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assert if ShowModal() is called after a previous Show() (#1416)
[wxWidgets.git] / src / png / libpng.3
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0272a10d
VZ		 1.TH LIBPNG 3 "September 8, 2007"
2.SH NAME
3libpng \- Portable Network Graphics (PNG) Reference Library 1.2.20
4.SH SYNOPSIS
5\fB
6#include <png.h>\fP
7
8\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
9
10\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
11
12\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
13
14\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
15
16\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
17
18\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
19
20\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
21
22\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
23
24\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
25
26\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
27
28\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
29
30\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
31
32\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
33
34\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
35
36\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
37
38\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
39
40\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
41
42\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
43
44\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
45
46\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
47
48\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
49
50\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
51
52\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
53
54\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
55
56\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
57
58\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
59
60\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
61
62\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
63
64\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
65
66\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
67
68\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
69
70\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
71
72\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
73
74\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
75
76\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
77
78\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
79
80\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
81
82\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
83
84\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
85
86\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
87
88\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
89
90\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
91
92\fB#if !defined(PNG_1_0_X) png_int_32 png_get_int_32 (png_bytep buf); \fI#endif
93
94\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
95
96\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
97
98\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
99
100\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
101
102\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
103
104\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
105
106\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
107
108\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
109
110\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
111
112\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
113
114\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
115
116\fBpng_byte png_get_rgb_to_gray_status (png_structp png_ptr) png_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
117
118\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
119
120\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
121
122\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
123
124\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
125
126\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
127
128\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
129
130\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
131
132\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_values\fP\fB);\fP
133
134\fB#if !defined(PNG_1_0_X) png_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
135
136\fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
137
138\fBpng_uint_32 png_get_uint_32 (png_bytep buf); \fI#endif
139
140\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
141
142\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
143
144\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
145
146\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
147
148\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
149
150\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
151
152\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
153
154\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
155
156\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
157
158\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
159
160\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
161
162\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
163
164\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
165
166\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
167
168\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
169
170\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
171
172\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
173
174\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
175
176\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
177
178\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
179
180\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
181
182\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
183
184\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
185
186\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
187
188\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
189
190\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
191
192\fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
193
194\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
195
196\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
197
198\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
199
200\fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
201
202\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
203
204\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
205
206\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
207
208\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
209
210\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
211
212\fB#if !defined(PNG_1_0_X) png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
213
214\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
215
216\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
217
218\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int flags); \fI#endif
219
220\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
221
222\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
223
224\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
225
226\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
227
228\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
229
230\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
231
232\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
233
234\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
235
236\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
237
238\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
239
240\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
241
242\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
243
244\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
245
246\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
247
248\fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
249
250\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
251
252\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
253
254\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
255
256\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
257
258\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
259
260\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
261
262\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
263
264\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
265
266\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
267
268\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
269
270\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
271
272\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
273
274\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
275
276\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
277
278\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
279
280\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
281
282\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
283
284\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
285
286\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
287
288\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
289
290\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
291
292\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
293
294\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
295
296\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
297
298\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
299
300\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
301
302\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
303
304\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
305
306\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
307
308\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
309
310\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
311
312\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
313
314\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
315
316\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
317
318\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
319
320\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
321
322\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
323
324\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
325
326\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
327
328\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
329
330\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
331
332\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
333
334\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
335
336\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
337
338\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
339
340\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_values\fP\fB);\fP
341
342\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
343
344\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
345
346\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
347
348\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
349
350\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
351
352\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
353
354\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
355
356\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
357
358\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
359
360\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
361
362\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
363
364\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
365
366\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
367
368\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
369
370\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
371
372\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
373
374\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
375
376\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
377
378\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
379
380\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
381
382\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
383
384\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
385
386\fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
387
388\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
389
390\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
391
392\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
393
394\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
395
396\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
397
398\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
399
400\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
401
402.SH DESCRIPTION
403The
404.I libpng
405library supports encoding, decoding, and various manipulations of
406the Portable Network Graphics (PNG) format image files. It uses the
407.IR zlib(3)
408compression library.
409Following is a copy of the libpng.txt file that accompanies libpng.
410.SH LIBPNG.TXT
411libpng.txt - A description on how to use and modify libpng
412
413 libpng version 1.2.20 - September 8, 2007
414 Updated and distributed by Glenn Randers-Pehrson
415 <glennrp at users.sourceforge.net>
416 Copyright (c) 1998-2007 Glenn Randers-Pehrson
417 For conditions of distribution and use, see copyright
418 notice in png.h.
419
420 based on:
421
422 libpng 1.0 beta 6 version 0.96 May 28, 1997
423 Updated and distributed by Andreas Dilger
424 Copyright (c) 1996, 1997 Andreas Dilger
425
426 libpng 1.0 beta 2 - version 0.88 January 26, 1996
427 For conditions of distribution and use, see copyright
428 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
429 Schalnat, Group 42, Inc.
430
431 Updated/rewritten per request in the libpng FAQ
432 Copyright (c) 1995, 1996 Frank J. T. Wojcik
433 December 18, 1995 & January 20, 1996
434
435.SH I. Introduction
436
437This file describes how to use and modify the PNG reference library
438(known as libpng) for your own use. There are five sections to this
439file: introduction, structures, reading, writing, and modification and
440configuration notes for various special platforms. In addition to this
441file, example.c is a good starting point for using the library, as
442it is heavily commented and should include everything most people
443will need. We assume that libpng is already installed; see the
444INSTALL file for instructions on how to install libpng.
445
446For examples of libpng usage, see the files "example.c", "pngtest.c",
447and the files in the "contrib" directory, all of which are included in the
448libpng distribution.
449
450Libpng was written as a companion to the PNG specification, as a way
451of reducing the amount of time and effort it takes to support the PNG
452file format in application programs.
453
454The PNG specification (second edition), November 2003, is available as
455a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
456<http://www.w3.org/TR/2003/REC-PNG-20031110/
457The W3C and ISO documents have identical technical content.
458
459The PNG-1.2 specification is available at
460<http://www.libpng.org/pub/png/documents/>
461
462The PNG-1.0 specification is available
463as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
464W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
465additional chunks are described in the special-purpose public chunks
466documents at <http://www.libpng.org/pub/png/documents/>.
467
468Other information
469about PNG, and the latest version of libpng, can be found at the PNG home
470page, <http://www.libpng.org/pub/png/>.
471
472Most users will not have to modify the library significantly; advanced
473users may want to modify it more. All attempts were made to make it as
474complete as possible, while keeping the code easy to understand.
475Currently, this library only supports C. Support for other languages
476is being considered.
477
478Libpng has been designed to handle multiple sessions at one time,
479to be easily modifiable, to be portable to the vast majority of
480machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
481to use. The ultimate goal of libpng is to promote the acceptance of
482the PNG file format in whatever way possible. While there is still
483work to be done (see the TODO file), libpng should cover the
484majority of the needs of its users.
485
486Libpng uses zlib for its compression and decompression of PNG files.
487Further information about zlib, and the latest version of zlib, can
488be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
489The zlib compression utility is a general purpose utility that is
490useful for more than PNG files, and can be used without libpng.
491See the documentation delivered with zlib for more details.
492You can usually find the source files for the zlib utility wherever you
493find the libpng source files.
494
495Libpng is thread safe, provided the threads are using different
496instances of the structures. Each thread should have its own
497png_struct and png_info instances, and thus its own image.
498Libpng does not protect itself against two threads using the
499same instance of a structure.
500
501.SH II. Structures
502
503There are two main structures that are important to libpng, png_struct
504and png_info. The first, png_struct, is an internal structure that
505will not, for the most part, be used by a user except as the first
506variable passed to every libpng function call.
507
508The png_info structure is designed to provide information about the
509PNG file. At one time, the fields of png_info were intended to be
510directly accessible to the user. However, this tended to cause problems
511with applications using dynamically loaded libraries, and as a result
512a set of interface functions for png_info (the png_get_*() and png_set_*()
513functions) was developed. The fields of png_info are still available for
514older applications, but it is suggested that applications use the new
515interfaces if at all possible.
516
517Applications that do make direct access to the members of png_struct (except
518for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
519and applications that make direct access to the members of png_info must
520be recompiled if they were compiled or loaded with libpng version 1.0.6,
521in which the members were in a different order. In version 1.0.7, the
522members of the png_info structure reverted to the old order, as they were
523in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
524structures are going to be hidden, and the contents of the structures will
525only be accessible through the png_get/png_set functions.
526
527The png.h header file is an invaluable reference for programming with libpng.
528And while I'm on the topic, make sure you include the libpng header file:
529
530#include <png.h>
531
532.SH III. Reading
533
534We'll now walk you through the possible functions to call when reading
535in a PNG file sequentially, briefly explaining the syntax and purpose
536of each one. See example.c and png.h for more detail. While
537progressive reading is covered in the next section, you will still
538need some of the functions discussed in this section to read a PNG
539file.
540
541.SS Setup
542
543You will want to do the I/O initialization(*) before you get into libpng,
544so if it doesn't work, you don't have much to undo. Of course, you
545will also want to insure that you are, in fact, dealing with a PNG
546file. Libpng provides a simple check to see if a file is a PNG file.
547To use it, pass in the first 1 to 8 bytes of the file to the function
548png_sig_cmp(), and it will return 0 if the bytes match the corresponding
549bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
550you pass in, the greater the accuracy of the prediction.
551
552If you are intending to keep the file pointer open for use in libpng,
553you must ensure you don't read more than 8 bytes from the beginning
554of the file, and you also have to make a call to png_set_sig_bytes_read()
555with the number of bytes you read from the beginning. Libpng will
556then only check the bytes (if any) that your program didn't read.
557
558(*): If you are not using the standard I/O functions, you will need
559to replace them with custom functions. See the discussion under
560Customizing libpng.
561
562
563 FILE *fp = fopen(file_name, "rb");
564 if (!fp)
565 {
566 return (ERROR);
567 }
568 fread(header, 1, number, fp);
569 is_png = !png_sig_cmp(header, 0, number);
570 if (!is_png)
571 {
572 return (NOT_PNG);
573 }
574
575
576Next, png_struct and png_info need to be allocated and initialized. In
577order to ensure that the size of these structures is correct even with a
578dynamically linked libpng, there are functions to initialize and
579allocate the structures. We also pass the library version, optional
580pointers to error handling functions, and a pointer to a data struct for
581use by the error functions, if necessary (the pointer and functions can
582be NULL if the default error handlers are to be used). See the section
583on Changes to Libpng below regarding the old initialization functions.
584The structure allocation functions quietly return NULL if they fail to
585create the structure, so your application should check for that.
586
587 png_structp png_ptr = png_create_read_struct
588 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
589 user_error_fn, user_warning_fn);
590 if (!png_ptr)
591 return (ERROR);
592
593 png_infop info_ptr = png_create_info_struct(png_ptr);
594 if (!info_ptr)
595 {
596 png_destroy_read_struct(&png_ptr,
597 (png_infopp)NULL, (png_infopp)NULL);
598 return (ERROR);
599 }
600
601 png_infop end_info = png_create_info_struct(png_ptr);
602 if (!end_info)
603 {
604 png_destroy_read_struct(&png_ptr, &info_ptr,
605 (png_infopp)NULL);
606 return (ERROR);
607 }
608
609If you want to use your own memory allocation routines,
610define PNG_USER_MEM_SUPPORTED and use
611png_create_read_struct_2() instead of png_create_read_struct():
612
613 png_structp png_ptr = png_create_read_struct_2
614 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
615 user_error_fn, user_warning_fn, (png_voidp)
616 user_mem_ptr, user_malloc_fn, user_free_fn);
617
618The error handling routines passed to png_create_read_struct()
619and the memory alloc/free routines passed to png_create_struct_2()
620are only necessary if you are not using the libpng supplied error
621handling and memory alloc/free functions.
622
623When libpng encounters an error, it expects to longjmp back
624to your routine. Therefore, you will need to call setjmp and pass
625your png_jmpbuf(png_ptr). If you read the file from different
626routines, you will need to update the jmpbuf field every time you enter
627a new routine that will call a png_*() function.
628
629See your documentation of setjmp/longjmp for your compiler for more
630information on setjmp/longjmp. See the discussion on libpng error
631handling in the Customizing Libpng section below for more information
632on the libpng error handling. If an error occurs, and libpng longjmp's
633back to your setjmp, you will want to call png_destroy_read_struct() to
634free any memory.
635
636 if (setjmp(png_jmpbuf(png_ptr)))
637 {
638 png_destroy_read_struct(&png_ptr, &info_ptr,
639 &end_info);
640 fclose(fp);
641 return (ERROR);
642 }
643
644If you would rather avoid the complexity of setjmp/longjmp issues,
645you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
646errors will result in a call to PNG_ABORT() which defaults to abort().
647
648Now you need to set up the input code. The default for libpng is to
649use the C function fread(). If you use this, you will need to pass a
650valid FILE * in the function png_init_io(). Be sure that the file is
651opened in binary mode. If you wish to handle reading data in another
652way, you need not call the png_init_io() function, but you must then
653implement the libpng I/O methods discussed in the Customizing Libpng
654section below.
655
656 png_init_io(png_ptr, fp);
657
658If you had previously opened the file and read any of the signature from
659the beginning in order to see if this was a PNG file, you need to let
660libpng know that there are some bytes missing from the start of the file.
661
662 png_set_sig_bytes(png_ptr, number);
663
664.SS Setting up callback code
665
666You can set up a callback function to handle any unknown chunks in the
667input stream. You must supply the function
668
669 read_chunk_callback(png_ptr ptr,
670 png_unknown_chunkp chunk);
671 {
672 /* The unknown chunk structure contains your
673 chunk data: */
674 png_byte name[5];
675 png_byte *data;
676 png_size_t size;
677 /* Note that libpng has already taken care of
678 the CRC handling */
679
680 /* put your code here. Return one of the
681 following: */
682
683 return (-n); /* chunk had an error */
684 return (0); /* did not recognize */
685 return (n); /* success */
686 }
687
688(You can give your function another name that you like instead of
689"read_chunk_callback")
690
691To inform libpng about your function, use
692
693 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
694 read_chunk_callback);
695
696This names not only the callback function, but also a user pointer that
697you can retrieve with
698
699 png_get_user_chunk_ptr(png_ptr);
700
701At this point, you can set up a callback function that will be
702called after each row has been read, which you can use to control
703a progress meter or the like. It's demonstrated in pngtest.c.
704You must supply a function
705
706 void read_row_callback(png_ptr ptr, png_uint_32 row,
707 int pass);
708 {
709 /* put your code here */
710 }
711
712(You can give it another name that you like instead of "read_row_callback")
713
714To inform libpng about your function, use
715
716 png_set_read_status_fn(png_ptr, read_row_callback);
717
718.SS Width and height limits
719
720The PNG specification allows the width and height of an image to be as
721large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
722Since very few applications really need to process such large images,
723we have imposed an arbitrary 1-million limit on rows and columns.
724Larger images will be rejected immediately with a png_error() call. If
725you wish to override this limit, you can use
726
727 png_set_user_limits(png_ptr, width_max, height_max);
728
729to set your own limits, or use width_max = height_max = 0x7fffffffL
730to allow all valid dimensions (libpng may reject some very large images
731anyway because of potential buffer overflow conditions).
732
733You should put this statement after you create the PNG structure and
734before calling png_read_info(), png_read_png(), or png_process_data().
735If you need to retrieve the limits that are being applied, use
736
737 width_max = png_get_user_width_max(png_ptr);
738 height_max = png_get_user_height_max(png_ptr);
739
740.SS Unknown-chunk handling
741
742Now you get to set the way the library processes unknown chunks in the
743input PNG stream. Both known and unknown chunks will be read. Normal
744behavior is that known chunks will be parsed into information in
745various info_ptr members; unknown chunks will be discarded. To change
746this, you can call:
747
748 png_set_keep_unknown_chunks(png_ptr, keep,
749 chunk_list, num_chunks);
750 keep - 0: do not handle as unknown
751 1: do not keep
752 2: keep only if safe-to-copy
753 3: keep even if unsafe-to-copy
754 You can use these definitions:
755 PNG_HANDLE_CHUNK_AS_DEFAULT 0
756 PNG_HANDLE_CHUNK_NEVER 1
757 PNG_HANDLE_CHUNK_IF_SAFE 2
758 PNG_HANDLE_CHUNK_ALWAYS 3
759 chunk_list - list of chunks affected (a byte string,
760 five bytes per chunk, NULL or '\0' if
761 num_chunks is 0)
762 num_chunks - number of chunks affected; if 0, all
763 unknown chunks are affected. If nonzero,
764 only the chunks in the list are affected
765
766Unknown chunks declared in this way will be saved as raw data onto a
767list of png_unknown_chunk structures. If a chunk that is normally
768known to libpng is named in the list, it will be handled as unknown,
769according to the "keep" directive. If a chunk is named in successive
770instances of png_set_keep_unknown_chunks(), the final instance will
771take precedence. The IHDR and IEND chunks should not be named in
772chunk_list; if they are, libpng will process them normally anyway.
773
774.SS The high-level read interface
775
776At this point there are two ways to proceed; through the high-level
777read interface, or through a sequence of low-level read operations.
778You can use the high-level interface if (a) you are willing to read
779the entire image into memory, and (b) the input transformations
780you want to do are limited to the following set:
781
782 PNG_TRANSFORM_IDENTITY No transformation
783 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
784 8 bits
785 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
786 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
787 samples to bytes
788 PNG_TRANSFORM_PACKSWAP Change order of packed
789 pixels to LSB first
790 PNG_TRANSFORM_EXPAND Perform set_expand()
791 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
792 PNG_TRANSFORM_SHIFT Normalize pixels to the
793 sBIT depth
794 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
795 to BGRA
796 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
797 to AG
798 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
799 to transparency
800 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
801
802(This excludes setting a background color, doing gamma transformation,
803dithering, and setting filler.) If this is the case, simply do this:
804
805 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
806
807where png_transforms is an integer containing the bitwise OR of
808some set of transformation flags. This call is equivalent to png_read_info(),
809followed the set of transformations indicated by the transform mask,
810then png_read_image(), and finally png_read_end().
811
812(The final parameter of this call is not yet used. Someday it might point
813to transformation parameters required by some future input transform.)
814
815You must use png_transforms and not call any png_set_transform() functions
816when you use png_read_png().
817
818After you have called png_read_png(), you can retrieve the image data
819with
820
821 row_pointers = png_get_rows(png_ptr, info_ptr);
822
823where row_pointers is an array of pointers to the pixel data for each row:
824
825 png_bytep row_pointers[height];
826
827If you know your image size and pixel size ahead of time, you can allocate
828row_pointers prior to calling png_read_png() with
829
830 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
831 png_error (png_ptr,
832 "Image is too tall to process in memory");
833 if (width > PNG_UINT_32_MAX/pixel_size)
834 png_error (png_ptr,
835 "Image is too wide to process in memory");
836 row_pointers = png_malloc(png_ptr,
837 height*png_sizeof(png_bytep));
838 for (int i=0; i<height, i++)
839 row_pointers[i]=png_malloc(png_ptr,
840 width*pixel_size);
841 png_set_rows(png_ptr, info_ptr, &row_pointers);
842
843Alternatively you could allocate your image in one big block and define
844row_pointers[i] to point into the proper places in your block.
845
846If you use png_set_rows(), the application is responsible for freeing
847row_pointers (and row_pointers[i], if they were separately allocated).
848
849If you don't allocate row_pointers ahead of time, png_read_png() will
850do it, and it'll be free'ed when you call png_destroy_*().
851
852.SS The low-level read interface
853
854If you are going the low-level route, you are now ready to read all
855the file information up to the actual image data. You do this with a
856call to png_read_info().
857
858 png_read_info(png_ptr, info_ptr);
859
860This will process all chunks up to but not including the image data.
861
862.SS Querying the info structure
863
864Functions are used to get the information from the info_ptr once it
865has been read. Note that these fields may not be completely filled
866in until png_read_end() has read the chunk data following the image.
867
868 png_get_IHDR(png_ptr, info_ptr, &width, &height,
869 &bit_depth, &color_type, &interlace_type,
870 &compression_type, &filter_method);
871
872 width - holds the width of the image
873 in pixels (up to 2^31).
874 height - holds the height of the image
875 in pixels (up to 2^31).
876 bit_depth - holds the bit depth of one of the
877 image channels. (valid values are
878 1, 2, 4, 8, 16 and depend also on
879 the color_type. See also
880 significant bits (sBIT) below).
881 color_type - describes which color/alpha channels
882 are present.
883 PNG_COLOR_TYPE_GRAY
884 (bit depths 1, 2, 4, 8, 16)
885 PNG_COLOR_TYPE_GRAY_ALPHA
886 (bit depths 8, 16)
887 PNG_COLOR_TYPE_PALETTE
888 (bit depths 1, 2, 4, 8)
889 PNG_COLOR_TYPE_RGB
890 (bit_depths 8, 16)
891 PNG_COLOR_TYPE_RGB_ALPHA
892 (bit_depths 8, 16)
893
894 PNG_COLOR_MASK_PALETTE
895 PNG_COLOR_MASK_COLOR
896 PNG_COLOR_MASK_ALPHA
897
898 filter_method - (must be PNG_FILTER_TYPE_BASE
899 for PNG 1.0, and can also be
900 PNG_INTRAPIXEL_DIFFERENCING if
901 the PNG datastream is embedded in
902 a MNG-1.0 datastream)
903 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
904 for PNG 1.0)
905 interlace_type - (PNG_INTERLACE_NONE or
906 PNG_INTERLACE_ADAM7)
907 Any or all of interlace_type, compression_type, of
908 filter_method can be NULL if you are
909 not interested in their values.
910
911 channels = png_get_channels(png_ptr, info_ptr);
912 channels - number of channels of info for the
913 color type (valid values are 1 (GRAY,
914 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
915 4 (RGB_ALPHA or RGB + filler byte))
916 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
917 rowbytes - number of bytes needed to hold a row
918
919 signature = png_get_signature(png_ptr, info_ptr);
920 signature - holds the signature read from the
921 file (if any). The data is kept in
922 the same offset it would be if the
923 whole signature were read (i.e. if an
924 application had already read in 4
925 bytes of signature before starting
926 libpng, the remaining 4 bytes would
927 be in signature[4] through signature[7]
928 (see png_set_sig_bytes())).
929
930
931 width = png_get_image_width(png_ptr,
932 info_ptr);
933 height = png_get_image_height(png_ptr,
934 info_ptr);
935 bit_depth = png_get_bit_depth(png_ptr,
936 info_ptr);
937 color_type = png_get_color_type(png_ptr,
938 info_ptr);
939 filter_method = png_get_filter_type(png_ptr,
940 info_ptr);
941 compression_type = png_get_compression_type(png_ptr,
942 info_ptr);
943 interlace_type = png_get_interlace_type(png_ptr,
944 info_ptr);
945
946
947These are also important, but their validity depends on whether the chunk
948has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
949png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
950data has been read, or zero if it is missing. The parameters to the
951png_get_<chunk> are set directly if they are simple data types, or a pointer
952into the info_ptr is returned for any complex types.
953
954 png_get_PLTE(png_ptr, info_ptr, &palette,
955 &num_palette);
956 palette - the palette for the file
957 (array of png_color)
958 num_palette - number of entries in the palette
959
960 png_get_gAMA(png_ptr, info_ptr, &gamma);
961 gamma - the gamma the file is written
962 at (PNG_INFO_gAMA)
963
964 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
965 srgb_intent - the rendering intent (PNG_INFO_sRGB)
966 The presence of the sRGB chunk
967 means that the pixel data is in the
968 sRGB color space. This chunk also
969 implies specific values of gAMA and
970 cHRM.
971
972 png_get_iCCP(png_ptr, info_ptr, &name,
973 &compression_type, &profile, &proflen);
974 name - The profile name.
975 compression - The compression type; always
976 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
977 You may give NULL to this argument to
978 ignore it.
979 profile - International Color Consortium color
980 profile data. May contain NULs.
981 proflen - length of profile data in bytes.
982
983 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
984 sig_bit - the number of significant bits for
985 (PNG_INFO_sBIT) each of the gray,
986 red, green, and blue channels,
987 whichever are appropriate for the
988 given color type (png_color_16)
989
990 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
991 &trans_values);
992 trans - array of transparent entries for
993 palette (PNG_INFO_tRNS)
994 trans_values - graylevel or color sample values of
995 the single transparent color for
996 non-paletted images (PNG_INFO_tRNS)
997 num_trans - number of transparent entries
998 (PNG_INFO_tRNS)
999
1000 png_get_hIST(png_ptr, info_ptr, &hist);
1001 (PNG_INFO_hIST)
1002 hist - histogram of palette (array of
1003 png_uint_16)
1004
1005 png_get_tIME(png_ptr, info_ptr, &mod_time);
1006 mod_time - time image was last modified
1007 (PNG_VALID_tIME)
1008
1009 png_get_bKGD(png_ptr, info_ptr, &background);
1010 background - background color (PNG_VALID_bKGD)
1011 valid 16-bit red, green and blue
1012 values, regardless of color_type
1013
1014 num_comments = png_get_text(png_ptr, info_ptr,
1015 &text_ptr, &num_text);
1016 num_comments - number of comments
1017 text_ptr - array of png_text holding image
1018 comments
1019 text_ptr[i].compression - type of compression used
1020 on "text" PNG_TEXT_COMPRESSION_NONE
1021 PNG_TEXT_COMPRESSION_zTXt
1022 PNG_ITXT_COMPRESSION_NONE
1023 PNG_ITXT_COMPRESSION_zTXt
1024 text_ptr[i].key - keyword for comment. Must contain
1025 1-79 characters.
1026 text_ptr[i].text - text comments for current
1027 keyword. Can be empty.
1028 text_ptr[i].text_length - length of text string,
1029 after decompression, 0 for iTXt
1030 text_ptr[i].itxt_length - length of itxt string,
1031 after decompression, 0 for tEXt/zTXt
1032 text_ptr[i].lang - language of comment (empty
1033 string for unknown).
1034 text_ptr[i].lang_key - keyword in UTF-8
1035 (empty string for unknown).
1036 num_text - number of comments (same as
1037 num_comments; you can put NULL here
1038 to avoid the duplication)
1039 Note while png_set_text() will accept text, language,
1040 and translated keywords that can be NULL pointers, the
1041 structure returned by png_get_text will always contain
1042 regular zero-terminated C strings. They might be
1043 empty strings but they will never be NULL pointers.
1044
1045 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1046 &palette_ptr);
1047 palette_ptr - array of palette structures holding
1048 contents of one or more sPLT chunks
1049 read.
1050 num_spalettes - number of sPLT chunks read.
1051
1052 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1053 &unit_type);
1054 offset_x - positive offset from the left edge
1055 of the screen
1056 offset_y - positive offset from the top edge
1057 of the screen
1058 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1059
1060 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1061 &unit_type);
1062 res_x - pixels/unit physical resolution in
1063 x direction
1064 res_y - pixels/unit physical resolution in
1065 x direction
1066 unit_type - PNG_RESOLUTION_UNKNOWN,
1067 PNG_RESOLUTION_METER
1068
1069 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1070 &height)
1071 unit - physical scale units (an integer)
1072 width - width of a pixel in physical scale units
1073 height - height of a pixel in physical scale units
1074 (width and height are doubles)
1075
1076 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1077 &height)
1078 unit - physical scale units (an integer)
1079 width - width of a pixel in physical scale units
1080 height - height of a pixel in physical scale units
1081 (width and height are strings like "2.54")
1082
1083 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1084 info_ptr, &unknowns)
1085 unknowns - array of png_unknown_chunk
1086 structures holding unknown chunks
1087 unknowns[i].name - name of unknown chunk
1088 unknowns[i].data - data of unknown chunk
1089 unknowns[i].size - size of unknown chunk's data
1090 unknowns[i].location - position of chunk in file
1091
1092 The value of "i" corresponds to the order in which the
1093 chunks were read from the PNG file or inserted with the
1094 png_set_unknown_chunks() function.
1095
1096The data from the pHYs chunk can be retrieved in several convenient
1097forms:
1098
1099 res_x = png_get_x_pixels_per_meter(png_ptr,
1100 info_ptr)
1101 res_y = png_get_y_pixels_per_meter(png_ptr,
1102 info_ptr)
1103 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1104 info_ptr)
1105 res_x = png_get_x_pixels_per_inch(png_ptr,
1106 info_ptr)
1107 res_y = png_get_y_pixels_per_inch(png_ptr,
1108 info_ptr)
1109 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1110 info_ptr)
1111 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1112 info_ptr)
1113
1114 (Each of these returns 0 [signifying "unknown"] if
1115 the data is not present or if res_x is 0;
1116 res_x_and_y is 0 if res_x != res_y)
1117
1118The data from the oFFs chunk can be retrieved in several convenient
1119forms:
1120
1121 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1122 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1123 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1124 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1125
1126 (Each of these returns 0 [signifying "unknown" if both
1127 x and y are 0] if the data is not present or if the
1128 chunk is present but the unit is the pixel)
1129
1130For more information, see the png_info definition in png.h and the
1131PNG specification for chunk contents. Be careful with trusting
1132rowbytes, as some of the transformations could increase the space
1133needed to hold a row (expand, filler, gray_to_rgb, etc.).
1134See png_read_update_info(), below.
1135
1136A quick word about text_ptr and num_text. PNG stores comments in
1137keyword/text pairs, one pair per chunk, with no limit on the number
1138of text chunks, and a 2^31 byte limit on their size. While there are
1139suggested keywords, there is no requirement to restrict the use to these
1140strings. It is strongly suggested that keywords and text be sensible
1141to humans (that's the point), so don't use abbreviations. Non-printing
1142symbols are not allowed. See the PNG specification for more details.
1143There is also no requirement to have text after the keyword.
1144
1145Keywords should be limited to 79 Latin-1 characters without leading or
1146trailing spaces, but non-consecutive spaces are allowed within the
1147keyword. It is possible to have the same keyword any number of times.
1148The text_ptr is an array of png_text structures, each holding a
1149pointer to a language string, a pointer to a keyword and a pointer to
1150a text string. The text string, language code, and translated
1151keyword may be empty or NULL pointers. The keyword/text
1152pairs are put into the array in the order that they are received.
1153However, some or all of the text chunks may be after the image, so, to
1154make sure you have read all the text chunks, don't mess with these
1155until after you read the stuff after the image. This will be
1156mentioned again below in the discussion that goes with png_read_end().
1157
1158.SS Input transformations
1159
1160After you've read the header information, you can set up the library
1161to handle any special transformations of the image data. The various
1162ways to transform the data will be described in the order that they
1163should occur. This is important, as some of these change the color
1164type and/or bit depth of the data, and some others only work on
1165certain color types and bit depths. Even though each transformation
1166checks to see if it has data that it can do something with, you should
1167make sure to only enable a transformation if it will be valid for the
1168data. For example, don't swap red and blue on grayscale data.
1169
1170The colors used for the background and transparency values should be
1171supplied in the same format/depth as the current image data. They
1172are stored in the same format/depth as the image data in a bKGD or tRNS
1173chunk, so this is what libpng expects for this data. The colors are
1174transformed to keep in sync with the image data when an application
1175calls the png_read_update_info() routine (see below).
1176
1177Data will be decoded into the supplied row buffers packed into bytes
1178unless the library has been told to transform it into another format.
1179For example, 4 bit/pixel paletted or grayscale data will be returned
11802 pixels/byte with the leftmost pixel in the high-order bits of the
1181byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1182in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1183is called to insert filler bytes, either before or after each RGB triplet.
118416-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1185byte of the color value first, unless png_set_strip_16() is called to
1186transform it to regular RGB RGB triplets, or png_set_filler() or
1187png_set_add alpha() is called to insert filler bytes, either before or
1188after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1189be modified with
1190png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1191
1192The following code transforms grayscale images of less than 8 to 8 bits,
1193changes paletted images to RGB, and adds a full alpha channel if there is
1194transparency information in a tRNS chunk. This is most useful on
1195grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1196viewing application that wishes to treat all images in the same way.
1197
1198 if (color_type == PNG_COLOR_TYPE_PALETTE)
1199 png_set_palette_to_rgb(png_ptr);
1200
1201 if (color_type == PNG_COLOR_TYPE_GRAY &&
1202 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1203
1204 if (png_get_valid(png_ptr, info_ptr,
1205 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1206
1207These three functions are actually aliases for png_set_expand(), added
1208in libpng version 1.0.4, with the function names expanded to improve code
1209readability. In some future version they may actually do different
1210things.
1211
1212As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1213added. It expands the sample depth without changing tRNS to alpha.
1214At the same time, png_set_gray_1_2_4_to_8() was deprecated, and it
1215will be removed from a future version.
1216
1217PNG can have files with 16 bits per channel. If you only can handle
12188 bits per channel, this will strip the pixels down to 8 bit.
1219
1220 if (bit_depth == 16)
1221 png_set_strip_16(png_ptr);
1222
1223If, for some reason, you don't need the alpha channel on an image,
1224and you want to remove it rather than combining it with the background
1225(but the image author certainly had in mind that you *would* combine
1226it with the background, so that's what you should probably do):
1227
1228 if (color_type & PNG_COLOR_MASK_ALPHA)
1229 png_set_strip_alpha(png_ptr);
1230
1231In PNG files, the alpha channel in an image
1232is the level of opacity. If you need the alpha channel in an image to
1233be the level of transparency instead of opacity, you can invert the
1234alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1235fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1236images) is fully transparent, with
1237
1238 png_set_invert_alpha(png_ptr);
1239
1240PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1241they can, resulting in, for example, 8 pixels per byte for 1 bit
1242files. This code expands to 1 pixel per byte without changing the
1243values of the pixels:
1244
1245 if (bit_depth < 8)
1246 png_set_packing(png_ptr);
1247
1248PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1249stored in a PNG image have been "scaled" or "shifted" up to the next
1250higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
12518 bits/sample in the range [0, 255]). However, it is also possible to
1252convert the PNG pixel data back to the original bit depth of the image.
1253This call reduces the pixels back down to the original bit depth:
1254
1255 png_color_8p sig_bit;
1256
1257 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1258 png_set_shift(png_ptr, sig_bit);
1259
1260PNG files store 3-color pixels in red, green, blue order. This code
1261changes the storage of the pixels to blue, green, red:
1262
1263 if (color_type == PNG_COLOR_TYPE_RGB ||
1264 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1265 png_set_bgr(png_ptr);
1266
1267PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1268into 4 or 8 bytes for windowing systems that need them in this format:
1269
1270 if (color_type == PNG_COLOR_TYPE_RGB)
1271 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1272
1273where "filler" is the 8 or 16-bit number to fill with, and the location is
1274either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1275you want the filler before the RGB or after. This transformation
1276does not affect images that already have full alpha channels. To add an
1277opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1278will generate RGBA pixels.
1279
1280Note that png_set_filler() does not change the color type. If you want
1281to do that, you can add a true alpha channel with
1282
1283 if (color_type == PNG_COLOR_TYPE_RGB ||
1284 color_type == PNG_COLOR_TYPE_GRAY)
1285 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1286
1287where "filler" contains the alpha value to assign to each pixel.
1288This function was added in libpng-1.2.7.
1289
1290If you are reading an image with an alpha channel, and you need the
1291data as ARGB instead of the normal PNG format RGBA:
1292
1293 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1294 png_set_swap_alpha(png_ptr);
1295
1296For some uses, you may want a grayscale image to be represented as
1297RGB. This code will do that conversion:
1298
1299 if (color_type == PNG_COLOR_TYPE_GRAY ||
1300 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1301 png_set_gray_to_rgb(png_ptr);
1302
1303Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1304with alpha.
1305
1306 if (color_type == PNG_COLOR_TYPE_RGB ||
1307 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1308 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1309 int red_weight, int green_weight);
1310
1311 error_action = 1: silently do the conversion
1312 error_action = 2: issue a warning if the original
1313 image has any pixel where
1314 red != green or red != blue
1315 error_action = 3: issue an error and abort the
1316 conversion if the original
1317 image has any pixel where
1318 red != green or red != blue
1319
1320 red_weight: weight of red component times 100000
1321 green_weight: weight of green component times 100000
1322 If either weight is negative, default
1323 weights (21268, 71514) are used.
1324
1325If you have set error_action = 1 or 2, you can
1326later check whether the image really was gray, after processing
1327the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1328It will return a png_byte that is zero if the image was gray or
13291 if there were any non-gray pixels. bKGD and sBIT data
1330will be silently converted to grayscale, using the green channel
1331data, regardless of the error_action setting.
1332
1333With red_weight+green_weight<=100000,
1334the normalized graylevel is computed:
1335
1336 int rw = red_weight * 65536;
1337 int gw = green_weight * 65536;
1338 int bw = 65536 - (rw + gw);
1339 gray = (rw*red + gw*green + bw*blue)/65536;
1340
1341The default values approximate those recommended in the Charles
1342Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1343Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1344
1345 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1346
1347Libpng approximates this with
1348
1349 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1350
1351which can be expressed with integers as
1352
1353 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1354
1355The calculation is done in a linear colorspace, if the image gamma
1356is known.
1357
1358If you have a grayscale and you are using png_set_expand_depth(),
1359png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1360a higher bit-depth, you must either supply the background color as a gray
1361value at the original file bit-depth (need_expand = 1) or else supply the
1362background color as an RGB triplet at the final, expanded bit depth
1363(need_expand = 0). Similarly, if you are reading a paletted image, you
1364must either supply the background color as a palette index (need_expand = 1)
1365or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1366
1367 png_color_16 my_background;
1368 png_color_16p image_background;
1369
1370 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1371 png_set_background(png_ptr, image_background,
1372 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1373 else
1374 png_set_background(png_ptr, &my_background,
1375 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1376
1377The png_set_background() function tells libpng to composite images
1378with alpha or simple transparency against the supplied background
1379color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1380you may use this color, or supply another color more suitable for
1381the current display (e.g., the background color from a web page). You
1382need to tell libpng whether the color is in the gamma space of the
1383display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1384(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1385that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1386know why anyone would use this, but it's here).
1387
1388To properly display PNG images on any kind of system, the application needs
1389to know what the display gamma is. Ideally, the user will know this, and
1390the application will allow them to set it. One method of allowing the user
1391to set the display gamma separately for each system is to check for a
1392SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1393correctly set.
1394
1395Note that display_gamma is the overall gamma correction required to produce
1396pleasing results, which depends on the lighting conditions in the surrounding
1397environment. In a dim or brightly lit room, no compensation other than
1398the physical gamma exponent of the monitor is needed, while in a dark room
1399a slightly smaller exponent is better.
1400
1401 double gamma, screen_gamma;
1402
1403 if (/* We have a user-defined screen
1404 gamma value */)
1405 {
1406 screen_gamma = user_defined_screen_gamma;
1407 }
1408 /* One way that applications can share the same
1409 screen gamma value */
1410 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1411 != NULL)
1412 {
1413 screen_gamma = (double)atof(gamma_str);
1414 }
1415 /* If we don't have another value */
1416 else
1417 {
1418 screen_gamma = 2.2; /* A good guess for a
1419 PC monitor in a bright office or a dim room */
1420 screen_gamma = 2.0; /* A good guess for a
1421 PC monitor in a dark room */
1422 screen_gamma = 1.7 or 1.0; /* A good
1423 guess for Mac systems */
1424 }
1425
1426The png_set_gamma() function handles gamma transformations of the data.
1427Pass both the file gamma and the current screen_gamma. If the file does
1428not have a gamma value, you can pass one anyway if you have an idea what
1429it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1430that file gammas are inverted from screen gammas. See the discussions
1431on gamma in the PNG specification for an excellent description of what
1432gamma is, and why all applications should support it. It is strongly
1433recommended that PNG viewers support gamma correction.
1434
1435 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1436 png_set_gamma(png_ptr, screen_gamma, gamma);
1437 else
1438 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1439
1440If you need to reduce an RGB file to a paletted file, or if a paletted
1441file has more entries then will fit on your screen, png_set_dither()
1442will do that. Note that this is a simple match dither that merely
1443finds the closest color available. This should work fairly well with
1444optimized palettes, and fairly badly with linear color cubes. If you
1445pass a palette that is larger then maximum_colors, the file will
1446reduce the number of colors in the palette so it will fit into
1447maximum_colors. If there is a histogram, it will use it to make
1448more intelligent choices when reducing the palette. If there is no
1449histogram, it may not do as good a job.
1450
1451 if (color_type & PNG_COLOR_MASK_COLOR)
1452 {
1453 if (png_get_valid(png_ptr, info_ptr,
1454 PNG_INFO_PLTE))
1455 {
1456 png_uint_16p histogram = NULL;
1457
1458 png_get_hIST(png_ptr, info_ptr,
1459 &histogram);
1460 png_set_dither(png_ptr, palette, num_palette,
1461 max_screen_colors, histogram, 1);
1462 }
1463 else
1464 {
1465 png_color std_color_cube[MAX_SCREEN_COLORS] =
1466 { ... colors ... };
1467
1468 png_set_dither(png_ptr, std_color_cube,
1469 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1470 NULL,0);
1471 }
1472 }
1473
1474PNG files describe monochrome as black being zero and white being one.
1475The following code will reverse this (make black be one and white be
1476zero):
1477
1478 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1479 png_set_invert_mono(png_ptr);
1480
1481This function can also be used to invert grayscale and gray-alpha images:
1482
1483 if (color_type == PNG_COLOR_TYPE_GRAY ||
1484 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1485 png_set_invert_mono(png_ptr);
1486
1487PNG files store 16 bit pixels in network byte order (big-endian,
1488ie. most significant bits first). This code changes the storage to the
1489other way (little-endian, i.e. least significant bits first, the
1490way PCs store them):
1491
1492 if (bit_depth == 16)
1493 png_set_swap(png_ptr);
1494
1495If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1496need to change the order the pixels are packed into bytes, you can use:
1497
1498 if (bit_depth < 8)
1499 png_set_packswap(png_ptr);
1500
1501Finally, you can write your own transformation function if none of
1502the existing ones meets your needs. This is done by setting a callback
1503with
1504
1505 png_set_read_user_transform_fn(png_ptr,
1506 read_transform_fn);
1507
1508You must supply the function
1509
1510 void read_transform_fn(png_ptr ptr, row_info_ptr
1511 row_info, png_bytep data)
1512
1513See pngtest.c for a working example. Your function will be called
1514after all of the other transformations have been processed.
1515
1516You can also set up a pointer to a user structure for use by your
1517callback function, and you can inform libpng that your transform
1518function will change the number of channels or bit depth with the
1519function
1520
1521 png_set_user_transform_info(png_ptr, user_ptr,
1522 user_depth, user_channels);
1523
1524The user's application, not libpng, is responsible for allocating and
1525freeing any memory required for the user structure.
1526
1527You can retrieve the pointer via the function
1528png_get_user_transform_ptr(). For example:
1529
1530 voidp read_user_transform_ptr =
1531 png_get_user_transform_ptr(png_ptr);
1532
1533The last thing to handle is interlacing; this is covered in detail below,
1534but you must call the function here if you want libpng to handle expansion
1535of the interlaced image.
1536
1537 number_of_passes = png_set_interlace_handling(png_ptr);
1538
1539After setting the transformations, libpng can update your png_info
1540structure to reflect any transformations you've requested with this
1541call. This is most useful to update the info structure's rowbytes
1542field so you can use it to allocate your image memory. This function
1543will also update your palette with the correct screen_gamma and
1544background if these have been given with the calls above.
1545
1546 png_read_update_info(png_ptr, info_ptr);
1547
1548After you call png_read_update_info(), you can allocate any
1549memory you need to hold the image. The row data is simply
1550raw byte data for all forms of images. As the actual allocation
1551varies among applications, no example will be given. If you
1552are allocating one large chunk, you will need to build an
1553array of pointers to each row, as it will be needed for some
1554of the functions below.
1555
1556.SS Reading image data
1557
1558After you've allocated memory, you can read the image data.
1559The simplest way to do this is in one function call. If you are
1560allocating enough memory to hold the whole image, you can just
1561call png_read_image() and libpng will read in all the image data
1562and put it in the memory area supplied. You will need to pass in
1563an array of pointers to each row.
1564
1565This function automatically handles interlacing, so you don't need
1566to call png_set_interlace_handling() or call this function multiple
1567times, or any of that other stuff necessary with png_read_rows().
1568
1569 png_read_image(png_ptr, row_pointers);
1570
1571where row_pointers is:
1572
1573 png_bytep row_pointers[height];
1574
1575You can point to void or char or whatever you use for pixels.
1576
1577If you don't want to read in the whole image at once, you can
1578use png_read_rows() instead. If there is no interlacing (check
1579interlace_type == PNG_INTERLACE_NONE), this is simple:
1580
1581 png_read_rows(png_ptr, row_pointers, NULL,
1582 number_of_rows);
1583
1584where row_pointers is the same as in the png_read_image() call.
1585
1586If you are doing this just one row at a time, you can do this with
1587a single row_pointer instead of an array of row_pointers:
1588
1589 png_bytep row_pointer = row;
1590 png_read_row(png_ptr, row_pointer, NULL);
1591
1592If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1593get somewhat harder. The only current (PNG Specification version 1.2)
1594interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1595is a somewhat complicated 2D interlace scheme, known as Adam7, that
1596breaks down an image into seven smaller images of varying size, based
1597on an 8x8 grid.
1598
1599libpng can fill out those images or it can give them to you "as is".
1600If you want them filled out, there are two ways to do that. The one
1601mentioned in the PNG specification is to expand each pixel to cover
1602those pixels that have not been read yet (the "rectangle" method).
1603This results in a blocky image for the first pass, which gradually
1604smooths out as more pixels are read. The other method is the "sparkle"
1605method, where pixels are drawn only in their final locations, with the
1606rest of the image remaining whatever colors they were initialized to
1607before the start of the read. The first method usually looks better,
1608but tends to be slower, as there are more pixels to put in the rows.
1609
1610If you don't want libpng to handle the interlacing details, just call
1611png_read_rows() seven times to read in all seven images. Each of the
1612images is a valid image by itself, or they can all be combined on an
16138x8 grid to form a single image (although if you intend to combine them
1614you would be far better off using the libpng interlace handling).
1615
1616The first pass will return an image 1/8 as wide as the entire image
1617(every 8th column starting in column 0) and 1/8 as high as the original
1618(every 8th row starting in row 0), the second will be 1/8 as wide
1619(starting in column 4) and 1/8 as high (also starting in row 0). The
1620third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
16211/8 as high (every 8th row starting in row 4), and the fourth pass will
1622be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1623and every 4th row starting in row 0). The fifth pass will return an
1624image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1625while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1626(starting in column 1 and row 0). The seventh and final pass will be as
1627wide as the original, and 1/2 as high, containing all of the odd
1628numbered scanlines. Phew!
1629
1630If you want libpng to expand the images, call this before calling
1631png_start_read_image() or png_read_update_info():
1632
1633 if (interlace_type == PNG_INTERLACE_ADAM7)
1634 number_of_passes
1635 = png_set_interlace_handling(png_ptr);
1636
1637This will return the number of passes needed. Currently, this
1638is seven, but may change if another interlace type is added.
1639This function can be called even if the file is not interlaced,
1640where it will return one pass.
1641
1642If you are not going to display the image after each pass, but are
1643going to wait until the entire image is read in, use the sparkle
1644effect. This effect is faster and the end result of either method
1645is exactly the same. If you are planning on displaying the image
1646after each pass, the "rectangle" effect is generally considered the
1647better looking one.
1648
1649If you only want the "sparkle" effect, just call png_read_rows() as
1650normal, with the third parameter NULL. Make sure you make pass over
1651the image number_of_passes times, and you don't change the data in the
1652rows between calls. You can change the locations of the data, just
1653not the data. Each pass only writes the pixels appropriate for that
1654pass, and assumes the data from previous passes is still valid.
1655
1656 png_read_rows(png_ptr, row_pointers, NULL,
1657 number_of_rows);
1658
1659If you only want the first effect (the rectangles), do the same as
1660before except pass the row buffer in the third parameter, and leave
1661the second parameter NULL.
1662
1663 png_read_rows(png_ptr, NULL, row_pointers,
1664 number_of_rows);
1665
1666.SS Finishing a sequential read
1667
1668After you are finished reading the image through the
1669low-level interface, you can finish reading the file. If you are
1670interested in comments or time, which may be stored either before or
1671after the image data, you should pass the separate png_info struct if
1672you want to keep the comments from before and after the image
1673separate. If you are not interested, you can pass NULL.
1674
1675 png_read_end(png_ptr, end_info);
1676
1677When you are done, you can free all memory allocated by libpng like this:
1678
1679 png_destroy_read_struct(&png_ptr, &info_ptr,
1680 &end_info);
1681
1682It is also possible to individually free the info_ptr members that
1683point to libpng-allocated storage with the following function:
1684
1685 png_free_data(png_ptr, info_ptr, mask, seq)
1686 mask - identifies data to be freed, a mask
1687 containing the bitwise OR of one or
1688 more of
1689 PNG_FREE_PLTE, PNG_FREE_TRNS,
1690 PNG_FREE_HIST, PNG_FREE_ICCP,
1691 PNG_FREE_PCAL, PNG_FREE_ROWS,
1692 PNG_FREE_SCAL, PNG_FREE_SPLT,
1693 PNG_FREE_TEXT, PNG_FREE_UNKN,
1694 or simply PNG_FREE_ALL
1695 seq - sequence number of item to be freed
1696 (-1 for all items)
1697
1698This function may be safely called when the relevant storage has
1699already been freed, or has not yet been allocated, or was allocated
1700by the user and not by libpng, and will in those
1701cases do nothing. The "seq" parameter is ignored if only one item
1702of the selected data type, such as PLTE, is allowed. If "seq" is not
1703-1, and multiple items are allowed for the data type identified in
1704the mask, such as text or sPLT, only the n'th item in the structure
1705is freed, where n is "seq".
1706
1707The default behavior is only to free data that was allocated internally
1708by libpng. This can be changed, so that libpng will not free the data,
1709or so that it will free data that was allocated by the user with png_malloc()
1710or png_zalloc() and passed in via a png_set_*() function, with
1711
1712 png_data_freer(png_ptr, info_ptr, freer, mask)
1713 mask - which data elements are affected
1714 same choices as in png_free_data()
1715 freer - one of
1716 PNG_DESTROY_WILL_FREE_DATA
1717 PNG_SET_WILL_FREE_DATA
1718 PNG_USER_WILL_FREE_DATA
1719
1720This function only affects data that has already been allocated.
1721You can call this function after reading the PNG data but before calling
1722any png_set_*() functions, to control whether the user or the png_set_*()
1723function is responsible for freeing any existing data that might be present,
1724and again after the png_set_*() functions to control whether the user
1725or png_destroy_*() is supposed to free the data. When the user assumes
1726responsibility for libpng-allocated data, the application must use
1727png_free() to free it, and when the user transfers responsibility to libpng
1728for data that the user has allocated, the user must have used png_malloc()
1729or png_zalloc() to allocate it.
1730
1731If you allocated your row_pointers in a single block, as suggested above in
1732the description of the high level read interface, you must not transfer
1733responsibility for freeing it to the png_set_rows or png_read_destroy function,
1734because they would also try to free the individual row_pointers[i].
1735
1736If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
1737separately, do not transfer responsibility for freeing text_ptr to libpng,
1738because when libpng fills a png_text structure it combines these members with
1739the key member, and png_free_data() will free only text_ptr.key. Similarly,
1740if you transfer responsibility for free'ing text_ptr from libpng to your
1741application, your application must not separately free those members.
1742
1743The png_free_data() function will turn off the "valid" flag for anything
1744it frees. If you need to turn the flag off for a chunk that was freed by your
1745application instead of by libpng, you can use
1746
1747 png_set_invalid(png_ptr, info_ptr, mask);
1748 mask - identifies the chunks to be made invalid,
1749 containing the bitwise OR of one or
1750 more of
1751 PNG_INFO_gAMA, PNG_INFO_sBIT,
1752 PNG_INFO_cHRM, PNG_INFO_PLTE,
1753 PNG_INFO_tRNS, PNG_INFO_bKGD,
1754 PNG_INFO_hIST, PNG_INFO_pHYs,
1755 PNG_INFO_oFFs, PNG_INFO_tIME,
1756 PNG_INFO_pCAL, PNG_INFO_sRGB,
1757 PNG_INFO_iCCP, PNG_INFO_sPLT,
1758 PNG_INFO_sCAL, PNG_INFO_IDAT
1759
1760For a more compact example of reading a PNG image, see the file example.c.
1761
1762.SS Reading PNG files progressively
1763
1764The progressive reader is slightly different then the non-progressive
1765reader. Instead of calling png_read_info(), png_read_rows(), and
1766png_read_end(), you make one call to png_process_data(), which calls
1767callbacks when it has the info, a row, or the end of the image. You
1768set up these callbacks with png_set_progressive_read_fn(). You don't
1769have to worry about the input/output functions of libpng, as you are
1770giving the library the data directly in png_process_data(). I will
1771assume that you have read the section on reading PNG files above,
1772so I will only highlight the differences (although I will show
1773all of the code).
1774
1775png_structp png_ptr;
1776png_infop info_ptr;
1777
1778 /* An example code fragment of how you would
1779 initialize the progressive reader in your
1780 application. */
1781 int
1782 initialize_png_reader()
1783 {
1784 png_ptr = png_create_read_struct
1785 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1786 user_error_fn, user_warning_fn);
1787 if (!png_ptr)
1788 return (ERROR);
1789 info_ptr = png_create_info_struct(png_ptr);
1790 if (!info_ptr)
1791 {
1792 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
1793 (png_infopp)NULL);
1794 return (ERROR);
1795 }
1796
1797 if (setjmp(png_jmpbuf(png_ptr)))
1798 {
1799 png_destroy_read_struct(&png_ptr, &info_ptr,
1800 (png_infopp)NULL);
1801 return (ERROR);
1802 }
1803
1804 /* This one's new. You can provide functions
1805 to be called when the header info is valid,
1806 when each row is completed, and when the image
1807 is finished. If you aren't using all functions,
1808 you can specify NULL parameters. Even when all
1809 three functions are NULL, you need to call
1810 png_set_progressive_read_fn(). You can use
1811 any struct as the user_ptr (cast to a void pointer
1812 for the function call), and retrieve the pointer
1813 from inside the callbacks using the function
1814
1815 png_get_progressive_ptr(png_ptr);
1816
1817 which will return a void pointer, which you have
1818 to cast appropriately.
1819 */
1820 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
1821 info_callback, row_callback, end_callback);
1822
1823 return 0;
1824 }
1825
1826 /* A code fragment that you call as you receive blocks
1827 of data */
1828 int
1829 process_data(png_bytep buffer, png_uint_32 length)
1830 {
1831 if (setjmp(png_jmpbuf(png_ptr)))
1832 {
1833 png_destroy_read_struct(&png_ptr, &info_ptr,
1834 (png_infopp)NULL);
1835 return (ERROR);
1836 }
1837
1838 /* This one's new also. Simply give it a chunk
1839 of data from the file stream (in order, of
1840 course). On machines with segmented memory
1841 models machines, don't give it any more than
1842 64K. The library seems to run fine with sizes
1843 of 4K. Although you can give it much less if
1844 necessary (I assume you can give it chunks of
1845 1 byte, I haven't tried less then 256 bytes
1846 yet). When this function returns, you may
1847 want to display any rows that were generated
1848 in the row callback if you don't already do
1849 so there.
1850 */
1851 png_process_data(png_ptr, info_ptr, buffer, length);
1852 return 0;
1853 }
1854
1855 /* This function is called (as set by
1856 png_set_progressive_read_fn() above) when enough data
1857 has been supplied so all of the header has been
1858 read.
1859 */
1860 void
1861 info_callback(png_structp png_ptr, png_infop info)
1862 {
1863 /* Do any setup here, including setting any of
1864 the transformations mentioned in the Reading
1865 PNG files section. For now, you _must_ call
1866 either png_start_read_image() or
1867 png_read_update_info() after all the
1868 transformations are set (even if you don't set
1869 any). You may start getting rows before
1870 png_process_data() returns, so this is your
1871 last chance to prepare for that.
1872 */
1873 }
1874
1875 /* This function is called when each row of image
1876 data is complete */
1877 void
1878 row_callback(png_structp png_ptr, png_bytep new_row,
1879 png_uint_32 row_num, int pass)
1880 {
1881 /* If the image is interlaced, and you turned
1882 on the interlace handler, this function will
1883 be called for every row in every pass. Some
1884 of these rows will not be changed from the
1885 previous pass. When the row is not changed,
1886 the new_row variable will be NULL. The rows
1887 and passes are called in order, so you don't
1888 really need the row_num and pass, but I'm
1889 supplying them because it may make your life
1890 easier.
1891
1892 For the non-NULL rows of interlaced images,
1893 you must call png_progressive_combine_row()
1894 passing in the row and the old row. You can
1895 call this function for NULL rows (it will just
1896 return) and for non-interlaced images (it just
1897 does the memcpy for you) if it will make the
1898 code easier. Thus, you can just do this for
1899 all cases:
1900 */
1901
1902 png_progressive_combine_row(png_ptr, old_row,
1903 new_row);
1904
1905 /* where old_row is what was displayed for
1906 previously for the row. Note that the first
1907 pass (pass == 0, really) will completely cover
1908 the old row, so the rows do not have to be
1909 initialized. After the first pass (and only
1910 for interlaced images), you will have to pass
1911 the current row, and the function will combine
1912 the old row and the new row.
1913 */
1914 }
1915
1916 void
1917 end_callback(png_structp png_ptr, png_infop info)
1918 {
1919 /* This function is called after the whole image
1920 has been read, including any chunks after the
1921 image (up to and including the IEND). You
1922 will usually have the same info chunk as you
1923 had in the header, although some data may have
1924 been added to the comments and time fields.
1925
1926 Most people won't do much here, perhaps setting
1927 a flag that marks the image as finished.
1928 */
1929 }
1930
1931
1932
1933.SH IV. Writing
1934
1935Much of this is very similar to reading. However, everything of
1936importance is repeated here, so you won't have to constantly look
1937back up in the reading section to understand writing.
1938
1939.SS Setup
1940
1941You will want to do the I/O initialization before you get into libpng,
1942so if it doesn't work, you don't have anything to undo. If you are not
1943using the standard I/O functions, you will need to replace them with
1944custom writing functions. See the discussion under Customizing libpng.
1945
1946 FILE *fp = fopen(file_name, "wb");
1947 if (!fp)
1948 {
1949 return (ERROR);
1950 }
1951
1952Next, png_struct and png_info need to be allocated and initialized.
1953As these can be both relatively large, you may not want to store these
1954on the stack, unless you have stack space to spare. Of course, you
1955will want to check if they return NULL. If you are also reading,
1956you won't want to name your read structure and your write structure
1957both "png_ptr"; you can call them anything you like, such as
1958"read_ptr" and "write_ptr". Look at pngtest.c, for example.
1959
1960 png_structp png_ptr = png_create_write_struct
1961 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1962 user_error_fn, user_warning_fn);
1963 if (!png_ptr)
1964 return (ERROR);
1965
1966 png_infop info_ptr = png_create_info_struct(png_ptr);
1967 if (!info_ptr)
1968 {
1969 png_destroy_write_struct(&png_ptr,
1970 (png_infopp)NULL);
1971 return (ERROR);
1972 }
1973
1974If you want to use your own memory allocation routines,
1975define PNG_USER_MEM_SUPPORTED and use
1976png_create_write_struct_2() instead of png_create_write_struct():
1977
1978 png_structp png_ptr = png_create_write_struct_2
1979 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1980 user_error_fn, user_warning_fn, (png_voidp)
1981 user_mem_ptr, user_malloc_fn, user_free_fn);
1982
1983After you have these structures, you will need to set up the
1984error handling. When libpng encounters an error, it expects to
1985longjmp() back to your routine. Therefore, you will need to call
1986setjmp() and pass the png_jmpbuf(png_ptr). If you
1987write the file from different routines, you will need to update
1988the png_jmpbuf(png_ptr) every time you enter a new routine that will
1989call a png_*() function. See your documentation of setjmp/longjmp
1990for your compiler for more information on setjmp/longjmp. See
1991the discussion on libpng error handling in the Customizing Libpng
1992section below for more information on the libpng error handling.
1993
1994 if (setjmp(png_jmpbuf(png_ptr)))
1995 {
1996 png_destroy_write_struct(&png_ptr, &info_ptr);
1997 fclose(fp);
1998 return (ERROR);
1999 }
2000 ...
2001 return;
2002
2003If you would rather avoid the complexity of setjmp/longjmp issues,
2004you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2005errors will result in a call to PNG_ABORT() which defaults to abort().
2006
2007Now you need to set up the output code. The default for libpng is to
2008use the C function fwrite(). If you use this, you will need to pass a
2009valid FILE * in the function png_init_io(). Be sure that the file is
2010opened in binary mode. Again, if you wish to handle writing data in
2011another way, see the discussion on libpng I/O handling in the Customizing
2012Libpng section below.
2013
2014 png_init_io(png_ptr, fp);
2015
2016If you are embedding your PNG into a datastream such as MNG, and don't
2017want libpng to write the 8-byte signature, or if you have already
2018written the signature in your application, use
2019
2020 png_set_sig_bytes(png_ptr, 8);
2021
2022to inform libpng that it should not write a signature.
2023
2024.SS Write callbacks
2025
2026At this point, you can set up a callback function that will be
2027called after each row has been written, which you can use to control
2028a progress meter or the like. It's demonstrated in pngtest.c.
2029You must supply a function
2030
2031 void write_row_callback(png_ptr, png_uint_32 row,
2032 int pass);
2033 {
2034 /* put your code here */
2035 }
2036
2037(You can give it another name that you like instead of "write_row_callback")
2038
2039To inform libpng about your function, use
2040
2041 png_set_write_status_fn(png_ptr, write_row_callback);
2042
2043You now have the option of modifying how the compression library will
2044run. The following functions are mainly for testing, but may be useful
2045in some cases, like if you need to write PNG files extremely fast and
2046are willing to give up some compression, or if you want to get the
2047maximum possible compression at the expense of slower writing. If you
2048have no special needs in this area, let the library do what it wants by
2049not calling this function at all, as it has been tuned to deliver a good
2050speed/compression ratio. The second parameter to png_set_filter() is
2051the filter method, for which the only valid values are 0 (as of the
2052July 1999 PNG specification, version 1.2) or 64 (if you are writing
2053a PNG datastream that is to be embedded in a MNG datastream). The third
2054parameter is a flag that indicates which filter type(s) are to be tested
2055for each scanline. See the PNG specification for details on the specific filter
2056types.
2057
2058
2059 /* turn on or off filtering, and/or choose
2060 specific filters. You can use either a single
2061 PNG_FILTER_VALUE_NAME or the bitwise OR of one
2062 or more PNG_FILTER_NAME masks. */
2063 png_set_filter(png_ptr, 0,
2064 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2065 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2066 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2067 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2068 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2069 PNG_ALL_FILTERS);
2070
2071If an application
2072wants to start and stop using particular filters during compression,
2073it should start out with all of the filters (to ensure that the previous
2074row of pixels will be stored in case it's needed later), and then add
2075and remove them after the start of compression.
2076
2077If you are writing a PNG datastream that is to be embedded in a MNG
2078datastream, the second parameter can be either 0 or 64.
2079
2080The png_set_compression_*() functions interface to the zlib compression
2081library, and should mostly be ignored unless you really know what you are
2082doing. The only generally useful call is png_set_compression_level()
2083which changes how much time zlib spends on trying to compress the image
2084data. See the Compression Library (zlib.h and algorithm.txt, distributed
2085with zlib) for details on the compression levels.
2086
2087 /* set the zlib compression level */
2088 png_set_compression_level(png_ptr,
2089 Z_BEST_COMPRESSION);
2090
2091 /* set other zlib parameters */
2092 png_set_compression_mem_level(png_ptr, 8);
2093 png_set_compression_strategy(png_ptr,
2094 Z_DEFAULT_STRATEGY);
2095 png_set_compression_window_bits(png_ptr, 15);
2096 png_set_compression_method(png_ptr, 8);
2097 png_set_compression_buffer_size(png_ptr, 8192)
2098
2099extern PNG_EXPORT(void,png_set_zbuf_size)
2100
2101.SS Setting the contents of info for output
2102
2103You now need to fill in the png_info structure with all the data you
2104wish to write before the actual image. Note that the only thing you
2105are allowed to write after the image is the text chunks and the time
2106chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2107the latest PNG specification for more information on that. If you
2108wish to write them before the image, fill them in now, and flag that
2109data as being valid. If you want to wait until after the data, don't
2110fill them until png_write_end(). For all the fields in png_info and
2111their data types, see png.h. For explanations of what the fields
2112contain, see the PNG specification.
2113
2114Some of the more important parts of the png_info are:
2115
2116 png_set_IHDR(png_ptr, info_ptr, width, height,
2117 bit_depth, color_type, interlace_type,
2118 compression_type, filter_method)
2119 width - holds the width of the image
2120 in pixels (up to 2^31).
2121 height - holds the height of the image
2122 in pixels (up to 2^31).
2123 bit_depth - holds the bit depth of one of the
2124 image channels.
2125 (valid values are 1, 2, 4, 8, 16
2126 and depend also on the
2127 color_type. See also significant
2128 bits (sBIT) below).
2129 color_type - describes which color/alpha
2130 channels are present.
2131 PNG_COLOR_TYPE_GRAY
2132 (bit depths 1, 2, 4, 8, 16)
2133 PNG_COLOR_TYPE_GRAY_ALPHA
2134 (bit depths 8, 16)
2135 PNG_COLOR_TYPE_PALETTE
2136 (bit depths 1, 2, 4, 8)
2137 PNG_COLOR_TYPE_RGB
2138 (bit_depths 8, 16)
2139 PNG_COLOR_TYPE_RGB_ALPHA
2140 (bit_depths 8, 16)
2141
2142 PNG_COLOR_MASK_PALETTE
2143 PNG_COLOR_MASK_COLOR
2144 PNG_COLOR_MASK_ALPHA
2145
2146 interlace_type - PNG_INTERLACE_NONE or
2147 PNG_INTERLACE_ADAM7
2148 compression_type - (must be
2149 PNG_COMPRESSION_TYPE_DEFAULT)
2150 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2151 or, if you are writing a PNG to
2152 be embedded in a MNG datastream,
2153 can also be
2154 PNG_INTRAPIXEL_DIFFERENCING)
2155
2156 png_set_PLTE(png_ptr, info_ptr, palette,
2157 num_palette);
2158 palette - the palette for the file
2159 (array of png_color)
2160 num_palette - number of entries in the palette
2161
2162 png_set_gAMA(png_ptr, info_ptr, gamma);
2163 gamma - the gamma the image was created
2164 at (PNG_INFO_gAMA)
2165
2166 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2167 srgb_intent - the rendering intent
2168 (PNG_INFO_sRGB) The presence of
2169 the sRGB chunk means that the pixel
2170 data is in the sRGB color space.
2171 This chunk also implies specific
2172 values of gAMA and cHRM. Rendering
2173 intent is the CSS-1 property that
2174 has been defined by the International
2175 Color Consortium
2176 (http://www.color.org).
2177 It can be one of
2178 PNG_sRGB_INTENT_SATURATION,
2179 PNG_sRGB_INTENT_PERCEPTUAL,
2180 PNG_sRGB_INTENT_ABSOLUTE, or
2181 PNG_sRGB_INTENT_RELATIVE.
2182
2183
2184 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2185 srgb_intent);
2186 srgb_intent - the rendering intent
2187 (PNG_INFO_sRGB) The presence of the
2188 sRGB chunk means that the pixel
2189 data is in the sRGB color space.
2190 This function also causes gAMA and
2191 cHRM chunks with the specific values
2192 that are consistent with sRGB to be
2193 written.
2194
2195 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2196 profile, proflen);
2197 name - The profile name.
2198 compression - The compression type; always
2199 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2200 You may give NULL to this argument to
2201 ignore it.
2202 profile - International Color Consortium color
2203 profile data. May contain NULs.
2204 proflen - length of profile data in bytes.
2205
2206 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2207 sig_bit - the number of significant bits for
2208 (PNG_INFO_sBIT) each of the gray, red,
2209 green, and blue channels, whichever are
2210 appropriate for the given color type
2211 (png_color_16)
2212
2213 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2214 trans_values);
2215 trans - array of transparent entries for
2216 palette (PNG_INFO_tRNS)
2217 trans_values - graylevel or color sample values of
2218 the single transparent color for
2219 non-paletted images (PNG_INFO_tRNS)
2220 num_trans - number of transparent entries
2221 (PNG_INFO_tRNS)
2222
2223 png_set_hIST(png_ptr, info_ptr, hist);
2224 (PNG_INFO_hIST)
2225 hist - histogram of palette (array of
2226 png_uint_16)
2227
2228 png_set_tIME(png_ptr, info_ptr, mod_time);
2229 mod_time - time image was last modified
2230 (PNG_VALID_tIME)
2231
2232 png_set_bKGD(png_ptr, info_ptr, background);
2233 background - background color (PNG_VALID_bKGD)
2234
2235 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2236 text_ptr - array of png_text holding image
2237 comments
2238 text_ptr[i].compression - type of compression used
2239 on "text" PNG_TEXT_COMPRESSION_NONE
2240 PNG_TEXT_COMPRESSION_zTXt
2241 PNG_ITXT_COMPRESSION_NONE
2242 PNG_ITXT_COMPRESSION_zTXt
2243 text_ptr[i].key - keyword for comment. Must contain
2244 1-79 characters.
2245 text_ptr[i].text - text comments for current
2246 keyword. Can be NULL or empty.
2247 text_ptr[i].text_length - length of text string,
2248 after decompression, 0 for iTXt
2249 text_ptr[i].itxt_length - length of itxt string,
2250 after decompression, 0 for tEXt/zTXt
2251 text_ptr[i].lang - language of comment (NULL or
2252 empty for unknown).
2253 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2254 or empty for unknown).
2255 num_text - number of comments
2256
2257 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2258 num_spalettes);
2259 palette_ptr - array of png_sPLT_struct structures
2260 to be added to the list of palettes
2261 in the info structure.
2262 num_spalettes - number of palette structures to be
2263 added.
2264
2265 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2266 unit_type);
2267 offset_x - positive offset from the left
2268 edge of the screen
2269 offset_y - positive offset from the top
2270 edge of the screen
2271 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2272
2273 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2274 unit_type);
2275 res_x - pixels/unit physical resolution
2276 in x direction
2277 res_y - pixels/unit physical resolution
2278 in y direction
2279 unit_type - PNG_RESOLUTION_UNKNOWN,
2280 PNG_RESOLUTION_METER
2281
2282 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2283 unit - physical scale units (an integer)
2284 width - width of a pixel in physical scale units
2285 height - height of a pixel in physical scale units
2286 (width and height are doubles)
2287
2288 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2289 unit - physical scale units (an integer)
2290 width - width of a pixel in physical scale units
2291 height - height of a pixel in physical scale units
2292 (width and height are strings like "2.54")
2293
2294 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2295 num_unknowns)
2296 unknowns - array of png_unknown_chunk
2297 structures holding unknown chunks
2298 unknowns[i].name - name of unknown chunk
2299 unknowns[i].data - data of unknown chunk
2300 unknowns[i].size - size of unknown chunk's data
2301 unknowns[i].location - position to write chunk in file
2302 0: do not write chunk
2303 PNG_HAVE_IHDR: before PLTE
2304 PNG_HAVE_PLTE: before IDAT
2305 PNG_AFTER_IDAT: after IDAT
2306
2307The "location" member is set automatically according to
2308what part of the output file has already been written.
2309You can change its value after calling png_set_unknown_chunks()
2310as demonstrated in pngtest.c. Within each of the "locations",
2311the chunks are sequenced according to their position in the
2312structure (that is, the value of "i", which is the order in which
2313the chunk was either read from the input file or defined with
2314png_set_unknown_chunks).
2315
2316A quick word about text and num_text. text is an array of png_text
2317structures. num_text is the number of valid structures in the array.
2318Each png_text structure holds a language code, a keyword, a text value,
2319and a compression type.
2320
2321The compression types have the same valid numbers as the compression
2322types of the image data. Currently, the only valid number is zero.
2323However, you can store text either compressed or uncompressed, unlike
2324images, which always have to be compressed. So if you don't want the
2325text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2326Because tEXt and zTXt chunks don't have a language field, if you
2327specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2328any language code or translated keyword will not be written out.
2329
2330Until text gets around 1000 bytes, it is not worth compressing it.
2331After the text has been written out to the file, the compression type
2332is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2333so that it isn't written out again at the end (in case you are calling
2334png_write_end() with the same struct.
2335
2336The keywords that are given in the PNG Specification are:
2337
2338 Title Short (one line) title or
2339 caption for image
2340 Author Name of image's creator
2341 Description Description of image (possibly long)
2342 Copyright Copyright notice
2343 Creation Time Time of original image creation
2344 (usually RFC 1123 format, see below)
2345 Software Software used to create the image
2346 Disclaimer Legal disclaimer
2347 Warning Warning of nature of content
2348 Source Device used to create the image
2349 Comment Miscellaneous comment; conversion
2350 from other image format
2351
2352The keyword-text pairs work like this. Keywords should be short
2353simple descriptions of what the comment is about. Some typical
2354keywords are found in the PNG specification, as is some recommendations
2355on keywords. You can repeat keywords in a file. You can even write
2356some text before the image and some after. For example, you may want
2357to put a description of the image before the image, but leave the
2358disclaimer until after, so viewers working over modem connections
2359don't have to wait for the disclaimer to go over the modem before
2360they start seeing the image. Finally, keywords should be full
2361words, not abbreviations. Keywords and text are in the ISO 8859-1
2362(Latin-1) character set (a superset of regular ASCII) and can not
2363contain NUL characters, and should not contain control or other
2364unprintable characters. To make the comments widely readable, stick
2365with basic ASCII, and avoid machine specific character set extensions
2366like the IBM-PC character set. The keyword must be present, but
2367you can leave off the text string on non-compressed pairs.
2368Compressed pairs must have a text string, as only the text string
2369is compressed anyway, so the compression would be meaningless.
2370
2371PNG supports modification time via the png_time structure. Two
2372conversion routines are provided, png_convert_from_time_t() for
2373time_t and png_convert_from_struct_tm() for struct tm. The
2374time_t routine uses gmtime(). You don't have to use either of
2375these, but if you wish to fill in the png_time structure directly,
2376you should provide the time in universal time (GMT) if possible
2377instead of your local time. Note that the year number is the full
2378year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2379that months start with 1.
2380
2381If you want to store the time of the original image creation, you should
2382use a plain tEXt chunk with the "Creation Time" keyword. This is
2383necessary because the "creation time" of a PNG image is somewhat vague,
2384depending on whether you mean the PNG file, the time the image was
2385created in a non-PNG format, a still photo from which the image was
2386scanned, or possibly the subject matter itself. In order to facilitate
2387machine-readable dates, it is recommended that the "Creation Time"
2388tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2389although this isn't a requirement. Unlike the tIME chunk, the
2390"Creation Time" tEXt chunk is not expected to be automatically changed
2391by the software. To facilitate the use of RFC 1123 dates, a function
2392png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2393time to an RFC 1123 format string.
2394
2395.SS Writing unknown chunks
2396
2397You can use the png_set_unknown_chunks function to queue up chunks
2398for writing. You give it a chunk name, raw data, and a size; that's
2399all there is to it. The chunks will be written by the next following
2400png_write_info_before_PLTE, png_write_info, or png_write_end function.
2401Any chunks previously read into the info structure's unknown-chunk
2402list will also be written out in a sequence that satisfies the PNG
2403specification's ordering rules.
2404
2405.SS The high-level write interface
2406
2407At this point there are two ways to proceed; through the high-level
2408write interface, or through a sequence of low-level write operations.
2409You can use the high-level interface if your image data is present
2410in the info structure. All defined output
2411transformations are permitted, enabled by the following masks.
2412
2413 PNG_TRANSFORM_IDENTITY No transformation
2414 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2415 PNG_TRANSFORM_PACKSWAP Change order of packed
2416 pixels to LSB first
2417 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2418 PNG_TRANSFORM_SHIFT Normalize pixels to the
2419 sBIT depth
2420 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2421 to BGRA
2422 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2423 to AG
2424 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2425 to transparency
2426 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2427 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2428
2429If you have valid image data in the info structure (you can use
2430png_set_rows() to put image data in the info structure), simply do this:
2431
2432 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2433
2434where png_transforms is an integer containing the bitwise OR of some set of
2435transformation flags. This call is equivalent to png_write_info(),
2436followed the set of transformations indicated by the transform mask,
2437then png_write_image(), and finally png_write_end().
2438
2439(The final parameter of this call is not yet used. Someday it might point
2440to transformation parameters required by some future output transform.)
2441
2442You must use png_transforms and not call any png_set_transform() functions
2443when you use png_write_png().
2444
2445.SS The low-level write interface
2446
2447If you are going the low-level route instead, you are now ready to
2448write all the file information up to the actual image data. You do
2449this with a call to png_write_info().
2450
2451 png_write_info(png_ptr, info_ptr);
2452
2453Note that there is one transformation you may need to do before
2454png_write_info(). In PNG files, the alpha channel in an image is the
2455level of opacity. If your data is supplied as a level of
2456transparency, you can invert the alpha channel before you write it, so
2457that 0 is fully transparent and 255 (in 8-bit or paletted images) or
245865535 (in 16-bit images) is fully opaque, with
2459
2460 png_set_invert_alpha(png_ptr);
2461
2462This must appear before png_write_info() instead of later with the
2463other transformations because in the case of paletted images the tRNS
2464chunk data has to be inverted before the tRNS chunk is written. If
2465your image is not a paletted image, the tRNS data (which in such cases
2466represents a single color to be rendered as transparent) won't need to
2467be changed, and you can safely do this transformation after your
2468png_write_info() call.
2469
2470If you need to write a private chunk that you want to appear before
2471the PLTE chunk when PLTE is present, you can write the PNG info in
2472two steps, and insert code to write your own chunk between them:
2473
2474 png_write_info_before_PLTE(png_ptr, info_ptr);
2475 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2476 png_write_info(png_ptr, info_ptr);
2477
2478After you've written the file information, you can set up the library
2479to handle any special transformations of the image data. The various
2480ways to transform the data will be described in the order that they
2481should occur. This is important, as some of these change the color
2482type and/or bit depth of the data, and some others only work on
2483certain color types and bit depths. Even though each transformation
2484checks to see if it has data that it can do something with, you should
2485make sure to only enable a transformation if it will be valid for the
2486data. For example, don't swap red and blue on grayscale data.
2487
2488PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2489the library to strip input data that has 4 or 8 bytes per pixel down
2490to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2491bytes per pixel).
2492
2493 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2494
2495where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2496PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2497is stored XRGB or RGBX.
2498
2499PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2500they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2501If the data is supplied at 1 pixel per byte, use this code, which will
2502correctly pack the pixels into a single byte:
2503
2504 png_set_packing(png_ptr);
2505
2506PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2507data is of another bit depth, you can write an sBIT chunk into the
2508file so that decoders can recover the original data if desired.
2509
2510 /* Set the true bit depth of the image data */
2511 if (color_type & PNG_COLOR_MASK_COLOR)
2512 {
2513 sig_bit.red = true_bit_depth;
2514 sig_bit.green = true_bit_depth;
2515 sig_bit.blue = true_bit_depth;
2516 }
2517 else
2518 {
2519 sig_bit.gray = true_bit_depth;
2520 }
2521 if (color_type & PNG_COLOR_MASK_ALPHA)
2522 {
2523 sig_bit.alpha = true_bit_depth;
2524 }
2525
2526 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2527
2528If the data is stored in the row buffer in a bit depth other than
2529one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2530this will scale the values to appear to be the correct bit depth as
2531is required by PNG.
2532
2533 png_set_shift(png_ptr, &sig_bit);
2534
2535PNG files store 16 bit pixels in network byte order (big-endian,
2536ie. most significant bits first). This code would be used if they are
2537supplied the other way (little-endian, i.e. least significant bits
2538first, the way PCs store them):
2539
2540 if (bit_depth > 8)
2541 png_set_swap(png_ptr);
2542
2543If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2544need to change the order the pixels are packed into bytes, you can use:
2545
2546 if (bit_depth < 8)
2547 png_set_packswap(png_ptr);
2548
2549PNG files store 3 color pixels in red, green, blue order. This code
2550would be used if they are supplied as blue, green, red:
2551
2552 png_set_bgr(png_ptr);
2553
2554PNG files describe monochrome as black being zero and white being
2555one. This code would be used if the pixels are supplied with this reversed
2556(black being one and white being zero):
2557
2558 png_set_invert_mono(png_ptr);
2559
2560Finally, you can write your own transformation function if none of
2561the existing ones meets your needs. This is done by setting a callback
2562with
2563
2564 png_set_write_user_transform_fn(png_ptr,
2565 write_transform_fn);
2566
2567You must supply the function
2568
2569 void write_transform_fn(png_ptr ptr, row_info_ptr
2570 row_info, png_bytep data)
2571
2572See pngtest.c for a working example. Your function will be called
2573before any of the other transformations are processed.
2574
2575You can also set up a pointer to a user structure for use by your
2576callback function.
2577
2578 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2579
2580The user_channels and user_depth parameters of this function are ignored
2581when writing; you can set them to zero as shown.
2582
2583You can retrieve the pointer via the function png_get_user_transform_ptr().
2584For example:
2585
2586 voidp write_user_transform_ptr =
2587 png_get_user_transform_ptr(png_ptr);
2588
2589It is possible to have libpng flush any pending output, either manually,
2590or automatically after a certain number of lines have been written. To
2591flush the output stream a single time call:
2592
2593 png_write_flush(png_ptr);
2594
2595and to have libpng flush the output stream periodically after a certain
2596number of scanlines have been written, call:
2597
2598 png_set_flush(png_ptr, nrows);
2599
2600Note that the distance between rows is from the last time png_write_flush()
2601was called, or the first row of the image if it has never been called.
2602So if you write 50 lines, and then png_set_flush 25, it will flush the
2603output on the next scanline, and every 25 lines thereafter, unless
2604png_write_flush() is called before 25 more lines have been written.
2605If nrows is too small (less than about 10 lines for a 640 pixel wide
2606RGB image) the image compression may decrease noticeably (although this
2607may be acceptable for real-time applications). Infrequent flushing will
2608only degrade the compression performance by a few percent over images
2609that do not use flushing.
2610
2611.SS Writing the image data
2612
2613That's it for the transformations. Now you can write the image data.
2614The simplest way to do this is in one function call. If you have the
2615whole image in memory, you can just call png_write_image() and libpng
2616will write the image. You will need to pass in an array of pointers to
2617each row. This function automatically handles interlacing, so you don't
2618need to call png_set_interlace_handling() or call this function multiple
2619times, or any of that other stuff necessary with png_write_rows().
2620
2621 png_write_image(png_ptr, row_pointers);
2622
2623where row_pointers is:
2624
2625 png_byte *row_pointers[height];
2626
2627You can point to void or char or whatever you use for pixels.
2628
2629If you don't want to write the whole image at once, you can
2630use png_write_rows() instead. If the file is not interlaced,
2631this is simple:
2632
2633 png_write_rows(png_ptr, row_pointers,
2634 number_of_rows);
2635
2636row_pointers is the same as in the png_write_image() call.
2637
2638If you are just writing one row at a time, you can do this with
2639a single row_pointer instead of an array of row_pointers:
2640
2641 png_bytep row_pointer = row;
2642
2643 png_write_row(png_ptr, row_pointer);
2644
2645When the file is interlaced, things can get a good deal more
2646complicated. The only currently (as of the PNG Specification
2647version 1.2, dated July 1999) defined interlacing scheme for PNG files
2648is the "Adam7" interlace scheme, that breaks down an
2649image into seven smaller images of varying size. libpng will build
2650these images for you, or you can do them yourself. If you want to
2651build them yourself, see the PNG specification for details of which
2652pixels to write when.
2653
2654If you don't want libpng to handle the interlacing details, just
2655use png_set_interlace_handling() and call png_write_rows() the
2656correct number of times to write all seven sub-images.
2657
2658If you want libpng to build the sub-images, call this before you start
2659writing any rows:
2660
2661 number_of_passes =
2662 png_set_interlace_handling(png_ptr);
2663
2664This will return the number of passes needed. Currently, this
2665is seven, but may change if another interlace type is added.
2666
2667Then write the complete image number_of_passes times.
2668
2669 png_write_rows(png_ptr, row_pointers,
2670 number_of_rows);
2671
2672As some of these rows are not used, and thus return immediately,
2673you may want to read about interlacing in the PNG specification,
2674and only update the rows that are actually used.
2675
2676.SS Finishing a sequential write
2677
2678After you are finished writing the image, you should finish writing
2679the file. If you are interested in writing comments or time, you should
2680pass an appropriately filled png_info pointer. If you are not interested,
2681you can pass NULL.
2682
2683 png_write_end(png_ptr, info_ptr);
2684
2685When you are done, you can free all memory used by libpng like this:
2686
2687 png_destroy_write_struct(&png_ptr, &info_ptr);
2688
2689It is also possible to individually free the info_ptr members that
2690point to libpng-allocated storage with the following function:
2691
2692 png_free_data(png_ptr, info_ptr, mask, seq)
2693 mask - identifies data to be freed, a mask
2694 containing the bitwise OR of one or
2695 more of
2696 PNG_FREE_PLTE, PNG_FREE_TRNS,
2697 PNG_FREE_HIST, PNG_FREE_ICCP,
2698 PNG_FREE_PCAL, PNG_FREE_ROWS,
2699 PNG_FREE_SCAL, PNG_FREE_SPLT,
2700 PNG_FREE_TEXT, PNG_FREE_UNKN,
2701 or simply PNG_FREE_ALL
2702 seq - sequence number of item to be freed
2703 (-1 for all items)
2704
2705This function may be safely called when the relevant storage has
2706already been freed, or has not yet been allocated, or was allocated
2707by the user and not by libpng, and will in those
2708cases do nothing. The "seq" parameter is ignored if only one item
2709of the selected data type, such as PLTE, is allowed. If "seq" is not
2710-1, and multiple items are allowed for the data type identified in
2711the mask, such as text or sPLT, only the n'th item in the structure
2712is freed, where n is "seq".
2713
2714If you allocated data such as a palette that you passed
2715in to libpng with png_set_*, you must not free it until just before the call to
2716png_destroy_write_struct().
2717
2718The default behavior is only to free data that was allocated internally
2719by libpng. This can be changed, so that libpng will not free the data,
2720or so that it will free data that was allocated by the user with png_malloc()
2721or png_zalloc() and passed in via a png_set_*() function, with
2722
2723 png_data_freer(png_ptr, info_ptr, freer, mask)
2724 mask - which data elements are affected
2725 same choices as in png_free_data()
2726 freer - one of
2727 PNG_DESTROY_WILL_FREE_DATA
2728 PNG_SET_WILL_FREE_DATA
2729 PNG_USER_WILL_FREE_DATA
2730
2731For example, to transfer responsibility for some data from a read structure
2732to a write structure, you could use
2733
2734 png_data_freer(read_ptr, read_info_ptr,
2735 PNG_USER_WILL_FREE_DATA,
2736 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
2737 png_data_freer(write_ptr, write_info_ptr,
2738 PNG_DESTROY_WILL_FREE_DATA,
2739 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
2740
2741thereby briefly reassigning responsibility for freeing to the user but
2742immediately afterwards reassigning it once more to the write_destroy
2743function. Having done this, it would then be safe to destroy the read
2744structure and continue to use the PLTE, tRNS, and hIST data in the write
2745structure.
2746
2747This function only affects data that has already been allocated.
2748You can call this function before calling after the png_set_*() functions
2749to control whether the user or png_destroy_*() is supposed to free the data.
2750When the user assumes responsibility for libpng-allocated data, the
2751application must use
2752png_free() to free it, and when the user transfers responsibility to libpng
2753for data that the user has allocated, the user must have used png_malloc()
2754or png_zalloc() to allocate it.
2755
2756If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2757separately, do not transfer responsibility for freeing text_ptr to libpng,
2758because when libpng fills a png_text structure it combines these members with
2759the key member, and png_free_data() will free only text_ptr.key. Similarly,
2760if you transfer responsibility for free'ing text_ptr from libpng to your
2761application, your application must not separately free those members.
2762For a more compact example of writing a PNG image, see the file example.c.
2763
2764.SH V. Modifying/Customizing libpng:
2765
2766There are two issues here. The first is changing how libpng does
2767standard things like memory allocation, input/output, and error handling.
2768The second deals with more complicated things like adding new chunks,
2769adding new transformations, and generally changing how libpng works.
2770Both of those are compile-time issues; that is, they are generally
2771determined at the time the code is written, and there is rarely a need
2772to provide the user with a means of changing them.
2773
2774Memory allocation, input/output, and error handling
2775
2776All of the memory allocation, input/output, and error handling in libpng
2777goes through callbacks that are user-settable. The default routines are
2778in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
2779these functions, call the appropriate png_set_*_fn() function.
2780
2781Memory allocation is done through the functions png_malloc()
2782and png_free(). These currently just call the standard C functions. If
2783your pointers can't access more then 64K at a time, you will want to set
2784MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
2785memory allocation on a platform will change between applications, these
2786functions must be modified in the library at compile time. If you prefer
2787to use a different method of allocating and freeing data, you can use
2788png_create_read_struct_2() or png_create_write_struct_2() to register
2789your own functions as described above.
2790These functions also provide a void pointer that can be retrieved via
2791
2792 mem_ptr=png_get_mem_ptr(png_ptr);
2793
2794Your replacement memory functions must have prototypes as follows:
2795
2796 png_voidp malloc_fn(png_structp png_ptr,
2797 png_size_t size);
2798 void free_fn(png_structp png_ptr, png_voidp ptr);
2799
2800Your malloc_fn() must return NULL in case of failure. The png_malloc()
2801function will normally call png_error() if it receives a NULL from the
2802system memory allocator or from your replacement malloc_fn().
2803
2804Input/Output in libpng is done through png_read() and png_write(),
2805which currently just call fread() and fwrite(). The FILE * is stored in
2806png_struct and is initialized via png_init_io(). If you wish to change
2807the method of I/O, the library supplies callbacks that you can set
2808through the function png_set_read_fn() and png_set_write_fn() at run
2809time, instead of calling the png_init_io() function. These functions
2810also provide a void pointer that can be retrieved via the function
2811png_get_io_ptr(). For example:
2812
2813 png_set_read_fn(png_structp read_ptr,
2814 voidp read_io_ptr, png_rw_ptr read_data_fn)
2815
2816 png_set_write_fn(png_structp write_ptr,
2817 voidp write_io_ptr, png_rw_ptr write_data_fn,
2818 png_flush_ptr output_flush_fn);
2819
2820 voidp read_io_ptr = png_get_io_ptr(read_ptr);
2821 voidp write_io_ptr = png_get_io_ptr(write_ptr);
2822
2823The replacement I/O functions must have prototypes as follows:
2824
2825 void user_read_data(png_structp png_ptr,
2826 png_bytep data, png_size_t length);
2827 void user_write_data(png_structp png_ptr,
2828 png_bytep data, png_size_t length);
2829 void user_flush_data(png_structp png_ptr);
2830
2831Supplying NULL for the read, write, or flush functions sets them back
2832to using the default C stream functions. It is an error to read from
2833a write stream, and vice versa.
2834
2835Error handling in libpng is done through png_error() and png_warning().
2836Errors handled through png_error() are fatal, meaning that png_error()
2837should never return to its caller. Currently, this is handled via
2838setjmp() and longjmp() (unless you have compiled libpng with
2839PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
2840but you could change this to do things like exit() if you should wish.
2841
2842On non-fatal errors, png_warning() is called
2843to print a warning message, and then control returns to the calling code.
2844By default png_error() and png_warning() print a message on stderr via
2845fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
2846(because you don't want the messages) or PNG_NO_STDIO defined (because
2847fprintf() isn't available). If you wish to change the behavior of the error
2848functions, you will need to set up your own message callbacks. These
2849functions are normally supplied at the time that the png_struct is created.
2850It is also possible to redirect errors and warnings to your own replacement
2851functions after png_create_*_struct() has been called by calling:
2852
2853 png_set_error_fn(png_structp png_ptr,
2854 png_voidp error_ptr, png_error_ptr error_fn,
2855 png_error_ptr warning_fn);
2856
2857 png_voidp error_ptr = png_get_error_ptr(png_ptr);
2858
2859If NULL is supplied for either error_fn or warning_fn, then the libpng
2860default function will be used, calling fprintf() and/or longjmp() if a
2861problem is encountered. The replacement error functions should have
2862parameters as follows:
2863
2864 void user_error_fn(png_structp png_ptr,
2865 png_const_charp error_msg);
2866 void user_warning_fn(png_structp png_ptr,
2867 png_const_charp warning_msg);
2868
2869The motivation behind using setjmp() and longjmp() is the C++ throw and
2870catch exception handling methods. This makes the code much easier to write,
2871as there is no need to check every return code of every function call.
2872However, there are some uncertainties about the status of local variables
2873after a longjmp, so the user may want to be careful about doing anything after
2874setjmp returns non-zero besides returning itself. Consult your compiler
2875documentation for more details. For an alternative approach, you may wish
2876to use the "cexcept" facility (see http://cexcept.sourceforge.net).
2877
2878.SS Custom chunks
2879
2880If you need to read or write custom chunks, you may need to get deeper
2881into the libpng code. The library now has mechanisms for storing
2882and writing chunks of unknown type; you can even declare callbacks
2883for custom chunks. However, this may not be good enough if the
2884library code itself needs to know about interactions between your
2885chunk and existing `intrinsic' chunks.
2886
2887If you need to write a new intrinsic chunk, first read the PNG
2888specification. Acquire a first level of
2889understanding of how it works. Pay particular attention to the
2890sections that describe chunk names, and look at how other chunks were
2891designed, so you can do things similarly. Second, check out the
2892sections of libpng that read and write chunks. Try to find a chunk
2893that is similar to yours and use it as a template. More details can
2894be found in the comments inside the code. It is best to handle unknown
2895chunks in a generic method, via callback functions, instead of by
2896modifying libpng functions.
2897
2898If you wish to write your own transformation for the data, look through
2899the part of the code that does the transformations, and check out some of
2900the simpler ones to get an idea of how they work. Try to find a similar
2901transformation to the one you want to add and copy off of it. More details
2902can be found in the comments inside the code itself.
2903
2904.SS Configuring for 16 bit platforms
2905
2906You will want to look into zconf.h to tell zlib (and thus libpng) that
2907it cannot allocate more then 64K at a time. Even if you can, the memory
2908won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
2909
2910.SS Configuring for DOS
2911
2912For DOS users who only have access to the lower 640K, you will
2913have to limit zlib's memory usage via a png_set_compression_mem_level()
2914call. See zlib.h or zconf.h in the zlib library for more information.
2915
2916.SS Configuring for Medium Model
2917
2918Libpng's support for medium model has been tested on most of the popular
2919compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
2920defined, and FAR gets defined to far in pngconf.h, and you should be
2921all set. Everything in the library (except for zlib's structure) is
2922expecting far data. You must use the typedefs with the p or pp on
2923the end for pointers (or at least look at them and be careful). Make
2924note that the rows of data are defined as png_bytepp, which is an
2925unsigned char far * far *.
2926
2927.SS Configuring for gui/windowing platforms:
2928
2929You will need to write new error and warning functions that use the GUI
2930interface, as described previously, and set them to be the error and
2931warning functions at the time that png_create_*_struct() is called,
2932in order to have them available during the structure initialization.
2933They can be changed later via png_set_error_fn(). On some compilers,
2934you may also have to change the memory allocators (png_malloc, etc.).
2935
2936.SS Configuring for compiler xxx:
2937
2938All includes for libpng are in pngconf.h. If you need to add/change/delete
2939an include, this is the place to do it. The includes that are not
2940needed outside libpng are protected by the PNG_INTERNAL definition,
2941which is only defined for those routines inside libpng itself. The
2942files in libpng proper only include png.h, which includes pngconf.h.
2943
2944.SS Configuring zlib:
2945
2946There are special functions to configure the compression. Perhaps the
2947most useful one changes the compression level, which currently uses
2948input compression values in the range 0 - 9. The library normally
2949uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
2950have shown that for a large majority of images, compression values in
2951the range 3-6 compress nearly as well as higher levels, and do so much
2952faster. For online applications it may be desirable to have maximum speed
2953(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
2954specify no compression (Z_NO_COMPRESSION = 0), but this would create
2955files larger than just storing the raw bitmap. You can specify the
2956compression level by calling:
2957
2958 png_set_compression_level(png_ptr, level);
2959
2960Another useful one is to reduce the memory level used by the library.
2961The memory level defaults to 8, but it can be lowered if you are
2962short on memory (running DOS, for example, where you only have 640K).
2963Note that the memory level does have an effect on compression; among
2964other things, lower levels will result in sections of incompressible
2965data being emitted in smaller stored blocks, with a correspondingly
2966larger relative overhead of up to 15% in the worst case.
2967
2968 png_set_compression_mem_level(png_ptr, level);
2969
2970The other functions are for configuring zlib. They are not recommended
2971for normal use and may result in writing an invalid PNG file. See
2972zlib.h for more information on what these mean.
2973
2974 png_set_compression_strategy(png_ptr,
2975 strategy);
2976 png_set_compression_window_bits(png_ptr,
2977 window_bits);
2978 png_set_compression_method(png_ptr, method);
2979 png_set_compression_buffer_size(png_ptr, size);
2980
2981.SS Controlling row filtering
2982
2983If you want to control whether libpng uses filtering or not, which
2984filters are used, and how it goes about picking row filters, you
2985can call one of these functions. The selection and configuration
2986of row filters can have a significant impact on the size and
2987encoding speed and a somewhat lesser impact on the decoding speed
2988of an image. Filtering is enabled by default for RGB and grayscale
2989images (with and without alpha), but not for paletted images nor
2990for any images with bit depths less than 8 bits/pixel.
2991
2992The 'method' parameter sets the main filtering method, which is
2993currently only '0' in the PNG 1.2 specification. The 'filters'
2994parameter sets which filter(s), if any, should be used for each
2995scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
2996to turn filtering on and off, respectively.
2997
2998Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
2999PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3000ORed together with '|' to specify one or more filters to use.
3001These filters are described in more detail in the PNG specification.
3002If you intend to change the filter type during the course of writing
3003the image, you should start with flags set for all of the filters
3004you intend to use so that libpng can initialize its internal
3005structures appropriately for all of the filter types. (Note that this
3006means the first row must always be adaptively filtered, because libpng
3007currently does not allocate the filter buffers until png_write_row()
3008is called for the first time.)
3009
3010 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3011 PNG_FILTER_UP | PNG_FILTER_AVE |
3012 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3013
3014 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3015 filters);
3016 The second parameter can also be
3017 PNG_INTRAPIXEL_DIFFERENCING if you are
3018 writing a PNG to be embedded in a MNG
3019 datastream. This parameter must be the
3020 same as the value of filter_method used
3021 in png_set_IHDR().
3022
3023It is also possible to influence how libpng chooses from among the
3024available filters. This is done in one or both of two ways - by
3025telling it how important it is to keep the same filter for successive
3026rows, and by telling it the relative computational costs of the filters.
3027
3028 double weights[3] = {1.5, 1.3, 1.1},
3029 costs[PNG_FILTER_VALUE_LAST] =
3030 {1.0, 1.3, 1.3, 1.5, 1.7};
3031
3032 png_set_filter_heuristics(png_ptr,
3033 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3034 weights, costs);
3035
3036The weights are multiplying factors that indicate to libpng that the
3037row filter should be the same for successive rows unless another row filter
3038is that many times better than the previous filter. In the above example,
3039if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3040"sum of absolute differences" 1.5 x 1.3 times higher than other filters
3041and still be chosen, while the NONE filter could have a sum 1.1 times
3042higher than other filters and still be chosen. Unspecified weights are
3043taken to be 1.0, and the specified weights should probably be declining
3044like those above in order to emphasize recent filters over older filters.
3045
3046The filter costs specify for each filter type a relative decoding cost
3047to be considered when selecting row filters. This means that filters
3048with higher costs are less likely to be chosen over filters with lower
3049costs, unless their "sum of absolute differences" is that much smaller.
3050The costs do not necessarily reflect the exact computational speeds of
3051the various filters, since this would unduly influence the final image
3052size.
3053
3054Note that the numbers above were invented purely for this example and
3055are given only to help explain the function usage. Little testing has
3056been done to find optimum values for either the costs or the weights.
3057
3058.SS Removing unwanted object code
3059
3060There are a bunch of #define's in pngconf.h that control what parts of
3061libpng are compiled. All the defines end in _SUPPORTED. If you are
3062never going to use a capability, you can change the #define to #undef
3063before recompiling libpng and save yourself code and data space, or
3064you can turn off individual capabilities with defines that begin with
3065PNG_NO_.
3066
3067You can also turn all of the transforms and ancillary chunk capabilities
3068off en masse with compiler directives that define
3069PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3070or all four,
3071along with directives to turn on any of the capabilities that you do
3072want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3073the extra transformations but still leave the library fully capable of reading
3074and writing PNG files with all known public chunks
3075Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3076produces a library that is incapable of reading or writing ancillary chunks.
3077If you are not using the progressive reading capability, you can
3078turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3079this with the INTERLACING capability, which you'll still have).
3080
3081All the reading and writing specific code are in separate files, so the
3082linker should only grab the files it needs. However, if you want to
3083make sure, or if you are building a stand alone library, all the
3084reading files start with pngr and all the writing files start with
3085pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3086are used for both reading and writing, and always need to be included.
3087The progressive reader is in pngpread.c
3088
3089If you are creating or distributing a dynamically linked library (a .so
3090or DLL file), you should not remove or disable any parts of the library,
3091as this will cause applications linked with different versions of the
3092library to fail if they call functions not available in your library.
3093The size of the library itself should not be an issue, because only
3094those sections that are actually used will be loaded into memory.
3095
3096.SS Requesting debug printout
3097
3098The macro definition PNG_DEBUG can be used to request debugging
3099printout. Set it to an integer value in the range 0 to 3. Higher
3100numbers result in increasing amounts of debugging information. The
3101information is printed to the "stderr" file, unless another file
3102name is specified in the PNG_DEBUG_FILE macro definition.
3103
3104When PNG_DEBUG > 0, the following functions (macros) become available:
3105
3106 png_debug(level, message)
3107 png_debug1(level, message, p1)
3108 png_debug2(level, message, p1, p2)
3109
3110in which "level" is compared to PNG_DEBUG to decide whether to print
3111the message, "message" is the formatted string to be printed,
3112and p1 and p2 are parameters that are to be embedded in the string
3113according to printf-style formatting directives. For example,
3114
3115 png_debug1(2, "foo=%d\n", foo);
3116
3117is expanded to
3118
3119 if(PNG_DEBUG > 2)
3120 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3121
3122When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3123can still use PNG_DEBUG to control your own debugging:
3124
3125 #ifdef PNG_DEBUG
3126 fprintf(stderr, ...
3127 #endif
3128
3129When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3130having level = 0 will be printed. There aren't any such statements in
3131this version of libpng, but if you insert some they will be printed.
3132
3133.SH VII. MNG support
3134
3135The MNG specification (available at http://www.libpng.org/pub/mng) allows
3136certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3137Libpng can support some of these extensions. To enable them, use the
3138png_permit_mng_features() function:
3139
3140 feature_set = png_permit_mng_features(png_ptr, mask)
3141 mask is a png_uint_32 containing the bitwise OR of the
3142 features you want to enable. These include
3143 PNG_FLAG_MNG_EMPTY_PLTE
3144 PNG_FLAG_MNG_FILTER_64
3145 PNG_ALL_MNG_FEATURES
3146 feature_set is a png_uint_32 that is the bitwise AND of
3147 your mask with the set of MNG features that is
3148 supported by the version of libpng that you are using.
3149
3150It is an error to use this function when reading or writing a standalone
3151PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3152in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3153and the MHDR and MEND chunks. Libpng does not provide support for these
3154or any other MNG chunks; your application must provide its own support for
3155them. You may wish to consider using libmng (available at
3156http://www.libmng.com) instead.
3157
3158.SH VIII. Changes to Libpng from version 0.88
3159
3160It should be noted that versions of libpng later than 0.96 are not
3161distributed by the original libpng author, Guy Schalnat, nor by
3162Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3163distributed versions 0.89 through 0.96, but rather by another member
3164of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3165still alive and well, but they have moved on to other things.
3166
3167The old libpng functions png_read_init(), png_write_init(),
3168png_info_init(), png_read_destroy(), and png_write_destroy() have been
3169moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3170functions will be removed from libpng version 2.0.0.
3171
3172The preferred method of creating and initializing the libpng structures is
3173via the png_create_read_struct(), png_create_write_struct(), and
3174png_create_info_struct() because they isolate the size of the structures
3175from the application, allow version error checking, and also allow the
3176use of custom error handling routines during the initialization, which
3177the old functions do not. The functions png_read_destroy() and
3178png_write_destroy() do not actually free the memory that libpng
3179allocated for these structs, but just reset the data structures, so they
3180can be used instead of png_destroy_read_struct() and
3181png_destroy_write_struct() if you feel there is too much system overhead
3182allocating and freeing the png_struct for each image read.
3183
3184Setting the error callbacks via png_set_message_fn() before
3185png_read_init() as was suggested in libpng-0.88 is no longer supported
3186because this caused applications that do not use custom error functions
3187to fail if the png_ptr was not initialized to zero. It is still possible
3188to set the error callbacks AFTER png_read_init(), or to change them with
3189png_set_error_fn(), which is essentially the same function, but with a new
3190name to force compilation errors with applications that try to use the old
3191method.
3192
3193Starting with version 1.0.7, you can find out which version of the library
3194you are using at run-time:
3195
3196 png_uint_32 libpng_vn = png_access_version_number();
3197
3198The number libpng_vn is constructed from the major version, minor
3199version with leading zero, and release number with leading zero,
3200(e.g., libpng_vn for version 1.0.7 is 10007).
3201
3202You can also check which version of png.h you used when compiling your
3203application:
3204
3205 png_uint_32 application_vn = PNG_LIBPNG_VER;
3206
3207.SH IX. Y2K Compliance in libpng
3208
3209September 8, 2007
3210
3211Since the PNG Development group is an ad-hoc body, we can't make
3212an official declaration.
3213
3214This is your unofficial assurance that libpng from version 0.71 and
3215upward through 1.2.20 are Y2K compliant. It is my belief that earlier
3216versions were also Y2K compliant.
3217
3218Libpng only has three year fields. One is a 2-byte unsigned integer that
3219will hold years up to 65535. The other two hold the date in text
3220format, and will hold years up to 9999.
3221
3222The integer is
3223 "png_uint_16 year" in png_time_struct.
3224
3225The strings are
3226 "png_charp time_buffer" in png_struct and
3227 "near_time_buffer", which is a local character string in png.c.
3228
3229There are seven time-related functions:
3230
3231 png_convert_to_rfc_1123() in png.c
3232 (formerly png_convert_to_rfc_1152() in error)
3233 png_convert_from_struct_tm() in pngwrite.c, called
3234 in pngwrite.c
3235 png_convert_from_time_t() in pngwrite.c
3236 png_get_tIME() in pngget.c
3237 png_handle_tIME() in pngrutil.c, called in pngread.c
3238 png_set_tIME() in pngset.c
3239 png_write_tIME() in pngwutil.c, called in pngwrite.c
3240
3241All appear to handle dates properly in a Y2K environment. The
3242png_convert_from_time_t() function calls gmtime() to convert from system
3243clock time, which returns (year - 1900), which we properly convert to
3244the full 4-digit year. There is a possibility that applications using
3245libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3246function, or that they are incorrectly passing only a 2-digit year
3247instead of "year - 1900" into the png_convert_from_struct_tm() function,
3248but this is not under our control. The libpng documentation has always
3249stated that it works with 4-digit years, and the APIs have been
3250documented as such.
3251
3252The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3253integer to hold the year, and can hold years as large as 65535.
3254
3255zlib, upon which libpng depends, is also Y2K compliant. It contains
3256no date-related code.
3257
3258
3259 Glenn Randers-Pehrson
3260 libpng maintainer
3261 PNG Development Group
3262
3263.SH NOTE
3264
3265Note about libpng version numbers:
3266
3267Due to various miscommunications, unforeseen code incompatibilities
3268and occasional factors outside the authors' control, version numbering
3269on the library has not always been consistent and straightforward.
3270The following table summarizes matters since version 0.89c, which was
3271the first widely used release:
3272
3273 source png.h png.h shared-lib
3274 version string int version
3275 ------- ------ ----- ----------
3276 0.89c ("beta 3") 0.89 89 1.0.89
3277 0.90 ("beta 4") 0.90 90 0.90
3278 0.95 ("beta 5") 0.95 95 0.95
3279 0.96 ("beta 6") 0.96 96 0.96
3280 0.97b ("beta 7") 1.00.97 97 1.0.1
3281 0.97c 0.97 97 2.0.97
3282 0.98 0.98 98 2.0.98
3283 0.99 0.99 98 2.0.99
3284 0.99a-m 0.99 99 2.0.99
3285 1.00 1.00 100 2.1.0
3286 1.0.0 1.0.0 100 2.1.0
3287 1.0.0 (from here on, the 100 2.1.0
3288 1.0.1 png.h string is 10001 2.1.0
3289 1.0.1a-e identical to the 10002 from here on, the
3290 1.0.2 source version) 10002 shared library is 2.V
3291 1.0.2a-b 10003 where V is the source
3292 1.0.1 10001 code version except as
3293 1.0.1a-e 10002 2.1.0.1a-e noted.
3294 1.0.2 10002 2.1.0.2
3295 1.0.2a-b 10003 2.1.0.2a-b
3296 1.0.3 10003 2.1.0.3
3297 1.0.3a-d 10004 2.1.0.3a-d
3298 1.0.4 10004 2.1.0.4
3299 1.0.4a-f 10005 2.1.0.4a-f
3300 1.0.5 (+ 2 patches) 10005 2.1.0.5
3301 1.0.5a-d 10006 2.1.0.5a-d
3302 1.0.5e-r 10100 2.1.0.5e-r
3303 1.0.5s-v 10006 2.1.0.5s-v
3304 1.0.6 (+ 3 patches) 10006 2.1.0.6
3305 1.0.6d-g 10007 2.1.0.6d-g
3306 1.0.6h 10007 10.6h
3307 1.0.6i 10007 10.6i
3308 1.0.6j 10007 2.1.0.6j
3309 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3310 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3311 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3312 1.0.7 1 10007 2.1.0.7
3313 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3314 1.0.8rc1 1 10008 2.1.0.8rc1
3315 1.0.8 1 10008 2.1.0.8
3316 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3317 1.0.9rc1 1 10009 2.1.0.9rc1
3318 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3319 1.0.9rc2 1 10009 2.1.0.9rc2
3320 1.0.9 1 10009 2.1.0.9
3321 1.0.10beta1 1 10010 2.1.0.10beta1
3322 1.0.10rc1 1 10010 2.1.0.10rc1
3323 1.0.10 1 10010 2.1.0.10
3324 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3325 1.0.11rc1 1 10011 2.1.0.11rc1
3326 1.0.11 1 10011 2.1.0.11
3327 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3328 1.0.12rc1 2 10012 2.1.0.12rc1
3329 1.0.12 2 10012 2.1.0.12
3330 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3331 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3332 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3333 1.2.0rc1 3 10200 3.1.2.0rc1
3334 1.2.0 3 10200 3.1.2.0
3335 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3336 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3337 1.2.1 3 10201 3.1.2.1
3338 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3339 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3340 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3341 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3342 1.0.13 10 10013 10.so.0.1.0.13
3343 1.2.2 12 10202 12.so.0.1.2.2
3344 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3345 1.2.3 12 10203 12.so.0.1.2.3
3346 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3347 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3348 1.0.14 10 10014 10.so.0.1.0.14
3349 1.2.4 13 10204 12.so.0.1.2.4
3350 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3351 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3352 1.0.15 10 10015 10.so.0.1.0.15
3353 1.2.5 13 10205 12.so.0.1.2.5
3354 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3355 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3356 1.0.16 10 10016 10.so.0.1.0.16
3357 1.2.6 13 10206 12.so.0.1.2.6
3358 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3359 1.0.17rc1 10 10017 10.so.0.1.0.17rc1
3360 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3361 1.0.17 10 10017 10.so.0.1.0.17
3362 1.2.7 13 10207 12.so.0.1.2.7
3363 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
3364 1.0.18rc1-5 10 10018 10.so.0.1.0.18rc1-5
3365 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
3366 1.0.18 10 10018 10.so.0.1.0.18
3367 1.2.8 13 10208 12.so.0.1.2.8
3368 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
3369 1.2.9beta4-11 13 10209 12.so.0.9[.0]
3370 1.2.9rc1 13 10209 12.so.0.9[.0]
3371 1.2.9 13 10209 12.so.0.9[.0]
3372 1.2.10beta1-8 13 10210 12.so.0.10[.0]
3373 1.2.10rc1-3 13 10210 12.so.0.10[.0]
3374 1.2.10 13 10210 12.so.0.10[.0]
3375 1.2.11beta1-4 13 10211 12.so.0.11[.0]
3376 1.0.19rc1-5 10 10019 10.so.0.19[.0]
3377 1.2.11rc1-5 13 10211 12.so.0.11[.0]
3378 1.0.19 10 10019 10.so.0.19[.0]
3379 1.2.11 13 10211 12.so.0.11[.0]
3380 1.0.20 10 10020 10.so.0.20[.0]
3381 1.2.12 13 10212 12.so.0.12[.0]
3382 1.2.13beta1 13 10213 12.so.0.13[.0]
3383 1.0.21 10 10021 10.so.0.21[.0]
3384 1.2.13 13 10213 12.so.0.13[.0]
3385 1.2.14beta1-2 13 10214 12.so.0.14[.0]
3386 1.0.22rc1 10 10022 10.so.0.22[.0]
3387 1.2.14rc1 13 10214 12.so.0.14[.0]
3388 1.2.15beta1-6 13 10215 12.so.0.15[.0]
3389 1.0.23rc1-5 10 10023 10.so.0.23[.0]
3390 1.2.15rc1-5 13 10215 12.so.0.15[.0]
3391 1.0.23 10 10023 10.so.0.23[.0]
3392 1.2.15 13 10215 12.so.0.15[.0]
3393 1.2.16beta1-2 13 10216 12.so.0.16[.0]
3394 1.2.16rc1 13 10216 12.so.0.16[.0]
3395 1.0.24 10 10024 10.so.0.24[.0]
3396 1.2.16 13 10216 12.so.0.16[.0]
3397 1.2.17beta1-2 13 10217 12.so.0.17[.0]
3398 1.0.25rc1 10 10025 10.so.0.25[.0]
3399 1.2.17rc1-3 13 10217 12.so.0.17[.0]
3400 1.0.25 10 10025 10.so.0.25[.0]
3401 1.2.17 13 10217 12.so.0.17[.0]
3402 1.0.26 10 10026 10.so.0.26[.0]
3403 1.2.18 13 10218 12.so.0.18[.0]
3404 1.2.19beta1-31 13 10219 12.so.0.19[.0]
3405 1.0.27rc1-6 10 10027 10.so.0.27[.0]
3406 1.2.19rc1-6 13 10219 12.so.0.19[.0]
3407 1.0.27 10 10027 10.so.0.27[.0]
3408 1.2.19 13 10219 12.so.0.19[.0]
3409 1.2.20beta01-04 13 10220 12.so.0.20[.0]
3410 1.0.28rc1-6 10 10028 10.so.0.28[.0]
3411 1.2.20rc1-6 13 10220 12.so.0.20[.0]
3412 1.0.28 10 10028 10.so.0.28[.0]
3413 1.2.20 13 10220 12.so.0.20[.0]
3414
3415Henceforth the source version will match the shared-library minor
3416and patch numbers; the shared-library major version number will be
3417used for changes in backward compatibility, as it is intended. The
3418PNG_PNGLIB_VER macro, which is not used within libpng but is available
3419for applications, is an unsigned integer of the form xyyzz corresponding
3420to the source version x.y.z (leading zeros in y and z). Beta versions
3421were given the previous public release number plus a letter, until
3422version 1.0.6j; from then on they were given the upcoming public
3423release number plus "betaNN" or "rcN".
3424
3425.SH "SEE ALSO"
3426.IR libpngpf(3) ", " png(5)
3427.LP
3428.IR libpng :
3429.IP
3430http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3431http://www.libpng.org/pub/png
3432
3433.LP
3434.IR zlib :
3435.IP
3436(generally) at the same location as
3437.I libpng
3438or at
3439.br
3440ftp://ftp.info-zip.org/pub/infozip/zlib
3441
3442.LP
3443.IR PNG specification: RFC 2083
3444.IP
3445(generally) at the same location as
3446.I libpng
3447or at
3448.br
3449ftp://ds.internic.net/rfc/rfc2083.txt
3450.br
3451or (as a W3C Recommendation) at
3452.br
3453http://www.w3.org/TR/REC-png.html
3454
3455.LP
3456In the case of any inconsistency between the PNG specification
3457and this library, the specification takes precedence.
3458
3459.SH AUTHORS
3460This man page: Glenn Randers-Pehrson
3461<glennrp at users.sourceforge.net>
3462
3463The contributing authors would like to thank all those who helped
3464with testing, bug fixes, and patience. This wouldn't have been
3465possible without all of you.
3466
3467Thanks to Frank J. T. Wojcik for helping with the documentation.
3468
3469Libpng version 1.2.20 - September 8, 2007:
3470Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3471Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
3472
3473Supported by the PNG development group
3474.br
3475png-mng-implement at lists.sf.net
3476(subscription required; visit
3477png-mng-implement at lists.sourceforge.net (subscription required; visit
3478https://lists.sourceforge.net/lists/listinfo/png-mng-implement
3479to subscribe).
3480
3481.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3482
3483(This copy of the libpng notices is provided for your convenience. In case of
3484any discrepancy between this copy and the notices in the file png.h that is
3485included in the libpng distribution, the latter shall prevail.)
3486
3487If you modify libpng you may insert additional notices immediately following
3488this sentence.
3489
3490libpng versions 1.2.6, August 15, 2004, through 1.2.20, September 8, 2007, are
3491Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
3492distributed according to the same disclaimer and license as libpng-1.2.5
3493with the following individual added to the list of Contributing Authors
3494
3495 Cosmin Truta
3496
3497libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
3498Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3499distributed according to the same disclaimer and license as libpng-1.0.6
3500with the following individuals added to the list of Contributing Authors
3501
3502 Simon-Pierre Cadieux
3503 Eric S. Raymond
3504 Gilles Vollant
3505
3506and with the following additions to the disclaimer:
3507
3508 There is no warranty against interference with your
3509 enjoyment of the library or against infringement.
3510 There is no warranty that our efforts or the library
3511 will fulfill any of your particular purposes or needs.
3512 This library is provided with all faults, and the entire
3513 risk of satisfactory quality, performance, accuracy, and
3514 effort is with the user.
3515
3516libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3517Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3518Distributed according to the same disclaimer and license as libpng-0.96,
3519with the following individuals added to the list of Contributing Authors:
3520
3521 Tom Lane
3522 Glenn Randers-Pehrson
3523 Willem van Schaik
3524
3525libpng versions 0.89, June 1996, through 0.96, May 1997, are
3526Copyright (c) 1996, 1997 Andreas Dilger
3527Distributed according to the same disclaimer and license as libpng-0.88,
3528with the following individuals added to the list of Contributing Authors:
3529
3530 John Bowler
3531 Kevin Bracey
3532 Sam Bushell
3533 Magnus Holmgren
3534 Greg Roelofs
3535 Tom Tanner
3536
3537libpng versions 0.5, May 1995, through 0.88, January 1996, are
3538Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3539
3540For the purposes of this copyright and license, "Contributing Authors"
3541is defined as the following set of individuals:
3542
3543 Andreas Dilger
3544 Dave Martindale
3545 Guy Eric Schalnat
3546 Paul Schmidt
3547 Tim Wegner
3548
3549The PNG Reference Library is supplied "AS IS". The Contributing Authors
3550and Group 42, Inc. disclaim all warranties, expressed or implied,
3551including, without limitation, the warranties of merchantability and of
3552fitness for any purpose. The Contributing Authors and Group 42, Inc.
3553assume no liability for direct, indirect, incidental, special, exemplary,
3554or consequential damages, which may result from the use of the PNG
3555Reference Library, even if advised of the possibility of such damage.
3556
3557Permission is hereby granted to use, copy, modify, and distribute this
3558source code, or portions hereof, for any purpose, without fee, subject
3559to the following restrictions:
3560
35611. The origin of this source code must not be misrepresented.
3562
35632. Altered versions must be plainly marked as such and
3564 must not be misrepresented as being the original source.
3565
35663. This Copyright notice may not be removed or altered from
3567 any source or altered source distribution.
3568
3569The Contributing Authors and Group 42, Inc. specifically permit, without
3570fee, and encourage the use of this source code as a component to
3571supporting the PNG file format in commercial products. If you use this
3572source code in a product, acknowledgment is not required but would be
3573appreciated.
3574
3575
3576A "png_get_copyright" function is available, for convenient use in "about"
3577boxes and the like:
3578
3579 printf("%s",png_get_copyright(NULL));
3580
3581Also, the PNG logo (in PNG format, of course) is supplied in the
3582files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
3583
3584Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
3585certification mark of the Open Source Initiative.
3586
3587Glenn Randers-Pehrson
3588glennrp at users.sourceforge.net
3589September 8, 2007
3590
3591.\" end of man page
3592
wxWidgets (Impactor)