|
1 README for libpng version 1.6.28 - January 5, 2017 (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 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. |
|
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 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 **** |
|
46 |
|
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. |
|
54 |
|
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. |
|
62 |
|
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. |
|
67 |
|
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 |
|
73 |
|
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. |
|
76 |
|
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. |
|
86 |
|
87 zlib should be available at the same place that libpng is, or at zlib.net. |
|
88 |
|
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/ |
|
92 |
|
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. |
|
96 |
|
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). |
|
102 |
|
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. |
|
113 |
|
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. |
|
117 |
|
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 |
|
122 |
|
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. |
|
126 |
|
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. |
|
135 |
|
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. |
|
141 |
|
142 Files 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 arm-neon => Optimized code for ARM-NEON platform |
|
184 examples => Example programs |
|
185 gregbook => source code for PNG reading and writing, from |
|
186 Greg Roelofs' "PNG: The Definitive Guide", |
|
187 O'Reilly, 1999 |
|
188 intel => Optimized code for INTEL-SSE2 platform |
|
189 libtests => Test programs |
|
190 pngminim => Minimal decoder, encoder, and progressive decoder |
|
191 programs demonstrating use of pngusr.dfa |
|
192 pngminus => Simple pnm2png and png2pnm programs |
|
193 pngsuite => Test images |
|
194 testpngs |
|
195 tools => Various tools |
|
196 visupng => Contains a MSVC workspace for VisualPng |
|
197 projects => Contains project files and workspaces for |
|
198 building a DLL |
|
199 owatcom => Contains a WATCOM project for building libpng |
|
200 visualc71 => Contains a Microsoft Visual C++ (MSVC) |
|
201 workspace for building libpng and zlib |
|
202 vstudio => Contains a Microsoft Visual C++ (MSVC) |
|
203 workspace for building libpng and zlib |
|
204 scripts => Directory containing scripts for building libpng: |
|
205 (see scripts/README.txt for the list of scripts) |
|
206 |
|
207 Good luck, and happy coding. |
|
208 |
|
209 -Glenn Randers-Pehrson (current maintainer, since 1998) |
|
210 Internet: glennrp at users.sourceforge.net |
|
211 |
|
212 -Andreas Eric Dilger (former maintainer, 1996-1997) |
|
213 Internet: adilger at enel.ucalgary.ca |
|
214 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/ |
|
215 |
|
216 -Guy Eric Schalnat (original author and former maintainer, 1995-1996) |
|
217 (formerly of Group 42, Inc) |
|
218 Internet: gschal at infinet.com |