_2_4_to_8()
3802 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
3804 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
3806 Private libpng prototypes and macro definitions were moved from
3807 png.h and pngconf.h into a new pngpriv.h header file.
3809 Functions png_set_benign_errors(), png_benign_error(), and
3810 png_chunk_benign_error() were added.
3812 Support for setting the maximum amount of memory that the application
3813 will allocate for reading chunks was added, as a security measure.
3814 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
3815 were added to the library.
3817 We implemented support for I/O states by adding png_ptr member io_state
3818 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
3820 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
3823 Checking for and reporting of errors in the IHDR chunk is more thorough.
3825 Support for global arrays was removed, to improve thread safety.
3827 Some obsolete/deprecated macros and functions have been removed.
3829 Typecasted NULL definitions such as
3830 #define png_voidp_NULL (png_voidp)NULL
3831 were eliminated. If you used these in your application, just use
3834 The png_struct and info_struct members "trans" and "trans_values" were
3835 changed to "trans_alpha" and "trans_color", respectively.
3837 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
3840 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
3842 The PNG_LEGACY_SUPPORTED macro was eliminated.
3844 Many WIN32_WCE #ifdefs were removed.
3846 The functions png_read_init(info_ptr), png_write_init(info_ptr),
3847 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
3848 have been removed. They have been deprecated since libpng-0.95.
3850 The png_permit_empty_plte() was removed. It has been deprecated
3851 since libpng-1.0.9. Use png_permit_mng_features() instead.
3853 We removed the obsolete stub functions png_get_mmx_flagmask(),
3854 png_set_mmx_thresholds(), png_get_asm_flags(),
3855 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
3856 png_set_asm_flags(), and png_mmx_supported()
3858 We removed the obsolete png_check_sig(), png_memcpy_check(), and
3859 png_memset_check() functions. Instead use !png_sig_cmp(), png_memcpy(),
3860 and png_memset(), respectively.
3862 The function png_set_gray_1_2_4_to_8() was removed. It has been
3863 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
3864 png_set_expand_gray_1_2_4_to_8() because the former function also
3865 expanded palette images.
3867 We changed the prototype for png_malloc() from
3868 png_malloc(png_structp png_ptr, png_uint_32 size)
3870 png_malloc(png_structp png_ptr, png_alloc_size_t size)
3872 This also applies to the prototype for the user replacement malloc_fn().
3874 The png_calloc() function was added and is used in place of
3875 of "png_malloc(); png_memset();" except in the case in png_read_png()
3876 where the array consists of pointers; in this case a "for" loop is used
3877 after the png_malloc() to set the pointers to NULL, to give robust.
3878 behavior in case the application runs out of memory part-way through
3881 We changed the prototypes of png_get_compression_buffer_size() and
3882 png_set_compression_buffer_size() to work with png_size_t instead of
3885 Support for numbered error messages was removed by default, since we
3886 never got around to actually numbering the error messages. The function
3887 png_set_strip_error_numbers() was removed from the library by default.
3889 The png_zalloc() and png_zfree() functions are no longer exported.
3890 The png_zalloc() function no longer zeroes out the memory that it
3893 We removed the trailing '.' from the warning and error messages.
3895 .SH X. Detecting libpng
3897 The png_get_io_ptr() function has been present since libpng-0.88, has never
3898 changed, and is unaffected by conditional compilation macros. It is the
3899 best choice for use in configure scripts for detecting the presence of any
3900 libpng version since 0.88. In an autoconf "configure.in" you could use
3902 AC_CHECK_LIB(png, png_get_io_ptr, ...
3904 .SH XI. Source code repository
3906 Since about February 2009, version 1.2.34, libpng has been under "git" source
3907 control. The git repository was built from old libpng-x.y.z.tar.gz files
3908 going back to version 0.70. You can access the git repository (read only)
3911 git://libpng.git.sourceforge.net/gitroot/libpng
3913 or you can browse it via "gitweb" at
3915 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
3917 Patches can be sent to glennrp at users.sourceforge.net or to
3918 png-mng-implement at lists.sourceforge.net or you can upload them to
3919 the libpng bug tracker at
3921 http://libpng.sourceforge.net
3923 .SH XII. Coding style
3925 Our coding style is similar to the "Allman" style, with curly
3926 braces on separate lines:
3933 else if (another condition)
3938 The braces can be omitted from simple one-line actions:
3943 We use 3-space indentation, except for continued statements which
3944 are usually indented the same as the first line of the statement
3945 plus four more spaces.
3947 For macro definitions we use 2-space indentation, always leaving the "#"
3948 in the first column.
3950 #ifndef PNG_NO_FEATURE
3951 # ifndef PNG_FEATURE_SUPPORTED
3952 # define PNG_FEATURE_SUPPORTED
3956 Comments appear with the leading "/*" at the same indentation as
3957 the statement that follows the comment:
3959 /* Single-line comment */
3967 Very short comments can be placed at the end of the statement
3968 to which they pertain:
3970 statement; /* comment */
3972 We don't use C++ style ("//") comments. We have, however,
3973 used them in the past in some now-abandoned MMX assembler
3976 Functions and their curly braces are not indented, and
3977 exported functions are marked with PNGAPI:
3979 /* This is a public function that is visible to
3980 * application programers. It does thus-and-so.
3983 png_exported_function(png_ptr, png_info, foo)
3988 The prototypes for all exported functions appear in png.h,
3989 above the comment that says
3991 /* Maintainer: Put new public prototypes here ... */
3993 We mark all non-exported functions with "/* PRIVATE */"":
3996 png_non_exported_function(png_ptr, png_info, foo)
4001 The prototypes for non-exported functions (except for those in
4004 above the comment that says
4006 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
4008 The names of all exported functions and variables begin
4009 with "png_", and all publicly visible C preprocessor
4010 macros begin with "PNG_".
4012 We put a space after each comma and after each semicolon
4013 in "for" statments, and we put spaces before and after each
4014 C binary operator and after "for" or "while". We don't
4015 put a space between a typecast and the expression being
4016 cast, nor do we put one between a function name and the
4017 left parenthesis that follows it:
4019 for (i = 2; i > 0; --i)
4020 y[i] = a(x) + (int)b;
4022 We prefer #ifdef and #ifndef to #if defined() and if !defined()
4023 when there is only one macro being tested.
4025 We do not use the TAB character for indentation in the C sources.
4027 Lines do not exceed 80 characters.
4029 Other rules can be inferred by inspecting the libpng source.
4031 .SH XIII. Y2K Compliance in libpng
4035 Since the PNG Development group is an ad-hoc body, we can't make
4036 an official declaration.
4038 This is your unofficial assurance that libpng from version 0.71 and
4039 upward through 1.4.1 are Y2K compliant. It is my belief that earlier
4040 versions were also Y2K compliant.
4042 Libpng only has three year fields. One is a 2-byte unsigned integer that
4043 will hold years up to 65535. The other two hold the date in text
4044 format, and will hold years up to 9999.
4047 "png_uint_16 year" in png_time_struct.
4050 "png_charp time_buffer" in png_struct and
4051 "near_time_buffer", which is a local character string in png.c.
4053 There are seven time-related functions:
4055 png_convert_to_rfc_1123() in png.c
4056 (formerly png_convert_to_rfc_1152() in error)
4057 png_convert_from_struct_tm() in pngwrite.c, called
4059 png_convert_from_time_t() in pngwrite.c
4060 png_get_tIME() in pngget.c
4061 png_handle_tIME() in pngrutil.c, called in pngread.c
4062 png_set_tIME() in pngset.c
4063 png_write_tIME() in pngwutil.c, called in pngwrite.c
4065 All appear to handle dates properly in a Y2K environment. The
4066 png_convert_from_time_t() function calls gmtime() to convert from system
4067 clock time, which returns (year - 1900), which we properly convert to
4068 the full 4-digit year. There is a possibility that applications using
4069 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
4070 function, or that they are incorrectly passing only a 2-digit year
4071 instead of "year - 1900" into the png_convert_from_struct_tm() function,
4072 but this is not under our control. The libpng documentation has always
4073 stated that it works with 4-digit years, and the APIs have been
4076 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
4077 integer to hold the year, and can hold years as large as 65535.
4079 zlib, upon which libpng depends, is also Y2K compliant. It contains
4080 no date-related code.
4083 Glenn Randers-Pehrson
4085 PNG Development Group
4089 Note about libpng version numbers:
4091 Due to various miscommunications, unforeseen code incompatibilities
4092 and occasional factors outside the authors' control, version numbering
4093 on the library has not always been consistent and straightforward.
4094 The following table summarizes matters since version 0.89c, which was
4095 the first widely used release:
4097 source png.h png.h shared-lib
4098 version string int version
4099 ------- ------ ----- ----------
4100 0.89c ("beta 3") 0.89 89 1.0.89
4101 0.90 ("beta 4") 0.90 90 0.90
4102 0.95 ("beta 5") 0.95 95 0.95
4103 0.96 ("beta 6") 0.96 96 0.96
4104 0.97b ("beta 7") 1.00.97 97 1.0.1
4105 0.97c 0.97 97 2.0.97
4108 0.99a-m 0.99 99 2.0.99
4110 1.0.0 1.0.0 100 2.1.0
4111 1.0.0 (from here on, the 100 2.1.0
4112 1.0.1 png.h string is 10001 2.1.0
4113 1.0.1a-e identical to the 10002 from here on, the
4114 1.0.2 source version) 10002 shared library is 2.V
4115 1.0.2a-b 10003 where V is the source
4116 1.0.1 10001 code version except as
4117 1.0.1a-e 10002 2.1.0.1a-e noted.
4119 1.0.2a-b 10003 2.1.0.2a-b
4121 1.0.3a-d 10004 2.1.0.3a-d
4123 1.0.4a-f 10005 2.1.0.4a-f
4124 1.0.5 (+ 2 patches) 10005 2.1.0.5
4125 1.0.5a-d 10006 2.1.0.5a-d
4126 1.0.5e-r 10100 2.1.0.5e-r
4127 1.0.5s-v 10006 2.1.0.5s-v
4128 1.0.6 (+ 3 patches) 10006 2.1.0.6
4129 1.0.6d-g 10007 2.1.0.6d-g
4132 1.0.6j 10007 2.1.0.6j
4133 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
4134 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
4135 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
4136 1.0.7 1 10007 2.1.0.7
4137 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
4138 1.0.8rc1 1 10008 2.1.0.8rc1
4139 1.0.8 1 10008 2.1.0.8
4140 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
4141 1.0.9rc1 1 10009 2.1.0.9rc1
4142 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
4143 1.0.9rc2 1 10009 2.1.0.9rc2
4144 1.0.9 1 10009 2.1.0.9
4145 1.0.10beta1 1 10010 2.1.0.10beta1
4146 1.0.10rc1 1 10010 2.1.0.10rc1
4147 1.0.10 1 10010 2.1.0.10
4148 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
4149 1.0.11rc1 1 10011 2.1.0.11rc1
4150 1.0.11 1 10011 2.1.0.11
4151 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
4152 1.0.12rc1 2 10012 2.1.0.12rc1
4153 1.0.12 2 10012 2.1.0.12
4154 1.1.0a-f - 10100 2.1.1.0a-f abandoned
4155 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
4156 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
4157 1.2.0rc1 3 10200 3.1.2.0rc1
4158 1.2.0 3 10200 3.1.2.0
4159 1.2.1beta-4 3 10201 3.1.2.1beta1-4
4160 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
4161 1.2.1 3 10201 3.1.2.1
4162 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
4163 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
4164 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
4165 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
4166 1.0.13 10 10013 10.so.0.1.0.13
4167 1.2.2 12 10202 12.so.0.1.2.2
4168 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
4169 1.2.3 12 10203 12.so.0.1.2.3
4170 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
4171 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
4172 1.0.14 10 10014 10.so.0.1.0.14
4173 1.2.4 13 10204 12.so.0.1.2.4
4174 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
4175 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
4176 1.0.15 10 10015 10.so.0.1.0.15
4177 1.2.5 13 10205 12.so.0.1.2.5
4178 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
4179 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
4180 1.0.16 10 10016 10.so.0.1.0.16
4181 1.2.6 13 10206 12.so.0.1.2.6
4182 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
4183 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
4184 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
4185 1.0.17 10 10017 12.so.0.1.0.17
4186 1.2.7 13 10207 12.so.0.1.2.7
4187 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
4188 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
4189 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
4190 1.0.18 10 10018 12.so.0.1.0.18
4191 1.2.8 13 10208 12.so.0.1.2.8
4192 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
4193 1.2.9beta4-11 13 10209 12.so.0.9[.0]
4194 1.2.9rc1 13 10209 12.so.0.9[.0]
4195 1.2.9 13 10209 12.so.0.9[.0]
4196 1.2.10beta1-7 13 10210 12.so.0.10[.0]
4197 1.2.10rc1-2 13 10210 12.so.0.10[.0]
4198 1.2.10 13 10210 12.so.0.10[.0]
4199 1.4.0beta1-6 14 10400 14.so.0.0[.0]
4200 1.2.11beta1-4 13 10210 12.so.0.11[.0]
4201 1.4.0beta7-8 14 10400 14.so.0.0[.0]
4202 1.2.11 13 10211 12.so.0.11[.0]
4203 1.2.12 13 10212 12.so.0.12[.0]
4204 1.4.0beta9-14 14 10400 14.so.0.0[.0]
4205 1.2.13 13 10213 12.so.0.13[.0]
4206 1.4.0beta15-36 14 10400 14.so.0.0[.0]
4207 1.4.0beta37-87 14 10400 14.so.14.0[.0]
4208 1.4.0rc01 14 10400 14.so.14.0[.0]
4209 1.4.0beta88-109 14 10400 14.so.14.0[.0]
4210 1.4.0rc02-08 14 10400 14.so.14.0[.0]
4211 1.4.0 14 10400 14.so.14.0[.0]
4212 1.4.1beta01-03 14 10401 14.so.14.1[.0]
4213 1.4.1rc01 14 10401 14.so.14.1[.0]
4214 1.4.1beta04-12 14 10401 14.so.14.1[.0]
4215 1.4.1rc02-04 14 10401 14.so.14.1[.0]
4216 1.4.1 14 10401 14.so.14.1[.0]
4218 Henceforth the source version will match the shared-library minor
4219 and patch numbers; the shared-library major version number will be
4220 used for changes in backward compatibility, as it is intended. The
4221 PNG_PNGLIB_VER macro, which is not used within libpng but is available
4222 for applications, is an unsigned integer of the form xyyzz corresponding
4223 to the source version x.y.z (leading zeros in y and z). Beta versions
4224 were given the previous public release number plus a letter, until
4225 version 1.0.6j; from then on they were given the upcoming public
4226 release number plus "betaNN" or "rcN".
4233 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
4234 http://www.libpng.org/pub/png
4239 (generally) at the same location as
4243 ftp://ftp.info-zip.org/pub/infozip/zlib
4246 .IR PNG specification: RFC 2083
4248 (generally) at the same location as
4252 ftp://ds.internic.net/rfc/rfc2083.txt
4254 or (as a W3C Recommendation) at
4256 http://www.w3.org/TR/REC-png.html
4259 In the case of any inconsistency between the PNG specification
4260 and this library, the specification takes precedence.
4263 This man page: Glenn Randers-Pehrson
4264 <glennrp at users.sourceforge.net>
4266 The contributing authors would like to thank all those who helped
4267 with testing, bug fixes, and patience. This wouldn't have been
4268 possible without all of you.
4270 Thanks to Frank J. T. Wojcik for helping with the documentation.
4272 Libpng version 1.4.1 - February 25, 2010:
4273 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
4274 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
4276 Supported by the PNG development group
4278 png-mng-implement at lists.sf.net
4279 (subscription required; visit
4280 png-mng-implement at lists.sourceforge.net (subscription required; visit
4281 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
4284 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
4286 (This copy of the libpng notices is provided for your convenience. In case of
4287 any discrepancy between this copy and the notices in the file png.h that is
4288 included in the libpng distribution, the latter shall prevail.)
4290 If you modify libpng you may insert additional notices immediately following
4293 This code is released under the libpng license.
4295 libpng versions 1.2.6, August 15, 2004, through 1.4.1, February 25, 2010, are
4296 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
4297 distributed according to the same disclaimer and license as libpng-1.2.5
4298 with the following individual added to the list of Contributing Authors
4302 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
4303 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
4304 distributed according to the same disclaimer and license as libpng-1.0.6
4305 with the following individuals added to the list of Contributing Authors
4307 Simon-Pierre Cadieux
4311 and with the following additions to the disclaimer:
4313 There is no warranty against interference with your
4314 enjoyment of the library or against infringement.
4315 There is no warranty that our efforts or the library
4316 will fulfill any of your particular purposes or needs.
4317 This library is provided with all faults, and the entire
4318 risk of satisfactory quality, performance, accuracy, and
4319 effort is with the user.
4321 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
4322 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
4323 Distributed according to the same disclaimer and license as libpng-0.96,
4324 with the following individuals added to the list of Contributing Authors:
4327 Glenn Randers-Pehrson
4330 libpng versions 0.89, June 1996, through 0.96, May 1997, are
4331 Copyright (c) 1996, 1997 Andreas Dilger
4332 Distributed according to the same disclaimer and license as libpng-0.88,
4333 with the following individuals added to the list of Contributing Authors:
4342 libpng versions 0.5, May 1995, through 0.88, January 1996, are
4343 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
4345 For the purposes of this copyright and license, "Contributing Authors"
4346 is defined as the following set of individuals:
4354 The PNG Reference Library is supplied "AS IS". The Contributing Authors
4355 and Group 42, Inc. disclaim all warranties, expressed or implied,
4356 including, without limitation, the warranties of merchantability and of
4357 fitness for any purpose. The Contributing Authors and Group 42, Inc.
4358 assume no liability for direct, indirect, incidental, special, exemplary,
4359 or consequential damages, which may result from the use of the PNG
4360 Reference Library, even if advised of the possibility of such damage.
4362 Permission is hereby granted to use, copy, modify, and distribute this
4363 source code, or portions hereof, for any purpose, without fee, subject
4364 to the following restrictions:
4366 1. The origin of this source code must not be misrepresented.
4368 2. Altered versions must be plainly marked as such and
4369 must not be misrepresented as being the original source.
4371 3. This Copyright notice may not be removed or altered from
4372 any source or altered source distribution.
4374 The Contributing Authors and Group 42, Inc. specifically permit, without
4375 fee, and encourage the use of this source code as a component to
4376 supporting the PNG file format in commercial products. If you use this
4377 source code in a product, acknowledgment is not required but would be
4381 A "png_get_copyright" function is available, for convenient use in "about"
4384 printf("%s",png_get_copyright(NULL));
4386 Also, the PNG logo (in PNG format, of course) is supplied in the
4387 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4389 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4390 certification mark of the Open Source Initiative.
4392 Glenn Randers-Pehrson
4393 glennrp at users.sourceforge.net
projects / lugaru.git / blob