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LICENSE.md | D | 12-May-2024 | 5.1 KiB | 133 | 96 | |
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README.OpenSource | D | 12-May-2024 | 290 | 11 | 11 | |
README.ijg | D | 12-May-2024 | 13.4 KiB | 278 | 220 | |
README.md | D | 12-May-2024 | 16.6 KiB | 357 | 278 | |
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cderror.h | D | 12-May-2024 | 5.4 KiB | 138 | 98 | |
cdjpeg.c | D | 12-May-2024 | 3.9 KiB | 146 | 94 | |
cdjpeg.h | D | 12-May-2024 | 5.6 KiB | 158 | 79 | |
change.log | D | 12-May-2024 | 12.1 KiB | 316 | 219 | |
cjpeg.1 | D | 12-May-2024 | 13.3 KiB | 355 | 354 | |
cjpeg.c | D | 12-May-2024 | 22.9 KiB | 694 | 459 | |
cmyk.h | D | 12-May-2024 | 1.6 KiB | 62 | 36 | |
coderules.txt | D | 12-May-2024 | 3.4 KiB | 79 | 60 | |
djpeg.1 | D | 12-May-2024 | 9.7 KiB | 297 | 296 | |
djpeg.c | D | 12-May-2024 | 27.1 KiB | 823 | 566 | |
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jaricom.c | D | 12-May-2024 | 5 KiB | 158 | 121 | |
jcapimin.c | D | 12-May-2024 | 9.5 KiB | 296 | 142 | |
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jccoefct.c | D | 12-May-2024 | 16.9 KiB | 450 | 279 | |
jccolext.c | D | 12-May-2024 | 4.5 KiB | 145 | 84 | |
jccolor.c | D | 12-May-2024 | 23.2 KiB | 711 | 535 | |
jcdctmgr.c | D | 12-May-2024 | 22 KiB | 722 | 461 | |
jchuff.c | D | 12-May-2024 | 33.7 KiB | 1,097 | 652 | |
jchuff.h | D | 12-May-2024 | 1.5 KiB | 43 | 13 | |
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jcinit.c | D | 12-May-2024 | 2.4 KiB | 78 | 36 | |
jcmainct.c | D | 12-May-2024 | 5.1 KiB | 163 | 83 | |
jcmarker.c | D | 12-May-2024 | 17.1 KiB | 665 | 393 | |
jcmaster.c | D | 12-May-2024 | 21.4 KiB | 641 | 418 | |
jcomapi.c | D | 12-May-2024 | 3.2 KiB | 110 | 45 | |
jconfig.h | D | 12-May-2024 | 2.8 KiB | 92 | 17 | |
jconfig.h.in | D | 12-May-2024 | 2.2 KiB | 74 | 53 | |
jconfig.txt | D | 12-May-2024 | 4.8 KiB | 144 | 115 | |
jconfigint.h | D | 12-May-2024 | 1.7 KiB | 64 | 28 | |
jconfigint.h.in | D | 12-May-2024 | 875 | 35 | 25 | |
jcparam.c | D | 12-May-2024 | 17.8 KiB | 542 | 323 | |
jcphuff.c | D | 12-May-2024 | 32.5 KiB | 1,106 | 725 | |
jcprepct.c | D | 12-May-2024 | 12.7 KiB | 352 | 208 | |
jcsample.c | D | 12-May-2024 | 19.7 KiB | 540 | 313 | |
jcstest.c | D | 12-May-2024 | 3.8 KiB | 127 | 77 | |
jctrans.c | D | 12-May-2024 | 14.6 KiB | 401 | 226 | |
jdapimin.c | D | 12-May-2024 | 12.9 KiB | 408 | 228 | |
jdapistd.c | D | 12-May-2024 | 25.4 KiB | 696 | 405 | |
jdarith.c | D | 12-May-2024 | 24.6 KiB | 774 | 489 | |
jdatadst-tj.c | D | 12-May-2024 | 6.7 KiB | 203 | 92 | |
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jdatasrc-tj.c | D | 12-May-2024 | 6.8 KiB | 195 | 60 | |
jdatasrc.c | D | 12-May-2024 | 10 KiB | 296 | 122 | |
jdcoefct.c | D | 12-May-2024 | 24.8 KiB | 693 | 485 | |
jdcoefct.h | D | 12-May-2024 | 2.6 KiB | 83 | 36 | |
jdcol565.c | D | 12-May-2024 | 12 KiB | 385 | 333 | |
jdcolext.c | D | 12-May-2024 | 4.4 KiB | 144 | 88 | |
jdcolor.c | D | 12-May-2024 | 28.1 KiB | 884 | 652 | |
jdct.h | D | 12-May-2024 | 9.5 KiB | 209 | 101 | |
jddctmgr.c | D | 12-May-2024 | 11.1 KiB | 353 | 247 | |
jdhuff.c | D | 12-May-2024 | 25.7 KiB | 832 | 477 | |
jdhuff.h | D | 12-May-2024 | 9.3 KiB | 239 | 107 | |
jdicc.c | D | 12-May-2024 | 5.6 KiB | 172 | 106 | |
jdinput.c | D | 12-May-2024 | 14.2 KiB | 409 | 228 | |
jdmainct.c | D | 12-May-2024 | 19.3 KiB | 461 | 226 | |
jdmainct.h | D | 12-May-2024 | 2.4 KiB | 72 | 40 | |
jdmarker.c | D | 12-May-2024 | 41.7 KiB | 1,378 | 865 | |
jdmaster.c | D | 12-May-2024 | 27.3 KiB | 738 | 477 | |
jdmaster.h | D | 12-May-2024 | 788 | 29 | 8 | |
jdmerge.c | D | 12-May-2024 | 19.4 KiB | 590 | 416 | |
jdmerge.h | D | 12-May-2024 | 1.6 KiB | 47 | 18 | |
jdmrg565.c | D | 12-May-2024 | 11.2 KiB | 355 | 279 | |
jdmrgext.c | D | 12-May-2024 | 5.9 KiB | 185 | 145 | |
jdphuff.c | D | 12-May-2024 | 21.8 KiB | 688 | 401 | |
jdpostct.c | D | 12-May-2024 | 10.7 KiB | 295 | 182 | |
jdsample.c | D | 12-May-2024 | 17.7 KiB | 519 | 320 | |
jdsample.h | D | 12-May-2024 | 1.7 KiB | 51 | 17 | |
jdtrans.c | D | 12-May-2024 | 5.3 KiB | 156 | 78 | |
jerror.c | D | 12-May-2024 | 7.7 KiB | 252 | 108 | |
jerror.h | D | 12-May-2024 | 14.8 KiB | 317 | 265 | |
jfdctflt.c | D | 12-May-2024 | 5.5 KiB | 170 | 86 | |
jfdctfst.c | D | 12-May-2024 | 7.6 KiB | 228 | 104 | |
jfdctint.c | D | 12-May-2024 | 11.2 KiB | 289 | 148 | |
jidctflt.c | D | 12-May-2024 | 8.5 KiB | 241 | 124 | |
jidctfst.c | D | 12-May-2024 | 13.2 KiB | 372 | 197 | |
jidctint.c | D | 12-May-2024 | 103.7 KiB | 2,628 | 1,848 | |
jidctred.c | D | 12-May-2024 | 14.2 KiB | 410 | 245 | |
jinclude.h | D | 12-May-2024 | 2.9 KiB | 89 | 29 | |
jmemmgr.c | D | 12-May-2024 | 43.7 KiB | 1,180 | 687 | |
jmemnobs.c | D | 12-May-2024 | 2.8 KiB | 116 | 56 | |
jmemsys.h | D | 12-May-2024 | 7.6 KiB | 179 | 53 | |
jmorecfg.h | D | 12-May-2024 | 14.9 KiB | 424 | 164 | |
jpeg_nbits_table.h | D | 12-May-2024 | 264.1 KiB | 4,099 | 4,098 | |
jpegcomp.h | D | 12-May-2024 | 1.1 KiB | 32 | 19 | |
jpegint.h | D | 12-May-2024 | 15.2 KiB | 369 | 232 | |
jpeglib.h | D | 12-May-2024 | 49.1 KiB | 1,133 | 533 | |
jpegtran.1 | D | 12-May-2024 | 9.6 KiB | 296 | 294 | |
jpegtran.c | D | 12-May-2024 | 19.8 KiB | 601 | 413 | |
jquant1.c | D | 12-May-2024 | 31.7 KiB | 860 | 488 | |
jquant2.c | D | 12-May-2024 | 47.8 KiB | 1,286 | 747 | |
jsimd.h | D | 12-May-2024 | 5.4 KiB | 118 | 85 | |
jsimd_none.c | D | 12-May-2024 | 7.6 KiB | 419 | 340 | |
jsimddct.h | D | 12-May-2024 | 3 KiB | 71 | 50 | |
jstdhuff.c | D | 12-May-2024 | 5.2 KiB | 144 | 103 | |
jutils.c | D | 12-May-2024 | 3.7 KiB | 134 | 65 | |
jversion.h | D | 12-May-2024 | 1.6 KiB | 53 | 21 | |
libjpeg.map.in | D | 12-May-2024 | 164 | 12 | 10 | |
libjpeg.txt | D | 12-May-2024 | 165.9 KiB | 3,145 | 2,620 | |
rdbmp.c | D | 12-May-2024 | 22.4 KiB | 690 | 506 | |
rdcolmap.c | D | 12-May-2024 | 6.9 KiB | 255 | 143 | |
rdgif.c | D | 12-May-2024 | 1.3 KiB | 40 | 10 | |
rdjpgcom.1 | D | 12-May-2024 | 1.7 KiB | 64 | 63 | |
rdjpgcom.c | D | 12-May-2024 | 14.6 KiB | 511 | 317 | |
rdppm.c | D | 12-May-2024 | 24.6 KiB | 781 | 586 | |
rdrle.c | D | 12-May-2024 | 11.4 KiB | 390 | 235 | |
rdswitch.c | D | 12-May-2024 | 12.8 KiB | 425 | 301 | |
rdtarga.c | D | 12-May-2024 | 15.1 KiB | 510 | 324 | |
structure.txt | D | 12-May-2024 | 48.6 KiB | 905 | 739 | |
tjbench.c | D | 12-May-2024 | 38.2 KiB | 1,028 | 892 | |
tjbenchtest.in | D | 12-May-2024 | 11.7 KiB | 257 | 211 | |
tjbenchtest.java.in | D | 12-May-2024 | 10.1 KiB | 216 | 170 | |
tjexample.c | D | 12-May-2024 | 14.8 KiB | 397 | 290 | |
tjexampletest.in | D | 12-May-2024 | 8 KiB | 150 | 126 | |
tjexampletest.java.in | D | 12-May-2024 | 8.2 KiB | 152 | 128 | |
tjunittest.c | D | 12-May-2024 | 29.5 KiB | 932 | 779 | |
tjutil.c | D | 12-May-2024 | 2.2 KiB | 71 | 31 | |
tjutil.h | D | 12-May-2024 | 1.9 KiB | 48 | 16 | |
transupp.c | D | 12-May-2024 | 61.2 KiB | 1,629 | 1,179 | |
transupp.h | D | 12-May-2024 | 9.8 KiB | 211 | 73 | |
turbojpeg-jni.c | D | 12-May-2024 | 45.8 KiB | 1,247 | 997 | |
turbojpeg-mapfile | D | 12-May-2024 | 989 | 66 | 61 | |
turbojpeg-mapfile.jni | D | 12-May-2024 | 3.1 KiB | 102 | 96 | |
turbojpeg.c | D | 12-May-2024 | 71.5 KiB | 2,154 | 1,721 | |
turbojpeg.h | D | 12-May-2024 | 72.3 KiB | 1,746 | 241 | |
usage.txt | D | 12-May-2024 | 34.2 KiB | 636 | 520 | |
wizard.txt | D | 12-May-2024 | 10.2 KiB | 213 | 175 | |
wrbmp.c | D | 12-May-2024 | 17.8 KiB | 559 | 371 | |
wrgif.c | D | 12-May-2024 | 13.1 KiB | 414 | 211 | |
wrjpgcom.1 | D | 12-May-2024 | 2.6 KiB | 104 | 103 | |
wrjpgcom.c | D | 12-May-2024 | 17.5 KiB | 592 | 396 | |
wrppm.c | D | 12-May-2024 | 10.8 KiB | 366 | 228 | |
wrrle.c | D | 12-May-2024 | 9.2 KiB | 310 | 175 | |
wrtarga.c | D | 12-May-2024 | 7.5 KiB | 262 | 158 |
README.OpenSource
1[ 2{ 3"Name": " libjpeg-turbo ", 4"License": " JPEG License ", 5"License File": " LICENSE.md ", 6"Version Number": " 2.0.5 ", 7"Owner": " lizhiqi1@huawei.com ", 8"Upstream URL": " https://libjpeg-turbo.org/ ", 9"Description": " libjpeg-turbo is a JPEG image codec that uses SIMD instructions. " 10} 11]
README.ijg
1libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project 2to include only information relevant to libjpeg-turbo, to wordsmith certain 3sections, and to remove impolitic language that existed in the libjpeg v8 4README. It is included only for reference. Please see README.md for 5information specific to libjpeg-turbo. 6 7 8The Independent JPEG Group's JPEG software 9========================================== 10 11This distribution contains a release of the Independent JPEG Group's free JPEG 12software. You are welcome to redistribute this software and to use it for any 13purpose, subject to the conditions under LEGAL ISSUES, below. 14 15This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, 16Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, 17Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, 18and other members of the Independent JPEG Group. 19 20IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee 21(also known as JPEG, together with ITU-T SG16). 22 23 24DOCUMENTATION ROADMAP 25===================== 26 27This file contains the following sections: 28 29OVERVIEW General description of JPEG and the IJG software. 30LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 31REFERENCES Where to learn more about JPEG. 32ARCHIVE LOCATIONS Where to find newer versions of this software. 33FILE FORMAT WARS Software *not* to get. 34TO DO Plans for future IJG releases. 35 36Other documentation files in the distribution are: 37 38User documentation: 39 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, 40 rdjpgcom, and wrjpgcom. 41 *.1 Unix-style man pages for programs (same info as usage.txt). 42 wizard.txt Advanced usage instructions for JPEG wizards only. 43 change.log Version-to-version change highlights. 44Programmer and internal documentation: 45 libjpeg.txt How to use the JPEG library in your own programs. 46 example.txt Sample code for calling the JPEG library. 47 structure.txt Overview of the JPEG library's internal structure. 48 coderules.txt Coding style rules --- please read if you contribute code. 49 50Please read at least usage.txt. Some information can also be found in the JPEG 51FAQ (Frequently Asked Questions) article. See ARCHIVE LOCATIONS below to find 52out where to obtain the FAQ article. 53 54If you want to understand how the JPEG code works, we suggest reading one or 55more of the REFERENCES, then looking at the documentation files (in roughly 56the order listed) before diving into the code. 57 58 59OVERVIEW 60======== 61 62This package contains C software to implement JPEG image encoding, decoding, 63and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 64method for full-color and grayscale images. JPEG's strong suit is compressing 65photographic images or other types of images that have smooth color and 66brightness transitions between neighboring pixels. Images with sharp lines or 67other abrupt features may not compress well with JPEG, and a higher JPEG 68quality may have to be used to avoid visible compression artifacts with such 69images. 70 71JPEG is lossy, meaning that the output pixels are not necessarily identical to 72the input pixels. However, on photographic content and other "smooth" images, 73very good compression ratios can be obtained with no visible compression 74artifacts, and extremely high compression ratios are possible if you are 75willing to sacrifice image quality (by reducing the "quality" setting in the 76compressor.) 77 78This software implements JPEG baseline, extended-sequential, and progressive 79compression processes. Provision is made for supporting all variants of these 80processes, although some uncommon parameter settings aren't implemented yet. 81We have made no provision for supporting the hierarchical or lossless 82processes defined in the standard. 83 84We provide a set of library routines for reading and writing JPEG image files, 85plus two sample applications "cjpeg" and "djpeg", which use the library to 86perform conversion between JPEG and some other popular image file formats. 87The library is intended to be reused in other applications. 88 89In order to support file conversion and viewing software, we have included 90considerable functionality beyond the bare JPEG coding/decoding capability; 91for example, the color quantization modules are not strictly part of JPEG 92decoding, but they are essential for output to colormapped file formats or 93colormapped displays. These extra functions can be compiled out of the 94library if not required for a particular application. 95 96We have also included "jpegtran", a utility for lossless transcoding between 97different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 98applications for inserting and extracting textual comments in JFIF files. 99 100The emphasis in designing this software has been on achieving portability and 101flexibility, while also making it fast enough to be useful. In particular, 102the software is not intended to be read as a tutorial on JPEG. (See the 103REFERENCES section for introductory material.) Rather, it is intended to 104be reliable, portable, industrial-strength code. We do not claim to have 105achieved that goal in every aspect of the software, but we strive for it. 106 107We welcome the use of this software as a component of commercial products. 108No royalty is required, but we do ask for an acknowledgement in product 109documentation, as described under LEGAL ISSUES. 110 111 112LEGAL ISSUES 113============ 114 115In plain English: 116 1171. We don't promise that this software works. (But if you find any bugs, 118 please let us know!) 1192. You can use this software for whatever you want. You don't have to pay us. 1203. You may not pretend that you wrote this software. If you use it in a 121 program, you must acknowledge somewhere in your documentation that 122 you've used the IJG code. 123 124In legalese: 125 126The authors make NO WARRANTY or representation, either express or implied, 127with respect to this software, its quality, accuracy, merchantability, or 128fitness for a particular purpose. This software is provided "AS IS", and you, 129its user, assume the entire risk as to its quality and accuracy. 130 131This software is copyright (C) 1991-2016, Thomas G. Lane, Guido Vollbeding. 132All Rights Reserved except as specified below. 133 134Permission is hereby granted to use, copy, modify, and distribute this 135software (or portions thereof) for any purpose, without fee, subject to these 136conditions: 137(1) If any part of the source code for this software is distributed, then this 138README file must be included, with this copyright and no-warranty notice 139unaltered; and any additions, deletions, or changes to the original files 140must be clearly indicated in accompanying documentation. 141(2) If only executable code is distributed, then the accompanying 142documentation must state that "this software is based in part on the work of 143the Independent JPEG Group". 144(3) Permission for use of this software is granted only if the user accepts 145full responsibility for any undesirable consequences; the authors accept 146NO LIABILITY for damages of any kind. 147 148These conditions apply to any software derived from or based on the IJG code, 149not just to the unmodified library. If you use our work, you ought to 150acknowledge us. 151 152Permission is NOT granted for the use of any IJG author's name or company name 153in advertising or publicity relating to this software or products derived from 154it. This software may be referred to only as "the Independent JPEG Group's 155software". 156 157We specifically permit and encourage the use of this software as the basis of 158commercial products, provided that all warranty or liability claims are 159assumed by the product vendor. 160 161 162The IJG distribution formerly included code to read and write GIF files. 163To avoid entanglement with the Unisys LZW patent (now expired), GIF reading 164support has been removed altogether, and the GIF writer has been simplified 165to produce "uncompressed GIFs". This technique does not use the LZW 166algorithm; the resulting GIF files are larger than usual, but are readable 167by all standard GIF decoders. 168 169We are required to state that 170 "The Graphics Interchange Format(c) is the Copyright property of 171 CompuServe Incorporated. GIF(sm) is a Service Mark property of 172 CompuServe Incorporated." 173 174 175REFERENCES 176========== 177 178We recommend reading one or more of these references before trying to 179understand the innards of the JPEG software. 180 181The best short technical introduction to the JPEG compression algorithm is 182 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 183 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 184(Adjacent articles in that issue discuss MPEG motion picture compression, 185applications of JPEG, and related topics.) If you don't have the CACM issue 186handy, a PDF file containing a revised version of Wallace's article is 187available at http://www.ijg.org/files/Wallace.JPEG.pdf. The file (actually 188a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 189omits the sample images that appeared in CACM, but it includes corrections 190and some added material. Note: the Wallace article is copyright ACM and IEEE, 191and it may not be used for commercial purposes. 192 193A somewhat less technical, more leisurely introduction to JPEG can be found in 194"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 195M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 196good explanations and example C code for a multitude of compression methods 197including JPEG. It is an excellent source if you are comfortable reading C 198code but don't know much about data compression in general. The book's JPEG 199sample code is far from industrial-strength, but when you are ready to look 200at a full implementation, you've got one here... 201 202The best currently available description of JPEG is the textbook "JPEG Still 203Image Data Compression Standard" by William B. Pennebaker and Joan L. 204Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 205Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 206standards (DIS 10918-1 and draft DIS 10918-2). 207 208The original JPEG standard is divided into two parts, Part 1 being the actual 209specification, while Part 2 covers compliance testing methods. Part 1 is 210titled "Digital Compression and Coding of Continuous-tone Still Images, 211Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 21210918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 213Continuous-tone Still Images, Part 2: Compliance testing" and has document 214numbers ISO/IEC IS 10918-2, ITU-T T.83. 215 216The JPEG standard does not specify all details of an interchangeable file 217format. For the omitted details, we follow the "JFIF" conventions, revision 2181.02. JFIF version 1 has been adopted as ISO/IEC 10918-5 (05/2013) and 219Recommendation ITU-T T.871 (05/2011): Information technology - Digital 220compression and coding of continuous-tone still images: JPEG File Interchange 221Format (JFIF). It is available as a free download in PDF file format from 222https://www.iso.org/standard/54989.html and http://www.itu.int/rec/T-REC-T.871. 223A PDF file of the older JFIF 1.02 specification is available at 224http://www.w3.org/Graphics/JPEG/jfif3.pdf. 225 226The TIFF 6.0 file format specification can be obtained by FTP from 227ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 228found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 229IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 230Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 231(Compression tag 7). Copies of this Note can be obtained from 232http://www.ijg.org/files/. It is expected that the next revision 233of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 234Although IJG's own code does not support TIFF/JPEG, the free libtiff library 235uses our library to implement TIFF/JPEG per the Note. 236 237 238ARCHIVE LOCATIONS 239================= 240 241The "official" archive site for this software is www.ijg.org. 242The most recent released version can always be found there in 243directory "files". 244 245The JPEG FAQ (Frequently Asked Questions) article is a source of some 246general information about JPEG. 247It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 248and other news.answers archive sites, including the official news.answers 249archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 250If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 251with body 252 send usenet/news.answers/jpeg-faq/part1 253 send usenet/news.answers/jpeg-faq/part2 254 255 256FILE FORMAT COMPATIBILITY 257========================= 258 259This software implements ITU T.81 | ISO/IEC 10918 with some extensions from 260ITU T.871 | ISO/IEC 10918-5 (JPEG File Interchange Format-- see REFERENCES). 261Informally, the term "JPEG image" or "JPEG file" most often refers to JFIF or 262a subset thereof, but there are other formats containing the name "JPEG" that 263are incompatible with the DCT-based JPEG standard or with JFIF (for instance, 264JPEG 2000 and JPEG XR). This software therefore does not support these 265formats. Indeed, one of the original reasons for developing this free software 266was to help force convergence on a common, interoperable format standard for 267JPEG files. 268 269JFIF is a minimal or "low end" representation. TIFF/JPEG (TIFF revision 6.0 as 270modified by TIFF Technical Note #2) can be used for "high end" applications 271that need to record a lot of additional data about an image. 272 273 274TO DO 275===== 276 277Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. 278
README.md
1Background 2========== 3 4libjpeg-turbo is a JPEG image codec that uses SIMD instructions to accelerate 5baseline JPEG compression and decompression on x86, x86-64, ARM, PowerPC, and 6MIPS systems, as well as progressive JPEG compression on x86 and x86-64 7systems. On such systems, libjpeg-turbo is generally 2-6x as fast as libjpeg, 8all else being equal. On other types of systems, libjpeg-turbo can still 9outperform libjpeg by a significant amount, by virtue of its highly-optimized 10Huffman coding routines. In many cases, the performance of libjpeg-turbo 11rivals that of proprietary high-speed JPEG codecs. 12 13libjpeg-turbo implements both the traditional libjpeg API as well as the less 14powerful but more straightforward TurboJPEG API. libjpeg-turbo also features 15colorspace extensions that allow it to compress from/decompress to 32-bit and 16big-endian pixel buffers (RGBX, XBGR, etc.), as well as a full-featured Java 17interface. 18 19libjpeg-turbo was originally based on libjpeg/SIMD, an MMX-accelerated 20derivative of libjpeg v6b developed by Miyasaka Masaru. The TigerVNC and 21VirtualGL projects made numerous enhancements to the codec in 2009, and in 22early 2010, libjpeg-turbo spun off into an independent project, with the goal 23of making high-speed JPEG compression/decompression technology available to a 24broader range of users and developers. 25 26 27License 28======= 29 30libjpeg-turbo is covered by three compatible BSD-style open source licenses. 31Refer to [LICENSE.md](LICENSE.md) for a roll-up of license terms. 32 33 34Building libjpeg-turbo 35====================== 36 37Refer to [BUILDING.md](BUILDING.md) for complete instructions. 38 39 40Using libjpeg-turbo 41=================== 42 43libjpeg-turbo includes two APIs that can be used to compress and decompress 44JPEG images: 45 46- **TurboJPEG API**<br> 47 This API provides an easy-to-use interface for compressing and decompressing 48 JPEG images in memory. It also provides some functionality that would not be 49 straightforward to achieve using the underlying libjpeg API, such as 50 generating planar YUV images and performing multiple simultaneous lossless 51 transforms on an image. The Java interface for libjpeg-turbo is written on 52 top of the TurboJPEG API. The TurboJPEG API is recommended for first-time 53 users of libjpeg-turbo. Refer to [tjexample.c](tjexample.c) and 54 [TJExample.java](java/TJExample.java) for examples of its usage and to 55 <http://libjpeg-turbo.org/Documentation/Documentation> for API documentation. 56 57- **libjpeg API**<br> 58 This is the de facto industry-standard API for compressing and decompressing 59 JPEG images. It is more difficult to use than the TurboJPEG API but also 60 more powerful. The libjpeg API implementation in libjpeg-turbo is both 61 API/ABI-compatible and mathematically compatible with libjpeg v6b. It can 62 also optionally be configured to be API/ABI-compatible with libjpeg v7 and v8 63 (see below.) Refer to [cjpeg.c](cjpeg.c) and [djpeg.c](djpeg.c) for examples 64 of its usage and to [libjpeg.txt](libjpeg.txt) for API documentation. 65 66There is no significant performance advantage to either API when both are used 67to perform similar operations. 68 69Colorspace Extensions 70--------------------- 71 72libjpeg-turbo includes extensions that allow JPEG images to be compressed 73directly from (and decompressed directly to) buffers that use BGR, BGRX, 74RGBX, XBGR, and XRGB pixel ordering. This is implemented with ten new 75colorspace constants: 76 77 JCS_EXT_RGB /* red/green/blue */ 78 JCS_EXT_RGBX /* red/green/blue/x */ 79 JCS_EXT_BGR /* blue/green/red */ 80 JCS_EXT_BGRX /* blue/green/red/x */ 81 JCS_EXT_XBGR /* x/blue/green/red */ 82 JCS_EXT_XRGB /* x/red/green/blue */ 83 JCS_EXT_RGBA /* red/green/blue/alpha */ 84 JCS_EXT_BGRA /* blue/green/red/alpha */ 85 JCS_EXT_ABGR /* alpha/blue/green/red */ 86 JCS_EXT_ARGB /* alpha/red/green/blue */ 87 88Setting `cinfo.in_color_space` (compression) or `cinfo.out_color_space` 89(decompression) to one of these values will cause libjpeg-turbo to read the 90red, green, and blue values from (or write them to) the appropriate position in 91the pixel when compressing from/decompressing to an RGB buffer. 92 93Your application can check for the existence of these extensions at compile 94time with: 95 96 #ifdef JCS_EXTENSIONS 97 98At run time, attempting to use these extensions with a libjpeg implementation 99that does not support them will result in a "Bogus input colorspace" error. 100Applications can trap this error in order to test whether run-time support is 101available for the colorspace extensions. 102 103When using the RGBX, BGRX, XBGR, and XRGB colorspaces during decompression, the 104X byte is undefined, and in order to ensure the best performance, libjpeg-turbo 105can set that byte to whatever value it wishes. If an application expects the X 106byte to be used as an alpha channel, then it should specify `JCS_EXT_RGBA`, 107`JCS_EXT_BGRA`, `JCS_EXT_ABGR`, or `JCS_EXT_ARGB`. When these colorspace 108constants are used, the X byte is guaranteed to be 0xFF, which is interpreted 109as opaque. 110 111Your application can check for the existence of the alpha channel colorspace 112extensions at compile time with: 113 114 #ifdef JCS_ALPHA_EXTENSIONS 115 116[jcstest.c](jcstest.c), located in the libjpeg-turbo source tree, demonstrates 117how to check for the existence of the colorspace extensions at compile time and 118run time. 119 120libjpeg v7 and v8 API/ABI Emulation 121----------------------------------- 122 123With libjpeg v7 and v8, new features were added that necessitated extending the 124compression and decompression structures. Unfortunately, due to the exposed 125nature of those structures, extending them also necessitated breaking backward 126ABI compatibility with previous libjpeg releases. Thus, programs that were 127built to use libjpeg v7 or v8 did not work with libjpeg-turbo, since it is 128based on the libjpeg v6b code base. Although libjpeg v7 and v8 are not 129as widely used as v6b, enough programs (including a few Linux distros) made 130the switch that there was a demand to emulate the libjpeg v7 and v8 ABIs 131in libjpeg-turbo. It should be noted, however, that this feature was added 132primarily so that applications that had already been compiled to use libjpeg 133v7+ could take advantage of accelerated baseline JPEG encoding/decoding 134without recompiling. libjpeg-turbo does not claim to support all of the 135libjpeg v7+ features, nor to produce identical output to libjpeg v7+ in all 136cases (see below.) 137 138By passing an argument of `-DWITH_JPEG7=1` or `-DWITH_JPEG8=1` to `cmake`, you 139can build a version of libjpeg-turbo that emulates the libjpeg v7 or v8 ABI, so 140that programs that are built against libjpeg v7 or v8 can be run with 141libjpeg-turbo. The following section describes which libjpeg v7+ features are 142supported and which aren't. 143 144### Support for libjpeg v7 and v8 Features 145 146#### Fully supported 147 148- **libjpeg API: IDCT scaling extensions in decompressor**<br> 149 libjpeg-turbo supports IDCT scaling with scaling factors of 1/8, 1/4, 3/8, 150 1/2, 5/8, 3/4, 7/8, 9/8, 5/4, 11/8, 3/2, 13/8, 7/4, 15/8, and 2/1 (only 1/4 151 and 1/2 are SIMD-accelerated.) 152 153- **libjpeg API: Arithmetic coding** 154 155- **libjpeg API: In-memory source and destination managers**<br> 156 See notes below. 157 158- **cjpeg: Separate quality settings for luminance and chrominance**<br> 159 Note that the libpjeg v7+ API was extended to accommodate this feature only 160 for convenience purposes. It has always been possible to implement this 161 feature with libjpeg v6b (see rdswitch.c for an example.) 162 163- **cjpeg: 32-bit BMP support** 164 165- **cjpeg: `-rgb` option** 166 167- **jpegtran: Lossless cropping** 168 169- **jpegtran: `-perfect` option** 170 171- **jpegtran: Forcing width/height when performing lossless crop** 172 173- **rdjpgcom: `-raw` option** 174 175- **rdjpgcom: Locale awareness** 176 177 178#### Not supported 179 180NOTE: As of this writing, extensive research has been conducted into the 181usefulness of DCT scaling as a means of data reduction and SmartScale as a 182means of quality improvement. The reader is invited to peruse the research at 183<http://www.libjpeg-turbo.org/About/SmartScale> and draw his/her own conclusions, 184but it is the general belief of our project that these features have not 185demonstrated sufficient usefulness to justify inclusion in libjpeg-turbo. 186 187- **libjpeg API: DCT scaling in compressor**<br> 188 `cinfo.scale_num` and `cinfo.scale_denom` are silently ignored. 189 There is no technical reason why DCT scaling could not be supported when 190 emulating the libjpeg v7+ API/ABI, but without the SmartScale extension (see 191 below), only scaling factors of 1/2, 8/15, 4/7, 8/13, 2/3, 8/11, 4/5, and 192 8/9 would be available, which is of limited usefulness. 193 194- **libjpeg API: SmartScale**<br> 195 `cinfo.block_size` is silently ignored. 196 SmartScale is an extension to the JPEG format that allows for DCT block 197 sizes other than 8x8. Providing support for this new format would be 198 feasible (particularly without full acceleration.) However, until/unless 199 the format becomes either an official industry standard or, at minimum, an 200 accepted solution in the community, we are hesitant to implement it, as 201 there is no sense of whether or how it might change in the future. It is 202 our belief that SmartScale has not demonstrated sufficient usefulness as a 203 lossless format nor as a means of quality enhancement, and thus our primary 204 interest in providing this feature would be as a means of supporting 205 additional DCT scaling factors. 206 207- **libjpeg API: Fancy downsampling in compressor**<br> 208 `cinfo.do_fancy_downsampling` is silently ignored. 209 This requires the DCT scaling feature, which is not supported. 210 211- **jpegtran: Scaling**<br> 212 This requires both the DCT scaling and SmartScale features, which are not 213 supported. 214 215- **Lossless RGB JPEG files**<br> 216 This requires the SmartScale feature, which is not supported. 217 218### What About libjpeg v9? 219 220libjpeg v9 introduced yet another field to the JPEG compression structure 221(`color_transform`), thus making the ABI backward incompatible with that of 222libjpeg v8. This new field was introduced solely for the purpose of supporting 223lossless SmartScale encoding. Furthermore, there was actually no reason to 224extend the API in this manner, as the color transform could have just as easily 225been activated by way of a new JPEG colorspace constant, thus preserving 226backward ABI compatibility. 227 228Our research (see link above) has shown that lossless SmartScale does not 229generally accomplish anything that can't already be accomplished better with 230existing, standard lossless formats. Therefore, at this time it is our belief 231that there is not sufficient technical justification for software projects to 232upgrade from libjpeg v8 to libjpeg v9, and thus there is not sufficient 233technical justification for us to emulate the libjpeg v9 ABI. 234 235In-Memory Source/Destination Managers 236------------------------------------- 237 238By default, libjpeg-turbo 1.3 and later includes the `jpeg_mem_src()` and 239`jpeg_mem_dest()` functions, even when not emulating the libjpeg v8 API/ABI. 240Previously, it was necessary to build libjpeg-turbo from source with libjpeg v8 241API/ABI emulation in order to use the in-memory source/destination managers, 242but several projects requested that those functions be included when emulating 243the libjpeg v6b API/ABI as well. This allows the use of those functions by 244programs that need them, without breaking ABI compatibility for programs that 245don't, and it allows those functions to be provided in the "official" 246libjpeg-turbo binaries. 247 248Those who are concerned about maintaining strict conformance with the libjpeg 249v6b or v7 API can pass an argument of `-DWITH_MEM_SRCDST=0` to `cmake` prior to 250building libjpeg-turbo. This will restore the pre-1.3 behavior, in which 251`jpeg_mem_src()` and `jpeg_mem_dest()` are only included when emulating the 252libjpeg v8 API/ABI. 253 254On Un*x systems, including the in-memory source/destination managers changes 255the dynamic library version from 62.2.0 to 62.3.0 if using libjpeg v6b API/ABI 256emulation and from 7.2.0 to 7.3.0 if using libjpeg v7 API/ABI emulation. 257 258Note that, on most Un*x systems, the dynamic linker will not look for a 259function in a library until that function is actually used. Thus, if a program 260is built against libjpeg-turbo 1.3+ and uses `jpeg_mem_src()` or 261`jpeg_mem_dest()`, that program will not fail if run against an older version 262of libjpeg-turbo or against libjpeg v7- until the program actually tries to 263call `jpeg_mem_src()` or `jpeg_mem_dest()`. Such is not the case on Windows. 264If a program is built against the libjpeg-turbo 1.3+ DLL and uses 265`jpeg_mem_src()` or `jpeg_mem_dest()`, then it must use the libjpeg-turbo 1.3+ 266DLL at run time. 267 268Both cjpeg and djpeg have been extended to allow testing the in-memory 269source/destination manager functions. See their respective man pages for more 270details. 271 272 273Mathematical Compatibility 274========================== 275 276For the most part, libjpeg-turbo should produce identical output to libjpeg 277v6b. The one exception to this is when using the floating point DCT/IDCT, in 278which case the outputs of libjpeg v6b and libjpeg-turbo can differ for the 279following reasons: 280 281- The SSE/SSE2 floating point DCT implementation in libjpeg-turbo is ever so 282 slightly more accurate than the implementation in libjpeg v6b, but not by 283 any amount perceptible to human vision (generally in the range of 0.01 to 284 0.08 dB gain in PNSR.) 285 286- When not using the SIMD extensions, libjpeg-turbo uses the more accurate 287 (and slightly faster) floating point IDCT algorithm introduced in libjpeg 288 v8a as opposed to the algorithm used in libjpeg v6b. It should be noted, 289 however, that this algorithm basically brings the accuracy of the floating 290 point IDCT in line with the accuracy of the slow integer IDCT. The floating 291 point DCT/IDCT algorithms are mainly a legacy feature, and they do not 292 produce significantly more accuracy than the slow integer algorithms (to put 293 numbers on this, the typical difference in PNSR between the two algorithms 294 is less than 0.10 dB, whereas changing the quality level by 1 in the upper 295 range of the quality scale is typically more like a 1.0 dB difference.) 296 297- If the floating point algorithms in libjpeg-turbo are not implemented using 298 SIMD instructions on a particular platform, then the accuracy of the 299 floating point DCT/IDCT can depend on the compiler settings. 300 301While libjpeg-turbo does emulate the libjpeg v8 API/ABI, under the hood it is 302still using the same algorithms as libjpeg v6b, so there are several specific 303cases in which libjpeg-turbo cannot be expected to produce the same output as 304libjpeg v8: 305 306- When decompressing using scaling factors of 1/2 and 1/4, because libjpeg v8 307 implements those scaling algorithms differently than libjpeg v6b does, and 308 libjpeg-turbo's SIMD extensions are based on the libjpeg v6b behavior. 309 310- When using chrominance subsampling, because libjpeg v8 implements this 311 with its DCT/IDCT scaling algorithms rather than with a separate 312 downsampling/upsampling algorithm. In our testing, the subsampled/upsampled 313 output of libjpeg v8 is less accurate than that of libjpeg v6b for this 314 reason. 315 316- When decompressing using a scaling factor > 1 and merged (AKA "non-fancy" or 317 "non-smooth") chrominance upsampling, because libjpeg v8 does not support 318 merged upsampling with scaling factors > 1. 319 320 321Performance Pitfalls 322==================== 323 324Restart Markers 325--------------- 326 327The optimized Huffman decoder in libjpeg-turbo does not handle restart markers 328in a way that makes the rest of the libjpeg infrastructure happy, so it is 329necessary to use the slow Huffman decoder when decompressing a JPEG image that 330has restart markers. This can cause the decompression performance to drop by 331as much as 20%, but the performance will still be much greater than that of 332libjpeg. Many consumer packages, such as Photoshop, use restart markers when 333generating JPEG images, so images generated by those programs will experience 334this issue. 335 336Fast Integer Forward DCT at High Quality Levels 337----------------------------------------------- 338 339The algorithm used by the SIMD-accelerated quantization function cannot produce 340correct results whenever the fast integer forward DCT is used along with a JPEG 341quality of 98-100. Thus, libjpeg-turbo must use the non-SIMD quantization 342function in those cases. This causes performance to drop by as much as 40%. 343It is therefore strongly advised that you use the slow integer forward DCT 344whenever encoding images with a JPEG quality of 98 or higher. 345 346 347Memory Debugger Pitfalls 348======================== 349 350Valgrind and Memory Sanitizer (MSan) can generate false positives 351(specifically, incorrect reports of uninitialized memory accesses) when used 352with libjpeg-turbo's SIMD extensions. It is generally recommended that the 353SIMD extensions be disabled, either by passing an argument of `-DWITH_SIMD=0` 354to `cmake` when configuring the build or by setting the environment variable 355`JSIMD_FORCENONE` to `1` at run time, when testing libjpeg-turbo with Valgrind, 356MSan, or other memory debuggers. 357