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1 README for libpng version 1.6.21 - January 15, 2016 (shared library 16.0)
2 See the note about version numbers near the top of png.h
4 See INSTALL for instructions on how to install libpng.
6 Libpng comes in several distribution formats. Get libpng-*.tar.gz or
7 libpng-*.tar.xz or if you want UNIX-style line endings in the text files,
8 or lpng*.7z or lpng*.zip if you want DOS-style line endings.
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.
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.
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.
33 It is important to note that the APIs did not make current programs
34 that access the info struct directly incompatible with the new
35 library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
36 be a transitional release, members of the png_struct and the
37 info_struct can still be accessed, but the compiler will issue a
38 warning about deprecated usage. Since libpng-1.5.0, direct access
39 to these structs is not allowed, and the definitions of the structs
40 reside in private pngstruct.h and pnginfo.h header files that are not
41 accessible to applications. It is strongly suggested that new
42 programs use the new APIs (as shown in example.c and pngtest.c), and
43 older programs be converted to the new format, to facilitate upgrades
44 in the future.
45 ****
47 Additions since 0.90 include the ability to compile libpng as a
48 Windows DLL, and new APIs for accessing data in the info struct.
49 Experimental functions include the ability to set weighting and cost
50 factors for row filter selection, direct reads of integers from buffers
51 on big-endian processors that support misaligned data access, faster
52 methods of doing alpha composition, and more accurate 16->8 bit color
53 conversion.
55 The additions since 0.89 include the ability to read from a PNG stream
56 which has had some (or all) of the signature bytes read by the calling
57 application. This also allows the reading of embedded PNG streams that
58 do not have the PNG file signature. As well, it is now possible to set
59 the library action on the detection of chunk CRC errors. It is possible
60 to set different actions based on whether the CRC error occurred in a
61 critical or an ancillary chunk.
63 The changes made to the library, and bugs fixed are based on discussions
64 on the PNG-implement mailing list and not on material submitted
65 privately to Guy, Andreas, or Glenn. They will forward any good
66 suggestions to the list.
68 For a detailed description on using libpng, read libpng-manual.txt. For
69 examples of libpng in a program, see example.c and pngtest.c. For usage
70 information and restrictions (what little they are) on libpng, see
71 png.h. For a description on using zlib (the compression library used by
72 libpng) and zlib's restrictions, see zlib.h
74 I have included a general makefile, as well as several machine and
75 compiler specific ones, but you may have to modify one for your own needs.
77 You should use zlib 1.0.4 or later to run this, but it MAY work with
78 versions as old as zlib 0.95. Even so, there are bugs in older zlib
79 versions which can cause the output of invalid compression streams for
80 some images. You will definitely need zlib 1.0.4 or later if you are
81 taking advantage of the MS-DOS "far" structure allocation for the small
82 and medium memory models. You should also note that zlib is a
83 compression library that is useful for more things than just PNG files.
84 You can use zlib as a drop-in replacement for fread() and fwrite() if
85 you are so inclined.
87 zlib should be available at the same place that libpng is, or at zlib.net.
89 You may also want a copy of the PNG specification. It is available
90 as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
91 these at http://www.libpng.org/pub/png/documents/
93 This 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
95 in any of those places, e-mail me, and I'll help you find it.
97 I am not a lawyer, but I believe that the Export Control Classification
98 Number (ECCN) for libpng is EAR99, which means not subject to export
99 controls or International Traffic in Arms Regulations (ITAR) because it
100 is open source, publicly available software, that does not contain any
101 encryption software. See the EAR, paragraphs 734.3(b)(3) and 734.7(b).
103 If you have any code changes, requests, problems, etc., please e-mail
104 them to me. Also, I'd appreciate any make files or project files,
105 and any modifications you needed to make to get libpng to compile,
106 along with a #define variable to tell what compiler/system you are on.
107 If you needed to add transformations to libpng, or wish libpng would
108 provide the image in a different way, drop me a note (and code, if
109 possible), so I can consider supporting the transformation.
110 Finally, if you get any warning messages when compiling libpng
111 (note: not zlib), and they are easy to fix, I'd appreciate the
112 fix. Please mention "libpng" somewhere in the subject line. Thanks.
114 This release was created and will be supported by myself (of course
115 based in a large way on Guy's and Andreas' earlier work), and the PNG
116 development group.
118 Send comments/corrections/commendations to png-mng-implement at
119 lists.sourceforge.net (subscription required; visit
120 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
121 to subscribe) or to glennrp at users.sourceforge.net
123 You can't reach Guy, the original libpng author, at the addresses
124 given in previous versions of this document. He and Andreas will
125 read mail addressed to the png-implement list, however.
127 Please do not send general questions about PNG. Send them to
128 png-mng-misc at lists.sf.net (subscription required; visit
129 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
130 subscribe). If you have a question about something
131 in the PNG specification that is related to using libpng, send it
132 to me. Send me any questions that start with "I was using libpng,
133 and ...". If in doubt, send questions to me. I'll bounce them
134 to others, if necessary.
136 Please do not send suggestions on how to change PNG. We have
137 been discussing PNG for twenty years now, and it is official and
138 finished. If you have suggestions for libpng, however, I'll
139 gladly listen. Even if your suggestion is not used immediately,
140 it may be used later.
142 Files in this distribution:
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)
204 Good luck, and happy coding.
206 -Glenn Randers-Pehrson (current maintainer, since 1998)
207 Internet: glennrp at users.sourceforge.net
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/
213 -Guy Eric Schalnat (original author and former maintainer, 1995-1996)
214 (formerly of Group 42, Inc)
215 Internet: gschal at infinet.com