src/png/README

   1 README for libpng version 1.6.2 - April 25, 2013 (shared library 16.0)
   2 See the note about version numbers near the top of png.h
   3
   4 See INSTALL for instructions on how to install libpng.
   5
   6 Libpng comes in several distribution formats.  Get libpng-*.tar.gz,
   7 libpng-*.tar.xz or libpng-*.tar.bz2 if you want UNIX-style line endings
   8 in the text files, or lpng*.zip if you want DOS-style line endings.
   9
  10 Version 0.89 was the first official release of libpng.  Don't let the
  11 fact that it's the first release fool you.  The libpng library has been in
  12 extensive use and testing since mid-1995.  By late 1997 it had
  13 finally gotten to the stage where there hadn't been significant
  14 changes to the API in some time, and people have a bad feeling about
  15 libraries with versions < 1.0.  Version 1.0.0 was released in
  16 March 1998.
  17
  18 ****
  19 Note that some of the changes to the png_info structure render this
  20 version of the library binary incompatible with libpng-0.89 or
  21 earlier 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
  23 png_uint_32, which will affect shared-library applications that use
  24 this function.
  25
  26 To avoid problems with changes to the internals of png_info_struct,
  27 new APIs have been made available in 0.95 to avoid direct application
  28 access to info_ptr.  These functions are the png_set_<chunk> and
  29 png_get_<chunk> functions.  These functions should be used when
  30 accessing/storing the info_struct data, rather than manipulating it
  31 directly, to avoid such problems in the future.
  32
  33 It is important to note that the APIs do not make current programs
  34 that access the info struct directly incompatible with the new
  35 library.  However, it is strongly suggested that new programs use
  36 the new APIs (as shown in example.c and pngtest.c), and older programs
  37 be converted to the new format, to facilitate upgrades in the future.
  38 ****
  39
  40 Additions since 0.90 include the ability to compile libpng as a
  41 Windows DLL, and new APIs for accessing data in the info struct.
  42 Experimental functions include the ability to set weighting and cost
  43 factors for row filter selection, direct reads of integers from buffers
  44 on big-endian processors that support misaligned data access, faster
  45 methods of doing alpha composition, and more accurate 16->8 bit color
  46 conversion.
  47
  48 The additions since 0.89 include the ability to read from a PNG stream
  49 which has had some (or all) of the signature bytes read by the calling
  50 application.  This also allows the reading of embedded PNG streams that
  51 do not have the PNG file signature.  As well, it is now possible to set
  52 the library action on the detection of chunk CRC errors.  It is possible
  53 to set different actions based on whether the CRC error occurred in a
  54 critical or an ancillary chunk.
  55
  56 The changes made to the library, and bugs fixed are based on discussions
  57 on the PNG-implement mailing list and not on material submitted
  58 privately to Guy, Andreas, or Glenn.  They will forward any good
  59 suggestions to the list.
  60
  61 For a detailed description on using libpng, read libpng-manual.txt.  For
  62 examples of libpng in a program, see example.c and pngtest.c.  For usage
  63 information and restrictions (what little they are) on libpng, see
  64 png.h.  For a description on using zlib (the compression library used by
  65 libpng) and zlib's restrictions, see zlib.h
  66
  67 I have included a general makefile, as well as several machine and
  68 compiler specific ones, but you may have to modify one for your own needs.
  69
  70 You should use zlib 1.0.4 or later to run this, but it MAY work with
  71 versions as old as zlib 0.95.  Even so, there are bugs in older zlib
  72 versions which can cause the output of invalid compression streams for
  73 some images.  You will definitely need zlib 1.0.4 or later if you are
  74 taking advantage of the MS-DOS "far" structure allocation for the small
  75 and medium memory models.  You should also note that zlib is a
  76 compression library that is useful for more things than just PNG files.
  77 You can use zlib as a drop-in replacement for fread() and fwrite() if
  78 you are so inclined.
  79
  80 zlib should be available at the same place that libpng is, or at.
  81 ftp://ftp.info-zip.org/pub/infozip/zlib
  82
  83 You may also want a copy of the PNG specification.  It is available
  84 as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
  85 these at http://www.libpng.org/pub/png/documents/
  86
  87 This code is currently being archived at libpng.sf.net in the
  88 [DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT)
  89 at GO GRAPHSUP.  If you can't find it in any of those places,
  90 e-mail me, and I'll help you find it.
  91
  92 If you have any code changes, requests, problems, etc., please e-mail
  93 them to me.  Also, I'd appreciate any make files or project files,
  94 and any modifications you needed to make to get libpng to compile,
  95 along with a #define variable to tell what compiler/system you are on.
  96 If you needed to add transformations to libpng, or wish libpng would
  97 provide the image in a different way, drop me a note (and code, if
  98 possible), so I can consider supporting the transformation.
  99 Finally, if you get any warning messages when compiling libpng
 100 (note: not zlib), and they are easy to fix, I'd appreciate the
 101 fix.  Please mention "libpng" somewhere in the subject line.  Thanks.
 102
 103 This release was created and will be supported by myself (of course
 104 based in a large way on Guy's and Andreas' earlier work), and the PNG
 105 development group.
 106
 107 Send comments/corrections/commendations to png-mng-implement at
 108 lists.sourceforge.net (subscription required; visit
 109 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 110 to subscribe) or to glennrp at users.sourceforge.net
 111
 112 You can't reach Guy, the original libpng author, at the addresses
 113 given in previous versions of this document.  He and Andreas will
 114 read mail addressed to the png-implement list, however.
 115
 116 Please do not send general questions about PNG.  Send them to
 117 png-mng-misc at lists.sf.net (subscription required; visit
 118 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
 119 subscribe).  If you have a question about something
 120 in the PNG specification that is related to using libpng, send it
 121 to me.  Send me any questions that start with "I was using libpng,
 122 and ...".  If in doubt, send questions to me.  I'll bounce them
 123 to others, if necessary.
 124
 125 Please do not send suggestions on how to change PNG.  We have
 126 been discussing PNG for sixteen years now, and it is official and
 127 finished.  If you have suggestions for libpng, however, I'll
 128 gladly listen.  Even if your suggestion is not used immediately,
 129 it may be used later.
 130
 131 Files in this distribution:
 132
 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)
 190
 191 Good luck, and happy coding.
 192
 193 -Glenn Randers-Pehrson (current maintainer, since 1998)
 194  Internet: glennrp at users.sourceforge.net
 195
 196 -Andreas Eric Dilger (former maintainer, 1996-1997)
 197  Internet: adilger at enel.ucalgary.ca
 198  Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
 199
 200 -Guy Eric Schalnat (original author and former maintainer, 1995-1996)
 201  (formerly of Group 42, Inc)
 202  Internet: gschal at infinet.com