1README for libpng version 1.6.39
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 or
8libpng-*.tar.xz if you want UNIX-style line endings in the text files,
9or lpng*.7z or lpng*.zip if you want DOS-style line endings.
10
11Version 0.89 was the first official release of libpng. Don't let the
12fact that it's the first release fool you. The libpng library has been
13in extensive use and testing since mid-1995. By late 1997 it had
14finally gotten to the stage where there hadn't been significant
15changes to the API in some time, and people have a bad feeling about
16libraries with versions < 1.0. Version 1.0.0 was released in
17March 1998.
18
19****
20Note that some of the changes to the png_info structure render this
21version of the library binary incompatible with libpng-0.89 or
22earlier versions if you are using a shared library. The type of the
23"filler" parameter for png_set_filler() has changed from png_byte to
24png_uint_32, which will affect shared-library applications that use
25this function.
26
27To avoid problems with changes to the internals of the png info_struct,
28new APIs have been made available in 0.95 to avoid direct application
29access to info_ptr. These functions are the png_set_<chunk> and
30png_get_<chunk> functions. These functions should be used when
31accessing/storing the info_struct data, rather than manipulating it
32directly, to avoid such problems in the future.
33
34It is important to note that the APIs did not make current programs
35that access the info struct directly incompatible with the new
36library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
37be a transitional release, members of the png_struct and the
38info_struct can still be accessed, but the compiler will issue a
39warning about deprecated usage. Since libpng-1.5.0, direct access
40to these structs is not allowed, and the definitions of the structs
41reside in private pngstruct.h and pnginfo.h header files that are not
42accessible to applications. It is strongly suggested that new
43programs use the new APIs (as shown in example.c and pngtest.c), and
44older programs be converted to the new format, to facilitate upgrades
45in the future.
46****
47
48Additions since 0.90 include the ability to compile libpng as a
49Windows DLL, and new APIs for accessing data in the info struct.
50Experimental functions include the ability to set weighting and cost
51factors for row filter selection, direct reads of integers from buffers
52on big-endian processors that support misaligned data access, faster
53methods of doing alpha composition, and more accurate 16->8 bit color
54conversion.
55
56The additions since 0.89 include the ability to read from a PNG stream
57which has had some (or all) of the signature bytes read by the calling
58application. This also allows the reading of embedded PNG streams that
59do not have the PNG file signature. As well, it is now possible to set
60the library action on the detection of chunk CRC errors. It is possible
61to set different actions based on whether the CRC error occurred in a
62critical or an ancillary chunk.
63
64For a detailed description on using libpng, read libpng-manual.txt.
65For examples of libpng in a program, see example.c and pngtest.c. For
66usage information and restrictions (what little they are) on libpng,
67see png.h. For a description on using zlib (the compression library
68used by libpng) and zlib's restrictions, see zlib.h
69
70I have included a general makefile, as well as several machine and
71compiler specific ones, but you may have to modify one for your own
72needs.
73
74You should use zlib 1.0.4 or later to run this, but it MAY work with
75versions as old as zlib 0.95. Even so, there are bugs in older zlib
76versions which can cause the output of invalid compression streams for
77some images.
78
79You should also note that zlib is a compression library that is useful
80for more things than just PNG files. You can use zlib as a drop-in
81replacement for fread() and fwrite(), if you are so inclined.
82
83zlib should be available at the same place that libpng is, or at
84https://zlib.net.
85
86You may also want a copy of the PNG specification. It is available
87as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
88these at http://www.libpng.org/pub/png/pngdocs.html .
89
90This code is currently being archived at libpng.sourceforge.io in the
91[DOWNLOAD] area, and at http://libpng.download/src .
92
93This release, based in a large way on Glenn's, Guy's and Andreas'
94earlier work, was created and will be supported by myself and the PNG
95development group.
96
97Send comments/corrections/commendations to png-mng-implement at
98lists.sourceforge.net (subscription required; visit
99https://lists.sourceforge.net/lists/listinfo/png-mng-implement
100to subscribe).
101
102Send general questions about the PNG specification to png-mng-misc
103at lists.sourceforge.net (subscription required; visit
104https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
105subscribe).
106
107Files in this distribution:
108
109 ANNOUNCE => Announcement of this version, with recent changes
110 AUTHORS => List of contributing authors
111 CHANGES => Description of changes between libpng versions
112 INSTALL => Instructions to install libpng
113 LICENSE => License to use and redistribute libpng
114 README => This file
115 TODO => Things not implemented in the current library
116 TRADEMARK => Trademark information
117 example.c => Example code for using libpng functions
118 libpng.3 => Manual page for libpng (includes libpng-manual.txt)
119 libpng-manual.txt => Description of libpng and its functions
120 libpngpf.3 => Manual page for libpng's private functions (deprecated)
121 png.5 => Manual page for the PNG format
122 png.c => Basic interface functions common to library
123 png.h => Library function and interface declarations (public)
124 pngpriv.h => Library function and interface declarations (private)
125 pngconf.h => System specific library configuration (public)
126 pngstruct.h => png_struct declaration (private)
127 pnginfo.h => png_info struct declaration (private)
128 pngdebug.h => debugging macros (private)
129 pngerror.c => Error/warning message I/O functions
130 pngget.c => Functions for retrieving info from struct
131 pngmem.c => Memory handling functions
132 pngbar.png => PNG logo, 88x31
133 pngnow.png => PNG logo, 98x31
134 pngpread.c => Progressive reading functions
135 pngread.c => Read data/helper high-level functions
136 pngrio.c => Lowest-level data read I/O functions
137 pngrtran.c => Read data transformation functions
138 pngrutil.c => Read data utility functions
139 pngset.c => Functions for storing data into the info_struct
140 pngtest.c => Library test program
141 pngtest.png => Library test sample image
142 pngtrans.c => Common data transformation functions
143 pngwio.c => Lowest-level write I/O functions
144 pngwrite.c => High-level write functions
145 pngwtran.c => Write data transformations
146 pngwutil.c => Write utility functions
147 arm/ => Optimized code for the ARM platform
148 intel/ => Optimized code for the INTEL-SSE2 platform
149 mips/ => Optimized code for the MIPS platform
150 powerpc/ => Optimized code for the PowerPC platform
151 ci/ => Scripts for continuous integration
152 contrib/ => External contributions
153 arm-neon/ => Optimized code for the ARM-NEON platform
154 mips-msa/ => Optimized code for the MIPS-MSA platform
155 powerpc-vsx/ => Optimized code for the POWERPC-VSX platform
156 examples/ => Example programs
157 gregbook/ => Source code for PNG reading and writing, from
158 "PNG: The Definitive Guide" by Greg Roelofs,
159 O'Reilly, 1999
160 libtests/ => Test programs
161 oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing
162 libpng
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
