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1 README for libpng version 1.6.37 - April 14, 2019
4 See the note about version numbers near the top of png.h.
5 See INSTALL for instructions on how to install libpng.
7 Libpng comes in several distribution formats. Get libpng-*.tar.gz or
8 libpng-*.tar.xz or if you want UNIX-style line endings in the text
9 files, or lpng*.7z or lpng*.zip if you want DOS-style line endings.
11 Version 0.89 was the first official release of libpng. Don't let the
12 fact that it's the first release fool you. The libpng library has been
13 in extensive use and testing since mid-1995. By late 1997 it had
14 finally gotten to the stage where there hadn't been significant
15 changes to the API in some time, and people have a bad feeling about
16 libraries with versions < 1.0. Version 1.0.0 was released in
17 March 1998.
20 Note that some of the changes to the png_info structure render this
21 version of the library binary incompatible with libpng-0.89 or
22 earlier 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
24 png_uint_32, which will affect shared-library applications that use
25 this function.
27 To avoid problems with changes to the internals of the png info_struct,
28 new APIs have been made available in 0.95 to avoid direct application
29 access to info_ptr. These functions are the png_set_<chunk> and
30 png_get_<chunk> functions. These functions should be used when
31 accessing/storing the info_struct data, rather than manipulating it
32 directly, to avoid such problems in the future.
34 It is important to note that the APIs did not make current programs
35 that access the info struct directly incompatible with the new
36 library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
37 be a transitional release, members of the png_struct and the
38 info_struct can still be accessed, but the compiler will issue a
39 warning about deprecated usage. Since libpng-1.5.0, direct access
40 to these structs is not allowed, and the definitions of the structs
41 reside in private pngstruct.h and pnginfo.h header files that are not
42 accessible to applications. It is strongly suggested that new
43 programs use the new APIs (as shown in example.c and pngtest.c), and
44 older programs be converted to the new format, to facilitate upgrades
45 in the future.
48 Additions since 0.90 include the ability to compile libpng as a
49 Windows DLL, and new APIs for accessing data in the info struct.
50 Experimental functions include the ability to set weighting and cost
51 factors for row filter selection, direct reads of integers from buffers
52 on big-endian processors that support misaligned data access, faster
53 methods of doing alpha composition, and more accurate 16->8 bit color
56 The additions since 0.89 include the ability to read from a PNG stream
57 which has had some (or all) of the signature bytes read by the calling
58 application. This also allows the reading of embedded PNG streams that
59 do not have the PNG file signature. As well, it is now possible to set
60 the library action on the detection of chunk CRC errors. It is possible
61 to set different actions based on whether the CRC error occurred in a
62 critical or an ancillary chunk.
64 For a detailed description on using libpng, read libpng-manual.txt.
65 For examples of libpng in a program, see example.c and pngtest.c. For
66 usage information and restrictions (what little they are) on libpng,
67 see png.h. For a description on using zlib (the compression library
68 used by libpng) and zlib's restrictions, see zlib.h
70 I have included a general makefile, as well as several machine and
71 compiler specific ones, but you may have to modify one for your own
74 You should use zlib 1.0.4 or later to run this, but it MAY work with
75 versions as old as zlib 0.95. Even so, there are bugs in older zlib
76 versions which can cause the output of invalid compression streams for
77 some images.
79 You should also note that zlib is a compression library that is useful
80 for more things than just PNG files. You can use zlib as a drop-in
81 replacement for fread() and fwrite(), if you are so inclined.
83 zlib should be available at the same place that libpng is, or at
86 You may also want a copy of the PNG specification. It is available
87 as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
88 these at http://www.libpng.org/pub/png/pngdocs.html .
90 This code is currently being archived at libpng.sourceforge.io in the
91 [DOWNLOAD] area, and at http://libpng.download/src .
93 This release, based in a large way on Glenn's, Guy's and Andreas'
94 earlier work, was created and will be supported by myself and the PNG
95 development group.
97 Send comments/corrections/commendations to png-mng-implement at
98 lists.sourceforge.net (subscription required; visit
100 to subscribe).
102 Send general questions about the PNG specification to png-mng-misc
103 at lists.sourceforge.net (subscription required; visit
104 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
107 Files in this distribution:
109 ANNOUNCE => Announcement of this version, with recent changes
110 AUTHORS => List of contributing authors
111 CHANGES => Description of changes between libpng versions
112 KNOWNBUG => List of known bugs and deficiencies
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
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 => Contains optimized code for the ARM platform
148 powerpc => Contains optimized code for the PowerPC platform
149 contrib => Contributions
150 arm-neon => Optimized code for ARM-NEON platform
151 powerpc-vsx => Optimized code for POWERPC-VSX platform
152 examples => Example programs
153 gregbook => source code for PNG reading and writing, from
154 Greg Roelofs' "PNG: The Definitive Guide",
155 O'Reilly, 1999
156 libtests => Test programs
157 mips-msa => Optimized code for MIPS-MSA platform
158 pngminim => Minimal decoder, encoder, and progressive decoder
159 programs demonstrating use of pngusr.dfa
160 pngminus => Simple pnm2png and png2pnm programs
161 pngsuite => Test images
163 tools => Various tools
164 visupng => Contains a MSVC workspace for VisualPng
165 intel => Optimized code for INTEL-SSE2 platform
166 mips => Optimized code for MIPS platform
167 projects => Contains project files and workspaces for
168 building a DLL
169 owatcom => Contains a WATCOM project for building libpng
170 visualc71 => Contains a Microsoft Visual C++ (MSVC)
171 workspace for building libpng and zlib
172 vstudio => Contains a Microsoft Visual C++ (MSVC)
173 workspace for building libpng and zlib
174 scripts => Directory containing scripts for building libpng:
175 (see scripts/README.txt for the list of scripts)
177 Good luck, and happy coding!
179 * Cosmin Truta (current maintainer, since 2018)
180 * Glenn Randers-Pehrson (former maintainer, 1998-2018)
181 * Andreas Eric Dilger (former maintainer, 1996-1997)
182 * Guy Eric Schalnat (original author and former maintainer, 1995-1996)
183 (formerly of Group 42, Inc.)