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1 libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project | 1 libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project |
2 to include only information relevant to libjpeg-turbo, to wordsmith certain | 2 to include only information relevant to libjpeg-turbo, to wordsmith certain |
3 sections, and to remove impolitic language that existed in the libjpeg v8 | 3 sections, and to remove impolitic language that existed in the libjpeg v8 |
4 README. It is included only for reference. Please see README-turbo.txt for | 4 README. It is included only for reference. Please see README.md for |
5 information specific to libjpeg-turbo. | 5 information specific to libjpeg-turbo. |
6 | 6 |
7 | 7 |
8 The Independent JPEG Group's JPEG software | 8 The Independent JPEG Group's JPEG software |
9 ========================================== | 9 ========================================== |
10 | 10 |
11 This distribution contains a release of the Independent JPEG Group's free JPEG | 11 This distribution contains a release of the Independent JPEG Group's free JPEG |
12 software. You are welcome to redistribute this software and to use it for any | 12 software. You are welcome to redistribute this software and to use it for any |
13 purpose, subject to the conditions under LEGAL ISSUES, below. | 13 purpose, subject to the conditions under LEGAL ISSUES, below. |
14 | 14 |
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29 OVERVIEW General description of JPEG and the IJG software. | 29 OVERVIEW General description of JPEG and the IJG software. |
30 LEGAL ISSUES Copyright, lack of warranty, terms of distribution. | 30 LEGAL ISSUES Copyright, lack of warranty, terms of distribution. |
31 REFERENCES Where to learn more about JPEG. | 31 REFERENCES Where to learn more about JPEG. |
32 ARCHIVE LOCATIONS Where to find newer versions of this software. | 32 ARCHIVE LOCATIONS Where to find newer versions of this software. |
33 FILE FORMAT WARS Software *not* to get. | 33 FILE FORMAT WARS Software *not* to get. |
34 TO DO Plans for future IJG releases. | 34 TO DO Plans for future IJG releases. |
35 | 35 |
36 Other documentation files in the distribution are: | 36 Other documentation files in the distribution are: |
37 | 37 |
38 User documentation: | 38 User documentation: |
39 install.txt How to configure and install the IJG software. | |
40 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, | 39 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, |
41 rdjpgcom, and wrjpgcom. | 40 rdjpgcom, and wrjpgcom. |
42 *.1 Unix-style man pages for programs (same info as usage.txt). | 41 *.1 Unix-style man pages for programs (same info as usage.txt). |
43 wizard.txt Advanced usage instructions for JPEG wizards only. | 42 wizard.txt Advanced usage instructions for JPEG wizards only. |
44 change.log Version-to-version change highlights. | 43 change.log Version-to-version change highlights. |
45 Programmer and internal documentation: | 44 Programmer and internal documentation: |
46 libjpeg.txt How to use the JPEG library in your own programs. | 45 libjpeg.txt How to use the JPEG library in your own programs. |
47 example.c Sample code for calling the JPEG library. | 46 example.c Sample code for calling the JPEG library. |
48 structure.txt Overview of the JPEG library's internal structure. | 47 structure.txt Overview of the JPEG library's internal structure. |
49 coderules.txt Coding style rules --- please read if you contribute code. | 48 coderules.txt Coding style rules --- please read if you contribute code. |
50 | 49 |
51 Please read at least the files install.txt and usage.txt. Some information | 50 Please read at least usage.txt. Some information can also be found in the JPEG |
52 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See | 51 FAQ (Frequently Asked Questions) article. See ARCHIVE LOCATIONS below to find |
53 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. | 52 out where to obtain the FAQ article. |
54 | 53 |
55 If you want to understand how the JPEG code works, we suggest reading one or | 54 If you want to understand how the JPEG code works, we suggest reading one or |
56 more of the REFERENCES, then looking at the documentation files (in roughly | 55 more of the REFERENCES, then looking at the documentation files (in roughly |
57 the order listed) before diving into the code. | 56 the order listed) before diving into the code. |
58 | 57 |
59 | 58 |
60 OVERVIEW | 59 OVERVIEW |
61 ======== | 60 ======== |
62 | 61 |
63 This package contains C software to implement JPEG image encoding, decoding, | 62 This package contains C software to implement JPEG image encoding, decoding, |
64 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression | 63 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression |
65 method for full-color and gray-scale images. JPEG's strong suit is compressing | 64 method for full-color and grayscale images. JPEG's strong suit is compressing |
66 photographic images or other types of images that have smooth color and | 65 photographic images or other types of images that have smooth color and |
67 brightness transitions between neighboring pixels. Images with sharp lines or | 66 brightness transitions between neighboring pixels. Images with sharp lines or |
68 other abrupt features may not compress well with JPEG, and a higher JPEG | 67 other abrupt features may not compress well with JPEG, and a higher JPEG |
69 quality may have to be used to avoid visible compression artifacts with such | 68 quality may have to be used to avoid visible compression artifacts with such |
70 images. | 69 images. |
71 | 70 |
72 JPEG is lossy, meaning that the output pixels are not necessarily identical to | 71 JPEG is lossy, meaning that the output pixels are not necessarily identical to |
73 the input pixels. However, on photographic content and other "smooth" images, | 72 the input pixels. However, on photographic content and other "smooth" images, |
74 very good compression ratios can be obtained with no visible compression | 73 very good compression ratios can be obtained with no visible compression |
75 artifacts, and extremely high compression ratios are possible if you are | 74 artifacts, and extremely high compression ratios are possible if you are |
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122 program, you must acknowledge somewhere in your documentation that | 121 program, you must acknowledge somewhere in your documentation that |
123 you've used the IJG code. | 122 you've used the IJG code. |
124 | 123 |
125 In legalese: | 124 In legalese: |
126 | 125 |
127 The authors make NO WARRANTY or representation, either express or implied, | 126 The authors make NO WARRANTY or representation, either express or implied, |
128 with respect to this software, its quality, accuracy, merchantability, or | 127 with respect to this software, its quality, accuracy, merchantability, or |
129 fitness for a particular purpose. This software is provided "AS IS", and you, | 128 fitness for a particular purpose. This software is provided "AS IS", and you, |
130 its user, assume the entire risk as to its quality and accuracy. | 129 its user, assume the entire risk as to its quality and accuracy. |
131 | 130 |
132 This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding. | 131 This software is copyright (C) 1991-2016, Thomas G. Lane, Guido Vollbeding. |
133 All Rights Reserved except as specified below. | 132 All Rights Reserved except as specified below. |
134 | 133 |
135 Permission is hereby granted to use, copy, modify, and distribute this | 134 Permission is hereby granted to use, copy, modify, and distribute this |
136 software (or portions thereof) for any purpose, without fee, subject to these | 135 software (or portions thereof) for any purpose, without fee, subject to these |
137 conditions: | 136 conditions: |
138 (1) If any part of the source code for this software is distributed, then this | 137 (1) If any part of the source code for this software is distributed, then this |
139 README file must be included, with this copyright and no-warranty notice | 138 README file must be included, with this copyright and no-warranty notice |
140 unaltered; and any additions, deletions, or changes to the original files | 139 unaltered; and any additions, deletions, or changes to the original files |
141 must be clearly indicated in accompanying documentation. | 140 must be clearly indicated in accompanying documentation. |
142 (2) If only executable code is distributed, then the accompanying | 141 (2) If only executable code is distributed, then the accompanying |
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160 assumed by the product vendor. | 159 assumed by the product vendor. |
161 | 160 |
162 | 161 |
163 The Unix configuration script "configure" was produced with GNU Autoconf. | 162 The Unix configuration script "configure" was produced with GNU Autoconf. |
164 It is copyright by the Free Software Foundation but is freely distributable. | 163 It is copyright by the Free Software Foundation but is freely distributable. |
165 The same holds for its supporting scripts (config.guess, config.sub, | 164 The same holds for its supporting scripts (config.guess, config.sub, |
166 ltmain.sh). Another support script, install-sh, is copyright by X Consortium | 165 ltmain.sh). Another support script, install-sh, is copyright by X Consortium |
167 but is also freely distributable. | 166 but is also freely distributable. |
168 | 167 |
169 The IJG distribution formerly included code to read and write GIF files. | 168 The IJG distribution formerly included code to read and write GIF files. |
170 To avoid entanglement with the Unisys LZW patent, GIF reading support has | 169 To avoid entanglement with the Unisys LZW patent (now expired), GIF reading |
171 been removed altogether, and the GIF writer has been simplified to produce | 170 support has been removed altogether, and the GIF writer has been simplified |
172 "uncompressed GIFs". This technique does not use the LZW algorithm; the | 171 to produce "uncompressed GIFs". This technique does not use the LZW |
173 resulting GIF files are larger than usual, but are readable by all standard | 172 algorithm; the resulting GIF files are larger than usual, but are readable |
174 GIF decoders. | 173 by all standard GIF decoders. |
175 | 174 |
176 We are required to state that | 175 We are required to state that |
177 "The Graphics Interchange Format(c) is the Copyright property of | 176 "The Graphics Interchange Format(c) is the Copyright property of |
178 CompuServe Incorporated. GIF(sm) is a Service Mark property of | 177 CompuServe Incorporated. GIF(sm) is a Service Mark property of |
179 CompuServe Incorporated." | 178 CompuServe Incorporated." |
180 | 179 |
181 | 180 |
182 REFERENCES | 181 REFERENCES |
183 ========== | 182 ========== |
184 | 183 |
185 We recommend reading one or more of these references before trying to | 184 We recommend reading one or more of these references before trying to |
186 understand the innards of the JPEG software. | 185 understand the innards of the JPEG software. |
187 | 186 |
188 The best short technical introduction to the JPEG compression algorithm is | 187 The best short technical introduction to the JPEG compression algorithm is |
189 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", | 188 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", |
190 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. | 189 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. |
191 (Adjacent articles in that issue discuss MPEG motion picture compression, | 190 (Adjacent articles in that issue discuss MPEG motion picture compression, |
192 applications of JPEG, and related topics.) If you don't have the CACM issue | 191 applications of JPEG, and related topics.) If you don't have the CACM issue |
193 handy, a PostScript file containing a revised version of Wallace's article is | 192 handy, a PDF file containing a revised version of Wallace's article is |
194 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually | 193 available at http://www.ijg.org/files/Wallace.JPEG.pdf. The file (actually |
195 a preprint for an article that appeared in IEEE Trans. Consumer Electronics) | 194 a preprint for an article that appeared in IEEE Trans. Consumer Electronics) |
196 omits the sample images that appeared in CACM, but it includes corrections | 195 omits the sample images that appeared in CACM, but it includes corrections |
197 and some added material. Note: the Wallace article is copyright ACM and IEEE, | 196 and some added material. Note: the Wallace article is copyright ACM and IEEE, |
198 and it may not be used for commercial purposes. | 197 and it may not be used for commercial purposes. |
199 | 198 |
200 A somewhat less technical, more leisurely introduction to JPEG can be found in | 199 A somewhat less technical, more leisurely introduction to JPEG can be found in |
201 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by | 200 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by |
202 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides | 201 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides |
203 good explanations and example C code for a multitude of compression methods | 202 good explanations and example C code for a multitude of compression methods |
204 including JPEG. It is an excellent source if you are comfortable reading C | 203 including JPEG. It is an excellent source if you are comfortable reading C |
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240 of the TIFF spec will replace the 6.0 JPEG design with the Note's design. | 239 of the TIFF spec will replace the 6.0 JPEG design with the Note's design. |
241 Although IJG's own code does not support TIFF/JPEG, the free libtiff library | 240 Although IJG's own code does not support TIFF/JPEG, the free libtiff library |
242 uses our library to implement TIFF/JPEG per the Note. | 241 uses our library to implement TIFF/JPEG per the Note. |
243 | 242 |
244 | 243 |
245 ARCHIVE LOCATIONS | 244 ARCHIVE LOCATIONS |
246 ================= | 245 ================= |
247 | 246 |
248 The "official" archive site for this software is www.ijg.org. | 247 The "official" archive site for this software is www.ijg.org. |
249 The most recent released version can always be found there in | 248 The most recent released version can always be found there in |
250 directory "files". This particular version will be archived as | 249 directory "files". |
251 http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible | |
252 "zip" archive format as http://www.ijg.org/files/jpegsr8d.zip. | |
253 | 250 |
254 The JPEG FAQ (Frequently Asked Questions) article is a source of some | 251 The JPEG FAQ (Frequently Asked Questions) article is a source of some |
255 general information about JPEG. | 252 general information about JPEG. |
256 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ | 253 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ |
257 and other news.answers archive sites, including the official news.answers | 254 and other news.answers archive sites, including the official news.answers |
258 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. | 255 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. |
259 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu | 256 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu |
260 with body | 257 with body |
261 send usenet/news.answers/jpeg-faq/part1 | 258 send usenet/news.answers/jpeg-faq/part1 |
262 send usenet/news.answers/jpeg-faq/part2 | 259 send usenet/news.answers/jpeg-faq/part2 |
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273 common, interoperable format standards for JPEG files. | 270 common, interoperable format standards for JPEG files. |
274 Don't use an incompatible file format! | 271 Don't use an incompatible file format! |
275 (In any case, our decoder will remain capable of reading existing JPEG | 272 (In any case, our decoder will remain capable of reading existing JPEG |
276 image files indefinitely.) | 273 image files indefinitely.) |
277 | 274 |
278 | 275 |
279 TO DO | 276 TO DO |
280 ===== | 277 ===== |
281 | 278 |
282 Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. | 279 Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. |
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