1README for libpng version 1.6.22rc01 - May 14, 2016 (shared library 16.0)
2See the note about version numbers near the top of png.h
3
4See INSTALL for instructions on how to install libpng.
5
6Libpng comes in several distribution formats.  Get libpng-*.tar.gz or
7libpng-*.tar.xz or if you want UNIX-style line endings in the text files,
8or lpng*.7z or lpng*.zip if you want DOS-style line endings.
9
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.
17
18****
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.
25
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.
32
33It is important to note that the APIs did not make current programs
34that access the info struct directly incompatible with the new
35library, through libpng-1.2.x.  In libpng-1.4.x, which was meant to
36be a transitional release, members of the png_struct and the
37info_struct can still be accessed, but the compiler will issue a
38warning about deprecated usage.  Since libpng-1.5.0, direct access
39to these structs is not allowed, and the definitions of the structs
40reside in private pngstruct.h and pnginfo.h header files that are not
41accessible to applications.  It is strongly suggested that new
42programs use the new APIs (as shown in example.c and pngtest.c), and
43older programs be converted to the new format, to facilitate upgrades
44in the future.
45****
46
47Additions since 0.90 include the ability to compile libpng as a
48Windows DLL, and new APIs for accessing data in the info struct.
49Experimental functions include the ability to set weighting and cost
50factors for row filter selection, direct reads of integers from buffers
51on big-endian processors that support misaligned data access, faster
52methods of doing alpha composition, and more accurate 16->8 bit color
53conversion.
54
55The additions since 0.89 include the ability to read from a PNG stream
56which has had some (or all) of the signature bytes read by the calling
57application.  This also allows the reading of embedded PNG streams that
58do not have the PNG file signature.  As well, it is now possible to set
59the library action on the detection of chunk CRC errors.  It is possible
60to set different actions based on whether the CRC error occurred in a
61critical or an ancillary chunk.
62
63The changes made to the library, and bugs fixed are based on discussions
64on the PNG-implement mailing list and not on material submitted
65privately to Guy, Andreas, or Glenn.  They will forward any good
66suggestions to the list.
67
68For a detailed description on using libpng, read libpng-manual.txt.  For
69examples of libpng in a program, see example.c and pngtest.c.  For usage
70information and restrictions (what little they are) on libpng, see
71png.h.  For a description on using zlib (the compression library used by
72libpng) and zlib's restrictions, see zlib.h
73
74I have included a general makefile, as well as several machine and
75compiler specific ones, but you may have to modify one for your own needs.
76
77You should use zlib 1.0.4 or later to run this, but it MAY work with
78versions as old as zlib 0.95.  Even so, there are bugs in older zlib
79versions which can cause the output of invalid compression streams for
80some images.  You will definitely need zlib 1.0.4 or later if you are
81taking advantage of the MS-DOS "far" structure allocation for the small
82and medium memory models.  You should also note that zlib is a
83compression library that is useful for more things than just PNG files.
84You can use zlib as a drop-in replacement for fread() and fwrite() if
85you are so inclined.
86
87zlib should be available at the same place that libpng is, or at zlib.net.
88
89You may also want a copy of the PNG specification.  It is available
90as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
91these at http://www.libpng.org/pub/png/documents/
92
93This code is currently being archived at libpng.sf.net in the
94[DOWNLOAD] area, and at ftp://ftp.simplesystems.org.  If you can't find it
95in any of those places, e-mail me, and I'll help you find it.
96
97I am not a lawyer, but I believe that the Export Control Classification
98Number (ECCN) for libpng is EAR99, which means not subject to export
99controls or International Traffic in Arms Regulations (ITAR) because it
100is open source, publicly available software, that does not contain any
101encryption software.  See the EAR, paragraphs 734.3(b)(3) and 734.7(b).
102
103If you have any code changes, requests, problems, etc., please e-mail
104them to me.  Also, I'd appreciate any make files or project files,
105and any modifications you needed to make to get libpng to compile,
106along with a #define variable to tell what compiler/system you are on.
107If you needed to add transformations to libpng, or wish libpng would
108provide the image in a different way, drop me a note (and code, if
109possible), so I can consider supporting the transformation.
110Finally, if you get any warning messages when compiling libpng
111(note: not zlib), and they are easy to fix, I'd appreciate the
112fix.  Please mention "libpng" somewhere in the subject line.  Thanks.
113
114This release was created and will be supported by myself (of course
115based in a large way on Guy's and Andreas' earlier work), and the PNG
116development group.
117
118Send comments/corrections/commendations to png-mng-implement at
119lists.sourceforge.net (subscription required; visit
120https://lists.sourceforge.net/lists/listinfo/png-mng-implement
121to subscribe) or to glennrp at users.sourceforge.net
122
123You can't reach Guy, the original libpng author, at the addresses
124given in previous versions of this document.  He and Andreas will
125read mail addressed to the png-implement list, however.
126
127Please do not send general questions about PNG.  Send them to
128png-mng-misc at lists.sf.net (subscription required; visit
129https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
130subscribe).  If you have a question about something
131in the PNG specification that is related to using libpng, send it
132to me.  Send me any questions that start with "I was using libpng,
133and ...".  If in doubt, send questions to me.  I'll bounce them
134to others, if necessary.
135
136Please do not send suggestions on how to change PNG.  We have
137been discussing PNG for twenty years now, and it is official and
138finished.  If you have suggestions for libpng, however, I'll
139gladly listen.  Even if your suggestion is not used immediately,
140it may be used later.
141
142Files in this distribution:
143
144      ANNOUNCE      =>  Announcement of this version, with recent changes
145      CHANGES       =>  Description of changes between libpng versions
146      KNOWNBUG      =>  List of known bugs and deficiencies
147      LICENSE       =>  License to use and redistribute libpng
148      README        =>  This file
149      TODO          =>  Things not implemented in the current library
150      Y2KINFO       =>  Statement of Y2K compliance
151      example.c     =>  Example code for using libpng functions
152      libpng.3      =>  manual page for libpng (includes libpng-manual.txt)
153      libpng-manual.txt  =>  Description of libpng and its functions
154      libpngpf.3    =>  manual page for libpng's private functions
155      png.5         =>  manual page for the PNG format
156      png.c         =>  Basic interface functions common to library
157      png.h         =>  Library function and interface declarations (public)
158      pngpriv.h     =>  Library function and interface declarations (private)
159      pngconf.h     =>  System specific library configuration (public)
160      pngstruct.h   =>  png_struct declaration (private)
161      pnginfo.h     =>  png_info struct declaration (private)
162      pngdebug.h    =>  debugging macros (private)
163      pngerror.c    =>  Error/warning message I/O functions
164      pngget.c      =>  Functions for retrieving info from struct
165      pngmem.c      =>  Memory handling functions
166      pngbar.png    =>  PNG logo, 88x31
167      pngnow.png    =>  PNG logo, 98x31
168      pngpread.c    =>  Progressive reading functions
169      pngread.c     =>  Read data/helper high-level functions
170      pngrio.c      =>  Lowest-level data read I/O functions
171      pngrtran.c    =>  Read data transformation functions
172      pngrutil.c    =>  Read data utility functions
173      pngset.c      =>  Functions for storing data into the info_struct
174      pngtest.c     =>  Library test program
175      pngtest.png   =>  Library test sample image
176      pngtrans.c    =>  Common data transformation functions
177      pngwio.c      =>  Lowest-level write I/O functions
178      pngwrite.c    =>  High-level write functions
179      pngwtran.c    =>  Write data transformations
180      pngwutil.c    =>  Write utility functions
181      arm           =>  Contains optimized code for the ARM platform
182      contrib       =>  Contributions
183       examples         =>  Example programs
184       gregbook         =>  source code for PNG reading and writing, from
185                            Greg Roelofs' "PNG: The Definitive Guide",
186                            O'Reilly, 1999
187       libtests         =>  Test programs
188       pngminim         =>  Minimal decoder, encoder, and progressive decoder
189                            programs demonstrating use of pngusr.dfa
190       pngminus         =>  Simple pnm2png and png2pnm programs
191       pngsuite         =>  Test images
192       tools            =>  Various tools
193       visupng          =>  Contains a MSVC workspace for VisualPng
194      projects      =>  Contains project files and workspaces for
195                        building a DLL
196       owatcom          =>  Contains a WATCOM project for building libpng
197       visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
198                            workspace for building libpng and zlib
199       vstudio          =>  Contains a Microsoft Visual C++ (MSVC)
200                            workspace for building libpng and zlib
201      scripts       =>  Directory containing scripts for building libpng:
202                            (see scripts/README.txt for the list of scripts)
203
204Good luck, and happy coding.
205
206-Glenn Randers-Pehrson (current maintainer, since 1998)
207 Internet: glennrp at users.sourceforge.net
208
209-Andreas Eric Dilger (former maintainer, 1996-1997)
210 Internet: adilger at enel.ucalgary.ca
211 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
212
213-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
214 (formerly of Group 42, Inc)
215 Internet: gschal at infinet.com
216