1README for libpng version 1.6.44
2================================
3
4See the note about version numbers near the top of `png.h`.
5See `INSTALL` for instructions on how to install libpng.
6
7Libpng comes in several distribution formats. Get `libpng-*.tar.gz`
8or `libpng-*.tar.xz` if you want UNIX-style line endings in the text
9files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings.
10
11For a detailed description on using libpng, read `libpng-manual.txt`.
12For examples of libpng in a program, see `example.c` and `pngtest.c`.
13For usage information and restrictions (what little they are) on libpng,
14see `png.h`. For a description on using zlib (the compression library
15used by libpng) and zlib's restrictions, see `zlib.h`.
16
17You should use zlib 1.0.4 or later to run this, but it _may_ work with
18versions as old as zlib 0.95. Even so, there are bugs in older zlib
19versions which can cause the output of invalid compression streams for
20some images.
21
22You should also note that zlib is a compression library that is useful
23for more things than just PNG files. You can use zlib as a drop-in
24replacement for `fread()` and `fwrite()`, if you are so inclined.
25
26zlib should be available at the same place that libpng is, or at
27https://zlib.net .
28
29You may also want a copy of the PNG specification. It is available
30as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
31these at http://www.libpng.org/pub/png/pngdocs.html .
32
33This code is currently being archived at https://libpng.sourceforge.io
34in the download area, and at http://libpng.download/src .
35
36This release, based in a large way on Glenn's, Guy's and Andreas'
37earlier work, was created and will be supported by myself and the PNG
38development group.
39
40Send comments, corrections and commendations to `png-mng-implement`
41at `lists.sourceforge.net`. (Subscription is required; visit
42https://lists.sourceforge.net/lists/listinfo/png-mng-implement
43to subscribe.)
44
45Send general questions about the PNG specification to `png-mng-misc`
46at `lists.sourceforge.net`. (Subscription is required; visit
47https://lists.sourceforge.net/lists/listinfo/png-mng-misc
48to subscribe.)
49
50Historical notes
51----------------
52
53The libpng library has been in extensive use and testing since mid-1995.
54Version 0.89, published a year later, was the first official release.
55By late 1997, it had finally gotten to the stage where there hadn't
56been significant changes to the API in some time, and people have a bad
57feeling about libraries with versions below 1.0. Version 1.0.0 was
58released in March 1998.
59
60Note that some of the changes to the `png_info` structure render this
61version of the library binary incompatible with libpng-0.89 or
62earlier versions if you are using a shared library. The type of the
63`filler` parameter for `png_set_filler()` has changed from `png_byte`
64to `png_uint_32`, which will affect shared-library applications that
65use this function.
66
67To avoid problems with changes to the internals of the `info_struct`,
68new APIs have been made available in 0.95 to avoid direct application
69access to `info_ptr`. These functions are the `png_set_<chunk>` and
70`png_get_<chunk>` functions. These functions should be used when
71accessing/storing the `info_struct` data, rather than manipulating it
72directly, to avoid such problems in the future.
73
74It is important to note that the APIs did not make current programs
75that access the info struct directly incompatible with the new
76library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
77be a transitional release, members of the `png_struct` and the
78`info_struct` can still be accessed, but the compiler will issue a
79warning about deprecated usage. Since libpng-1.5.0, direct access
80to these structs is not allowed, and the definitions of the structs
81reside in private `pngstruct.h` and `pnginfo.h` header files that are
82not accessible to applications. It is strongly suggested that new
83programs use the new APIs (as shown in `example.c` and `pngtest.c`),
84and older programs be converted to the new format, to facilitate
85upgrades in the future.
86
87The additions since 0.89 include the ability to read from a PNG stream
88which has had some (or all) of the signature bytes read by the calling
89application. This also allows the reading of embedded PNG streams that
90do not have the PNG file signature. As well, it is now possible to set
91the library action on the detection of chunk CRC errors. It is possible
92to set different actions based on whether the CRC error occurred in a
93critical or an ancillary chunk.
94
95The additions since 0.90 include the ability to compile libpng as a
96Windows DLL, and new APIs for accessing data in the `info_struct`.
97Experimental functions included the ability to set weighting and cost
98factors for row filter selection, direct reads of integers from buffers
99on big-endian processors that support misaligned data access, faster
100methods of doing alpha composition, and more accurate 16-to-8 bit color
101conversion. Some of these experimental functions, such as the weighted
102filter heuristics, have since been removed.
103
104Files included in this distribution
105-----------------------------------
106
107 ANNOUNCE => Announcement of this version, with recent changes
108 AUTHORS => List of contributing authors
109 CHANGES => Description of changes between libpng versions
110 INSTALL => Instructions to install libpng
111 LICENSE => License to use and redistribute libpng
112 README => This file
113 TODO => Things not implemented in the current library
114 TRADEMARK => Trademark information
115 example.c => Example code for using libpng functions
116 libpng.3 => Manual page for libpng (includes libpng-manual.txt)
117 libpng-manual.txt => Description of libpng and its functions
118 libpngpf.3 => Manual page for libpng's private functions (deprecated)
119 png.5 => Manual page for the PNG format
120 png.c => Basic interface functions common to library
121 png.h => Library function and interface declarations (public)
122 pngpriv.h => Library function and interface declarations (private)
123 pngconf.h => System specific library configuration (public)
124 pngstruct.h => png_struct declaration (private)
125 pnginfo.h => png_info struct declaration (private)
126 pngdebug.h => debugging macros (private)
127 pngerror.c => Error/warning message I/O functions
128 pngget.c => Functions for retrieving info from struct
129 pngmem.c => Memory handling functions
130 pngbar.png => PNG logo, 88x31
131 pngnow.png => PNG logo, 98x31
132 pngpread.c => Progressive reading functions
133 pngread.c => Read data/helper high-level functions
134 pngrio.c => Lowest-level data read I/O functions
135 pngrtran.c => Read data transformation functions
136 pngrutil.c => Read data utility functions
137 pngset.c => Functions for storing data into the info_struct
138 pngtest.c => Library test program
139 pngtest.png => Library test sample image
140 pngtrans.c => Common data transformation functions
141 pngwio.c => Lowest-level write I/O functions
142 pngwrite.c => High-level write functions
143 pngwtran.c => Write data transformations
144 pngwutil.c => Write utility functions
145 arm/ => Optimized code for ARM Neon
146 intel/ => Optimized code for INTEL SSE2
147 loongarch/ => Optimized code for LoongArch LSX
148 mips/ => Optimized code for MIPS MSA and MIPS MMI
149 powerpc/ => Optimized code for PowerPC VSX
150 ci/ => Scripts for continuous integration
151 contrib/ => External contributions
152 arm-neon/ => Optimized code for the ARM-NEON platform
153 mips-msa/ => Optimized code for the MIPS-MSA platform
154 powerpc-vsx/ => Optimized code for the POWERPC-VSX platform
155 examples/ => Examples of libpng usage
156 gregbook/ => Source code for PNG reading and writing, from
157 "PNG: The Definitive Guide" by Greg Roelofs,
158 O'Reilly, 1999
159 libtests/ => Test programs
160 oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing
161 libpng
162 pngexif/ => Program to inspect the EXIF information in PNG files
163 pngminim/ => Minimal decoder, encoder, and progressive decoder
164 programs demonstrating the use of pngusr.dfa
165 pngminus/ => Simple pnm2png and png2pnm programs
166 pngsuite/ => Test images
167 testpngs/ => Test images
168 tools/ => Various tools
169 visupng/ => VisualPng, a Windows viewer for PNG images
170 projects/ => Project files and workspaces for various IDEs
171 owatcom/ => OpenWatcom project
172 visualc71/ => Microsoft Visual C++ 7.1 workspace
173 vstudio/ => Microsoft Visual Studio workspace
174 scripts/ => Scripts and makefiles for building libpng
175 (see scripts/README.txt for the complete list)
176 tests/ => Test scripts
177
178Good luck, and happy coding!
179
180 * Cosmin Truta (current maintainer, since 2018)
181 * Glenn Randers-Pehrson (former maintainer, 1998-2018)
182 * Andreas Eric Dilger (former maintainer, 1996-1997)
183 * Guy Eric Schalnat (original author and former maintainer, 1995-1996)
184 (formerly of Group 42, Inc.)
185
