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Possible License(s): AGPL-3.0, LGPL-2.1, LGPL-3.0, GPL-2.0
  1README for libpng version 1.5.4 - July 7, 2011 (shared library 15.0)
  2See the note about version numbers near the top of png.h
  4See INSTALL for instructions on how to install libpng.
  6Libpng comes in several distribution formats.  Get libpng-*.tar.gz,
  7libpng-*.tar.xz or libpng-*.tar.bz2 if you want UNIX-style line endings
  8in the text files, or lpng*.zip if you want DOS-style line endings.
 10Version 0.89 was the first official release of libpng.  Don't let the
 11fact that it's the first release fool you.  The libpng library has been in
 12extensive use and testing since mid-1995.  By late 1997 it had
 13finally gotten to the stage where there hadn't been significant
 14changes to the API in some time, and people have a bad feeling about
 15libraries with versions < 1.0.  Version 1.0.0 was released in
 16March 1998.
 19Note that some of the changes to the png_info structure render this
 20version of the library binary incompatible with libpng-0.89 or
 21earlier versions if you are using a shared library.  The type of the
 22"filler" parameter for png_set_filler() has changed from png_byte to
 23png_uint_32, which will affect shared-library applications that use
 24this function.
 26To avoid problems with changes to the internals of png_info_struct,
 27new APIs have been made available in 0.95 to avoid direct application
 28access to info_ptr.  These functions are the png_set_<chunk> and
 29png_get_<chunk> functions.  These functions should be used when
 30accessing/storing the info_struct data, rather than manipulating it
 31directly, to avoid such problems in the future.
 33It is important to note that the APIs do not make current programs
 34that access the info struct directly incompatible with the new
 35library.  However, it is strongly suggested that new programs use
 36the new APIs (as shown in example.c and pngtest.c), and older programs
 37be converted to the new format, to facilitate upgrades in the future.
 40Additions since 0.90 include the ability to compile libpng as a
 41Windows DLL, and new APIs for accessing data in the info struct.
 42Experimental functions include the ability to set weighting and cost
 43factors for row filter selection, direct reads of integers from buffers
 44on big-endian processors that support misaligned data access, faster
 45methods of doing alpha composition, and more accurate 16->8 bit color
 48The additions since 0.89 include the ability to read from a PNG stream
 49which has had some (or all) of the signature bytes read by the calling
 50application.  This also allows the reading of embedded PNG streams that
 51do not have the PNG file signature.  As well, it is now possible to set
 52the library action on the detection of chunk CRC errors.  It is possible
 53to set different actions based on whether the CRC error occurred in a
 54critical or an ancillary chunk.
 56The changes made to the library, and bugs fixed are based on discussions
 57on the PNG-implement mailing list and not on material submitted
 58privately to Guy, Andreas, or Glenn.  They will forward any good
 59suggestions to the list.
 61For a detailed description on using libpng, read libpng-manual.txt.  For
 62examples of libpng in a program, see example.c and pngtest.c.  For usage
 63information and restrictions (what little they are) on libpng, see
 64png.h.  For a description on using zlib (the compression library used by
 65libpng) and zlib's restrictions, see zlib.h
 67I have included a general makefile, as well as several machine and
 68compiler specific ones, but you may have to modify one for your own needs.
 70You should use zlib 1.0.4 or later to run this, but it MAY work with
 71versions as old as zlib 0.95.  Even so, there are bugs in older zlib
 72versions which can cause the output of invalid compression streams for
 73some images.  You will definitely need zlib 1.0.4 or later if you are
 74taking advantage of the MS-DOS "far" structure allocation for the small
 75and medium memory models.  You should also note that zlib is a
 76compression library that is useful for more things than just PNG files.
 77You can use zlib as a drop-in replacement for fread() and fwrite() if
 78you are so inclined.
 80zlib should be available at the same place that libpng is, or at.
 83You may also want a copy of the PNG specification.  It is available
 84as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
 85these at
 87This code is currently being archived at in the
 88[DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT)
 89at GO GRAPHSUP.  If you can't find it in any of those places,
 90e-mail me, and I'll help you find it.
 92If you have any code changes, requests, problems, etc., please e-mail
 93them to me.  Also, I'd appreciate any make files or project files,
 94and any modifications you needed to make to get libpng to compile,
 95along with a #define variable to tell what compiler/system you are on.
 96If you needed to add transformations to libpng, or wish libpng would
 97provide the image in a different way, drop me a note (and code, if
 98possible), so I can consider supporting the transformation.
 99Finally, if you get any warning messages when compiling libpng
100(note: not zlib), and they are easy to fix, I'd appreciate the
101fix.  Please mention "libpng" somewhere in the subject line.  Thanks.
103This release was created and will be supported by myself (of course
104based in a large way on Guy's and Andreas' earlier work), and the PNG
105development group.
107Send comments/corrections/commendations to png-mng-implement at (subscription required; visit 
110to subscribe) or to glennrp at
112You can't reach Guy, the original libpng author, at the addresses
113given in previous versions of this document.  He and Andreas will
114read mail addressed to the png-implement list, however.
116Please do not send general questions about PNG.  Send them to
117png-mng-misc at (subscription required; visit
118 to
119subscribe).  If you have a question about something
120in the PNG specification that is related to using libpng, send it
121to me.  Send me any questions that start with "I was using libpng,
122and ...".  If in doubt, send questions to me.  I'll bounce them
123to others, if necessary.
125Please do not send suggestions on how to change PNG.  We have
126been discussing PNG for sixteen years now, and it is official and
127finished.  If you have suggestions for libpng, however, I'll
128gladly listen.  Even if your suggestion is not used immediately,
129it may be used later.
131Files in this distribution:
133      ANNOUNCE      =>  Announcement of this version, with recent changes
134      CHANGES       =>  Description of changes between libpng versions
135      KNOWNBUG      =>  List of known bugs and deficiencies
136      LICENSE       =>  License to use and redistribute libpng
137      README        =>  This file
138      TODO          =>  Things not implemented in the current library
139      Y2KINFO       =>  Statement of Y2K compliance
140      example.c     =>  Example code for using libpng functions
141      libpng.3      =>  manual page for libpng (includes libpng-manual.txt)
142      libpng-manual.txt  =>  Description of libpng and its functions
143      libpngpf.3    =>  manual page for libpng's private functions
144      png.5         =>  manual page for the PNG format
145      png.c         =>  Basic interface functions common to library
146      png.h         =>  Library function and interface declarations (public)
147      pngpriv.h     =>  Library function and interface declarations (private)
148      pngconf.h     =>  System specific library configuration (public)
149      pngstruct.h   =>  png_struct declaration (private)
150      pnginfo.h     =>  png_info struct declaration (private)
151      pngdebug.h    =>  debugging macros (private)
152      pngerror.c    =>  Error/warning message I/O functions
153      pngget.c      =>  Functions for retrieving info from struct
154      pngmem.c      =>  Memory handling functions
155      pngbar.png    =>  PNG logo, 88x31
156      pngnow.png    =>  PNG logo, 98x31
157      pngpread.c    =>  Progressive reading functions
158      pngread.c     =>  Read data/helper high-level functions
159      pngrio.c      =>  Lowest-level data read I/O functions
160      pngrtran.c    =>  Read data transformation functions
161      pngrutil.c    =>  Read data utility functions
162      pngset.c      =>  Functions for storing data into the info_struct
163      pngtest.c     =>  Library test program
164      pngtest.png   =>  Library test sample image
165      pngtrans.c    =>  Common data transformation functions
166      pngwio.c      =>  Lowest-level write I/O functions
167      pngwrite.c    =>  High-level write functions
168      pngwtran.c    =>  Write data transformations
169      pngwutil.c    =>  Write utility functions
170      contrib       =>  Contributions
171       gregbook         =>  source code for PNG reading and writing, from
172                            Greg Roelofs' "PNG: The Definitive Guide",
173                            O'Reilly, 1999
174       msvctest     =>  Builds and runs pngtest using a MSVC workspace
175       pngminus     =>  Simple pnm2png and png2pnm programs
176       pngsuite     =>  Test images
177       visupng      =>  Contains a MSVC workspace for VisualPng
178      projects      =>  Contains project files and workspaces for
179                        building a DLL
180       cbuilder5        =>  Contains a Borland workspace for building
181                            libpng and zlib
182       visualc6         =>  Contains a Microsoft Visual C++ (MSVC)
183                            workspace for building libpng and zlib
184       visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
185                            workspace for building libpng and zlib
186       xcode            =>  Contains an Apple xcode
187                            workspace for building libpng and zlib
188      scripts       =>  Directory containing scripts for building libpng:
189                            (see scripts/README.txt for the list of scripts)
191Good luck, and happy coding.
193-Glenn Randers-Pehrson (current maintainer, since 1998)
194 Internet: glennrp at
196-Andreas Eric Dilger (former maintainer, 1996-1997)
197 Internet: adilger at
198 Web:
200-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
201 (formerly of Group 42, Inc)
202 Internet: gschal at