Archive-name: compression-faq/part1 Last-modified: June 9th, 1993 "I've already explained this once, but repetition is the very soul of the net." (from alt.config) This file is part 1 of a set of Frequently Asked Questions (FAQ) for the groups comp.compression and comp.compression.research. (If you can't find part 2 or 3, see item 53 below.) Certain questions get asked time and again, and this is an attempt to reduce the bandwidth taken up by these posts and their associated replies. If you have a question, *please* check this file before you post. It may save a lot of peoples time. If you have not already read the overall Usenet introductory material posted to "news.announce.newusers", please do. If you don't want to see this FAQ regularly, please add the subject line to your kill file. If you have corrections or suggestions for this FAQ, send them to Jean-loup Gailly . Thank you. Part 1 is oriented towards practical usage of compression programs. Part 2 is more intended for people who want to know how compression works. Part 3 is a long list of image compression hardware. Main changes relative to the previous version: - added suffix .gz and updated gzip version (item 2) - new version of presskit (item 2) - added pointer to old 'squeeze' (item 2) - new data compression patents as usual (item 8) - added pointer to a new wavelet image compression program (item 15) Contents ======== General questions: [1] What are these newsgroups about? [2] What is this .xxx file type? Where can I find the corresponding compression program? [3] What is the latest pkzip version? [4] What is an archiver? [5] What is the best general purpose compression program? [7] Which books should I read? [8] What about patents on data compression algorithms? [9] The WEB 16:1 compressor. [11] What is the V.42bis standard? [12] I need source for the winners of the Dr Dobbs compression contest [13] I need source for arithmetic coding Image and audio compression: [15] Where can I get image compression programs? [16] What is the state of the art in lossless image compression? [17] What is the state of fractal compression? [18] I need specs and source for TIFF and CCITT group 4 Fax. [19] What is JPEG? [20] I am looking for source of an H.261 codec and MPEG [25] Fast DCT (Discrete Cosine Transform) algorithms [26] Are there algorithms and standards for audio compression? Common problems: [30] My archive is corrupted! [31] pkunzip reports a CRC error! [32] VMS zip is not compatible with pkzip! [33] I have a problem with Stacker! Questions which do not really belong to comp.compression: [50] What is this 'tar' compression program? [51] I need a CRC algorithm [52] What about those people who continue to ask frequently asked questions? [53] Where are FAQ lists archived? [54] I need specs for graphics formats [55] Where can I find Lenna and other images? [56] I am looking for a message digest algorithm Part 2: (Long) introductions to data compression techniques [70] Introduction to data compression (long) Huffman and Related Compression Techniques Arithmetic Coding Substitutional Compressors The LZ78 family of compressors The LZ77 family of compressors [71] Introduction to MPEG (long) What is MPEG? Does it have anything to do with JPEG? Then what's JBIG and MHEG? What has MPEG accomplished? So how does MPEG I work? What about the audio compression? So how much does it compress? What's phase II? When will all this be finished? How do I join MPEG? How do I get the documents, like the MPEG I draft? [72] What is wavelet theory? [73] What is the theoretical compression limit? [74] Introduction to JBIG [75] Introduction to JPEG Part 3: (Long) list of image compression hardware [85] Image compression hardware [99] Acknowledgments Search for "Subject: [#]" to get to question number # quickly. Some news readers can also take advantage of the message digest format used here. If you know very little about data compression, read question 70 in part 2 first. ------------------------------------------------------------------------------ Subject: [1] What are these newsgroups about? comp.compression is the place to discuss about data compression, both lossless (for text or data) and lossy (for images, sound, etc..). comp.compression.research was created later to provide a forum for current research on data compression and data compression algorithms. If you are not experienced in data compression, please post in comp.compression only. If you only want to find a particular compression program for a particular operating system, please read first this FAQ and the article "How to find sources" which is regularly posted in news.answers. If you can't resist posting such a request, other groups are probably more appropriate (comp.binaries.ibm.pc.wanted, comp.sources.wanted, comp.sys.mac.wanted, comp.archives.msdos.d, alt.graphics.pixutils). Please post your request in comp.compression only as a last resource. If your question is about graphics only (no compression), please post to comp.graphics, *after* reading the comp.graphics FAQ (see item 54 below). For some unknown reason, many questions about graphics are incorrectly posted to comp.compression. Please do not post any program in binary form to comp.compression. Very short sources can be posted, but long sources should be be posted to the specialized source groups, such as comp.sources.* or alt.sources. As for any newsgroups, do not post the same message separately to comp.compression and comp.compression.research. ------------------------------------------------------------------------------ Subject: [2] What is this .xxx file type? Where can I find the corresponding compression program? All the programs mentioned in this section are lossless. For most programs, one US and one European ftp site are given. (wuarchive.wustl.edu: 128.152.135.4, garbo.uwasa.fi: 128.214.87.1) Many other sites (in particular wsmr-simtel20.army.mil: 192.88.110.2) have the same programs. To keep this list to a reasonable size, many programs are not mentioned here. Additional information can be found in the file ftp.cso.uiuc.edu:/doc/pcnet/compression [128.174.5.61] maintained by David Lemson (lemson@uiuc.edu). When several programs can handle the same archive format, only one of them is given. Sources for additional lossless data compressors can be found in garbo.uwasa.fi:/pc/programming/lds_10.zip and oak.oakland.edu:/pub/msdos/archivers/lz-comp2.zip. Sources in Pascal are in garbo.uwasa.fi:/pc/turbopas/preskit2.zip. For Macintosh programs, look on sumex-aim.stanford.edu:/info-mac [36.44.0.6]. For VM/CMS, look on vmd.cso.uiuc.edu:/public.477 [128.174.5.98]. For Atari, look on atari.archive.umich.edu [141.211.165.41] For Amiga, look on ftp.cso.uiuc.edu:/pub/amiga [128.174.5.59] If you don't know how to use ftp or don't have ftp access, read the article "How to find sources" which is regularly posted in news.answers. If you can't find a program given below, it is likely that a newer version exists in the same directory. (Tell me ) A very short description of the compression algorithm is given for most programs. For the meaning of LZ77, LZ78 and LZW, see question 70 in part 2 of the FAQ.) ext: produced by or read by .arc: arc, pkarc for MSDOS. (LZW algorithm) wuarchive.wustl.edu:/mirrors/msdos/starter/pk361.exe garbo.uwasa.fi:/pc/arcers/pk361.exe arc for Unix wuarchive.wustl.edu:/mirrors/misc/unix/arc521e.tar-z garbo.uwasa.fi:/unix/arcers/arc.tar.Z Contact: Howard Chu arc for VMS wuarchive.wustl.edu:/packages/compression/vax-vms/arc.exe arcmac for Mac mac.archive.umich.edu:/mac/utilities/compressionapps/arcmac.hqx arc for Amiga ftp.funet.fi:pub/amiga/fish/001-100/ff070/arc.lha .arj: arj for MSDOS (LZ77 with hashing, plus secondary static Huffman encoding on a block basis) Contact: Robert K Jung wuarchive.wustl.edu:/mirrors/msdos/archivers/arj230.exe garbo.uwasa.fi:/pc/arcers/arj230ng.exe garbo.uwasa.fi:/pc/arcers/arj239b.exe unarj for Unix. Decompresses only. (There is no arj compressor for Unix. Don't post a request.) wuarchive.wustl.edu:/mirrors/misc/unix/unarj230.tar-z garbo.uwasa.fi:/unix/arcers/unarj230.tar.Z unarj for Mac mac.archive.umich.edu:/mac/util/compression/unarjmac.cpt.hqx unarj for Amiga ftp.funet.fi:pub/amiga/utilities/archivers/unarj-0.5.lha .cpt: Compact Pro for Mac sumex-aim.stanford.edu:/info-mac/util/compact-pro-133.hqx [36.44.0.6] For Unix: sumex-aim.stanford.edu:/info-mac/unix/macutil-20b1.shar ftp.cwi.nl:/pub/macutil2.0b3.shar.Z .gif: gif files are images compressed with the LZW algorithm. See the comp.graphics FAQ list for programs manipulating .gif files. See suffix .Z below for source of LZW. .gz, .z: gzip (or pack, see .z below). gzip uses the same algorithm as zip 1.9 (see below); it can also extract packed and compressed files. For Unix, MSDOS, OS/2, VMS, Atari, Amiga, Primos: prep.ai.mit.edu:/pub/gnu/gzip-1.1.2.tar (or .shar or .tar.z : source) prep.ai.mit.edu:/pub/gnu/gzip-msdos-1.1.2.exe (msdos, lha self-extract) garbo.uwasa.fi:/unix/arcers/gzip-1.1.1.tar.Z (source) garbo.uwasa.fi:/pc/arcers/gzip111.exe (msdos exe, self-extract) oak.oakland.edu:/pub/msdos/compress/gzip111.zip (msdos exe) ftp.spc.edu:[.macro32.savesets]gzip-1-1-1.zip (vms source & exe) sumex-aim.stanford.edu:/info-mac/tmit/gzip.hqx (Macintosh exe) .ha: ha 0.98 for MSDOS (improved PPMC - 4th order Markov modeling) garbo.uwasa.fi:/pc/arcers/ha098.exe .hqx: Macintosh BinHex format.. (BinHex is *not* a compression program, it is similar to uuencode but handles multiple forks.) for Mac: mac.archive.umich.edu:/mac/utilities/compressionapps/binhex4.0.bin for Unix: sumex-aim.stanford.edu:/info-mac/unix/mcvert-165.shar [36.44.0.6] for MSDOS: wuarchive.wustl.edu:/mirrors/msdos/xbin23.zip .lha: .lzh: lha for MSDOS (LZ77 with a trie data structure, plus secondary static Huffman coding on a block basis) wuarchive.wustl.edu:/mirrors/msdos/archivers/lha213.exe (exe) wuarchive.wustl.edu:/mirrors/msdos/archivers/lha211sr.zip (sources) garbo.uwasa.fi:/pc/arcers/lha213.exe lharc for Unix. (LZ77 with hash table and binary trees, plus secondary Huffman coding) Warning: lharc can extract .lzh files created by lharc 1.xx but not those created by lha. See lha for Unix below. wuarchive.wustl.edu:/mirrors/misc/unix/lharc102a.tar-z garbo.uwasa.fi:/unix/arcers/lharcsrc.zoo lharc for VMS. Same warning as for Unix lharc. wuarchive.wustl.edu:/packages/compression/vax-vms/lharc.exe lha for Unix. Warning: all doc is in Japanese. wuarchive.wustl.edu:/mirrors/misc/unix/lha101u.tar-z garbo.uwasa.fi:/unix/arcers/lha-1.00.tar.Z Contact: lha-admin@oki.co.jp or oki@wbg.telcom.oki.co.jp lha for Mac mac.archive.umich.edu:/mac/utilities/compressionapps/maclha2.0.cpt.hqx lha for Amiga ftp.funet.fi:pub/amiga/utilities/archivers/LhA_e138.run .pak: pak for MSDOS (LZW algorithm) wuarchive.wustl.edu:/mirrors/msdos/archivers/pak251.exe garbo.uwasa.fi:/pc/arcers/pak251.exe .pit: PackIt (Macintosh) for Mac: sumex-aim.stanford.edu:/info-mac/util/stuffit-151.hqx [36.44.0.6] for Unix: sumex-aim.stanford.edu:/info-mac/unix/mcvert-165.shar [36.44.0.6] .pp: PowerPacker (Amiga) ftp.funet.fi:pub/amiga/fish/501-600/ff561/PPLib.lha .sea: self-extracting archive (Macintosh) Run the file to extract it. The self-extraction code can be removed with: mac.archive.umich.edu:/mac/utilities/compressionapps/desea1.11.cpt.hqx .shar: Shell archive. This is not a compression program. Use "sh foo.shar" to extract. .sit: Stuffit for Macintosh for Mac: sumex-aim.stanford.edu:/info-mac/util/stuffit-lite-30.hqx [36.44.0.6] for Unix: sumex-aim.stanford.edu:/info-mac/unix/unsit-15.shar [36.44.0.6] for Amiga: ftp.funet.fi:pub/amiga/utilities/archivers/unsit-1.5c2.lha for MSDOS: garbo.uwasa.fi:/pc/arcers/unsit30.zip .?q?: Squeeze for MSDOS (do not confuse with other 'squeeze' below). Static Huffman coding. oak.oakland.edu:/pub/msdos/starter/sqpc12a.com (squeeze) oak.oakland.edu:/pub/msdos/starter/nusq110.com (unsqueeze) .sqz: Squeeze for MSDOS (do not confuse with other 'squeeze' above) LZ77 with hashing. wuarchive.wustl.edu:/mirrors/msdos/archivers/sqz1083e.exe garbo.uwasa.fi:/pc/arcers/sqz1083e.exe .tar: tar is *not* a compression program. However, to be kind for you: for MSDOS wuarchive.wustl.edu:/mirrors/msdos/starter/tarread.exe garbo.uwasa.fi:/pc/unix/tar4dos.zoo for Unix tar (you have it already. To extract: tar xvf file.tar) for VMS wuarchive.wustl.edu:/packages/compression/vax-vms/tar.exe for Macintosh sumex-aim.stanford.edu:/info-mac/util/tar-30.hqx for Amiga: ftp.funet.fi:pub/amiga/fish/401-500/ff445/Tar.lha .tar.Z, .tar-z, .taz: tar + compress For Unix: zcat file.tar.Z | tar xvf - with GNU tar: tar xvzf file.tar.Z Other OS: first uncompress (see .Z below) then untar (see .tar above) .tar.z, .tgz: tar + gzip For Unix: gzip -cd file.tar.z | tar xvf - with GNU tar: tar xvzf file.tar.z Other OS: first uncompress (see .z below) then untar (see .tar above) .z: pack or gzip (see .gz above). pack uses static Huffman coding. To extract, see .gz above. .zip: pkzip 1.10 for MSDOS. (LZ77 with hashing, plus secondary static Shannon-Fano encoding on whole file) Contact: pkware.inc@mixcom.com wuarchive.wustl.edu:/mirrors/msdos/zip/pkz110eu.exe. garbo.uwasa.fi:/pc/arcers/pkz110eu.exe. Note: pkz110eu.exe is an 'export' version without encryption. zip 1.1 for Unix, MSDOS, VMS, OS/2, ... (compatible with pkzip 1.10. For corresponding unzip, see unzip 5.0p1 below). wuarchive.wustl.edu:/mirrors/misc/unix/zip11.zip arcutil 2.0 for VM/CMS (unzip only, not yet compatible with pkzip 2.04) vmd.cso.uiuc.edu:/public.477/arcutil.* [128.174.5.98]. pkzip 2.04g for MSDOS. (LZ77 with hashing, plus secondary static Huffman coding on a block basis) garbo.uwasa.fi:/pc/arcers/pkz204g.exe ftp.cica.indiana.edu:/pub/pc/starter/pkz204g.exe. zip 1.9p1 and unzip 5.0p1 for Unix, MSDOS, VMS, OS/2, Amiga, ... Compatible with pkzip 2.04g (LZ77 with hashing, plus secondary static Huffman coding on a block basis) Contact: zip-bugs@wkuvx1.bitnet oak.oakland.edu:/pub/misc/unix/zip19p1.zip (source) oak.oakland.edu:/pub/misc/unix/unz50p1.tar-z (tar.Z source) oak.oakland.edu:/pub/msdos/zip/zip19p1x.zip (MSDOS exe) oak.oakland.edu:/pub/msdos/zip/unz50p1.exe (MSDOS exe) wuarchive.wustl.edu:/mirrors/garbo.uwasa.fi/arcutil/zcrypt19.zip (encryption source. Non US residents must get it from garbo,see below) garbo.uwasa.fi:/unix/arcers/zip19p1.zip (source) garbo.uwasa.fi:/unix/arcers/unz50p1.tar.Z (source) garbo.uwasa.fi:/pc/arcers/zip19p1x.zip (MSDOS exe) garbo.uwasa.fi:/pc/arcers/unz50p1.exe (MSDOS exe) ftp.luth.se:/pub/amiga/util/arc/InfoZipI.lha (amiga exe zip+unzip) garbo.uwasa.fi:/pc/arcutil/zcrypt19.zip (encryption source) ftp.win.tue.nl:/pub/compression/zip/zcryp19x.zip (crypt MSDOS exe) for Macintosh (zip-it and unzip-201 are compatible with pkzip 2.04) sumex-aim.stanford.edu:/info-mac/util/zip-it-111.hqx sumex-aim.stanford.edu:/info-mac/util/unzip-201.hqx sumex-aim.stanford.edu:/info-mac/util/mac-zip-10.hqx .zoo: zoo 2.10 for MSDOS (algorithm copied from that of lha, see lha above) Contact: Rahul Dhesi wuarchive.wustl.edu:/mirrors/msdos/zoo/zoo210.exe garbo.uwasa.fi:/pc/arcers/zoo210.exe zoo 2.10 for Unix, VMS wsmr-simtel20.army.mil:pd8:zoo210.tar-z [192.88.110.2] garbo.uwasa.fi:/unix/arcers/zoo210.tar.Z zoo for Mac mac.archive.umich.edu:/mac/utilities/compressionapps/maczoo.sit.hqx zoo for Amiga ftp.funet.fi:pub/amiga/utilities/archivers/Zoo-2.1.lha .F: freeze for Unix (LZ77 with hashing, plus secondary dynamic Huffman encoding) wuarchive.wustl.edu:/usenet/comp.sources.misc/volume25/freeze/part0[1-2].Z ftp.inria.fr:/system/arch-compr/freeze-2.3.4.tar.Z Contact: Leonid A. Broukhis .Y: yabba for Unix, VMS, ... (Y coding, a variant of LZ78) wuarchive.wustl.edu:/usenet/comp.sources.unix/volume24/yabbawhap/part0[1-4].Z ftp.inria.fr:/system/arch-compr/yabba.tar.Z Contact: Dan Bernstein .Z: compress for Unix ('the' LZW algorithm) It is likely that your Unix system has 'compress' already. Otherwise: wuarchive.wustl.edu:/packages/compression/compress-4.1.tar (not in .Z format to avoid chicken and egg problem) compress for MSDOS wuarchive.wustl.edu:/mirrors/msdos/compress/comp430[ds].zip garbo.uwasa.fi:/pc/unix/comp430d.zip compress for Macintosh sumex-aim.stanford.edu:/info-mac/util/maccompress-32.hqx compress for Amiga ftp.funet.fi:pub/amiga/utilities/archivers/compress-4.1.lha compress for Vax/VMS wuarchive.wustl.edu:/packages/compression/vax-vms/lzcomp.exe wuarchive.wustl.edu:/packages/compression/vax-vms/lzdcmp.exe ------------------------------------------------------------------------------ Subject: [3] What is the latest PKZIP version? The latest official version is 2.04g. Release 2.04c had serious bugs, corrected in 2.04e and 2.04g. Be warned that there are countless bogus PKZIP 1.20, 2.0, 2.02, 3.05 and whatever scams floating around. They usually are hacks of PKZIP 1.93A beta test version. Some of them are trojans and / or carry computer virii. ------------------------------------------------------------------------------ Subject: [4] What is an archiver? There is a distinction between archivers and other compression programs: - an archiver takes several input files, compresses them and produces a single archive file. Examples are arc, arj, lha, zip, zoo. - other compression programs create one compressed file for each input file. Examples are freeze, yabba, compress. Such programs are often combined with tar to create compressed archives (see question 50: "What is this tar compression program?"). ------------------------------------------------------------------------------ Subject: [5] What is the best general purpose compression program? The answer is: it depends. (You did not expect a definitive answer, did you?) It depends whether you favor speed, compression ratio, a standard and widely used archive format, the number of features, etc... Just as for text editors, personal taste plays an important role. compress has 4 options, arj 2.30 has about 130 options; different people like different programs. *Please* do not start or continue flame wars on such matters of taste. The only objective comparisons are speed and compression ratio. Here is a short table comparing various programs on a 33Mhz Compaq 386. All programs have been run on Unix SVR4, except pkzip and arj which only run on MSDOS. (MSDOS benchmarks are available by ftp on oak.oakland.edu:/pub/msdos/info/arctst*.zip.) *Please* do not post your own benchmarks made on your own files that nobody else can access. If you think that you must absolutely post yet another benchmark, make sure that your test files are available by anonymous ftp. The programs compared here were chosen because they are the most popular or because they run on Unix and source is available. For ftp information, see above. Three programs (hpack, comp-2 and ha) have been added because they achieve better compression (at the expense of speed) and one program (lzrw3-a) has been added because it favors speed at the expense of compression: - comp-2 is in wuarchive.wustl.edu:/mirrors/msdos/ddjmag/ddj9102.zip (inner zip file nelson.zip), - hpack is in wuarchive.wustl.edu:/mirrors/misc/unix/hpack75a.tar-z and garbo.uwasa.fi:/unix/arcers/hpack78src.tar.Z - ha 0.98 is in garbo.uwasa.fi:/pc/arcers/ha098.zip - ftp.adelaide.edu.au:/pub/compression/lzrw3-a.c [129.127.40.3] The 14 files used in the comparison are from the standard Calgary Text Compression Corpus, available by ftp on fsa.cpsc.ucalgary.ca [136.159.2.1] in /pub/text.compression.corpus/text.compression.corpus.tar.Z. The whole corpus includes 18 files, but the 4 files paper[3-6] are generally omitted in benchmarks. It contains several kinds of file (ascii, binary, image, etc...) but has a bias towards large files. You may well get different ratings on the typical mix of files that you use daily, so keep in mind that the comparisons given below are only indicative. The programs are ordered by decreasing total compressed size. For a fair comparison between archivers and other programs, this size is only the size of the compressed data, not the archive size. The programs were run on an idle machine, so the elapsed time is significant and can be used to compare Unix and MSDOS programs. [Note: I did not have time to run again all benchmarks with freeze 2.4. To be done for next revision of this FAQ.] size lzrw3a compress lharc yabba pkzip freeze version: 4.0 1.02 1.0 1.10 2.3.5 options: -m300000 ------ ----- ------ ------ ------ ------ ------ bib 111261 49040 46528 46502 40456 41354 41515 book1 768771 416131 332056 369479 306813 350560 344793 book2 610856 274371 250759 252540 229851 232589 230861 geo 102400 84214 77777 70955 76695 76172 68626 news 377109 191291 182121 166048 168287 157326 155783 obj1 21504 12647 14048 10748 13859 10546 10453 obj2 246814 108040 128659 90848 114323 90130 85500 paper1 53161 24522 25077 21748 22453 20041 20021 paper2 82199 39479 36161 35275 32733 32867 32693 pic 513216 111000 62215 61394 65377 63805 53291 progc 39611 17919 19143 15399 17064 14164 14143 progl 71646 24358 27148 18760 23512 17255 17064 progp 49379 16801 19209 12792 16617 11877 11686 trans 93695 30292 38240 28092 31300 23135 22861 3,141,622 1,400,105 1,259,141 1,200,580 1,159,340 1,141,821 1,109,290 real 0m35s 0m59s 5m03s 2m40s 5m27s user 0m25s 0m29s 4m29s 1m46s 4m58s sys 0m05s 0m10s 0m07s 0m18s 0m08s MSDOS: 1m39s zoo lha arj pkzip zip hpack comp-2 ha 2.10 1.0(Unix) 2.30 2.04g 1.9 0.75a 0.98 ah 2.13(MSDOS) -jm -ex -6 a2 ------ ------ ------ ------ ------- ------ ------ ------ bib 40742 40740 36090 35186 34950 35619 29840 26927 book1 339076 339074 318382 313566 312619 306876 237380 235733 book2 228444 228442 210521 207204 206306 208486 174085 163535 geo 68576 68574 69209 68698 68418 58976 64590 59356 news 155086 155084 146855 144954 144395 141608 128047 123335 obj1 10312 10310 10333 10307 10295 10572 10819 9799 obj2 84983 84981 82052 81213 81336 80806 85465 80381 paper1 19678 19676 18710 18519 18525 18607 16895 15675 paper2 32098 32096 30034 29566 29674 29825 25453 23956 pic 52223 52221 53578 52777 55051 51778 55461 51639 progc 13943 13941 13408 13363 13238 13475 12896 11795 progl 16916 16914 16408 16148 16175 16586 17354 15298 progp 11509 11507 11308 11214 11182 11647 11668 10498 trans 22580 22578 20046 19808 18879 20506 21023 17927 1,096,166 1,096,138 1,036,934 1,019,451 1,021,043 1,005,367 890,976 845,854 real 4m07s 6m03s 1m49s 1h22m17s 27m05s user 3m47s 4m23s 1m43s 1h20m46s 19m27s sys 0m04s 0m08s 0m02s 0m12s 2m03s MSDOS: 1m49s 2m41s 1m43s 14m43s Notes: - the compressed data for 'zoo ah' is always two bytes longer than for lha. This is simply because both programs are derived from the same source (ar002, written by Haruhiko Okumura, available by ftp in wuarchive.wustl.edu:/mirrors/msdos/archivers/ar002.zip). - hpack 0.75a gives slightly different results on SunOS. (To be checked with 0.78). - the MSDOS versions are all optimized with assembler code and were run on a RAM disk. So it is not surprising that they often go faster than their Unix equivalent. ------------------------------------------------------------------------------ Subject: [7] Which books should I read? [BWC 1989] Bell, T.C, Witten, I.H, and Cleary, J.G. "Text Compression", Prentice-Hall 1989. ISBN: 0-13-911991-4. Price: approx. US$40 The reference on text data compression. [Nel 1991] Mark Nelson, "The Data Compression Book" M&T Books, Redwood City, CA, 1991. ISBN 1-55851-216-0. Price $36.95 including two 5" PC-compatible disks bearing all the source code printed in the book. A practical introduction to data compression. The book is targeted at a person who is comfortable reading C code but doesn't know anything about data compression. Its stated goal is to get you up to the point where you are competent to program standard compression algorithms. [Will 1990] Williams, R. "Adaptive Data Compression", Kluwer Books, 1990. ISBN: 0-7923-9085-7. Price: US$75. Reviews the field of text data compression and then addresses the problem of compressing rapidly changing data streams. [Stor 1988] Storer, J.A. "Data Compression: Methods and Theory", Computer Science Press, Rockville, MD. ISBN: 0-88175-161-8. A survey of various compression techniques, mainly statistical non-arithmetic compression and LZSS compression. Includes complete Pascal code for a series of LZ78 variants. [ACG 1991] Advances in Speech Coding, edited by Atal, Cuperman, and Gersho, Kluwer Academic Press, 1991. [GG 1991] Vector Quantization and Signal Compression, by Gersho and Gray, Kluwer Acad. Press, 1991 [CT 1991] Elements of Information Theory, by T.M.Cover and J.A.Thomas John Wiley & Sons, 1991. ISBN 0-471-06259-6. Review papers: [BWC 1989] Bell, T.C, Witten, I.H, and Cleary, J.G. "Modeling for Text Compression", ACM Computing Surveys, Vol.21, No.4 (December 1989), p.557 A good general overview of compression techniques (as well as modeling for text compression); the condensed version of "Text Compression". [Lele 1987] Lelewer, D.A, and Hirschberg, D.S. "Data Compression", ACM Computing Surveys, Vol.19, No.3 (September 1987), p.261. A survey of data compression techniques which concentrates on Huffman compression and makes only passing mention of other techniques. ------------------------------------------------------------------------------ Subject: [8] What about patents on data compression algorithms? [Note: the appropriate group for discussing software patents is comp.patents (or misc.legal.computing), not comp.compression.] All patents mentioned here are US patents, and thus probably not applicable outside the US. See item 70, "Introduction to data compression" for the meaning of LZ77, LZ78 or LZW. (a) Run length encoding - Tsukiyama has two patents on run length encoding: 4,586,027 and 4,872,009 granted in 1986 and 1989 respectively. The first one covers run length encoding in its most primitive form: a length byte followed by the repeated byte. The second patent covers the 'invention' of limiting the run length to 16 bytes and thus the encoding of the length on 4 bits. Here is the start of claim 1 of patent 4,872,009, just for pleasure: 1. A method of transforming an input data string comprising a plurality of data bytes, said plurality including portions of a plurality of consecutive data bytes identical to one another, wherein said data bytes may be of a plurality of types, each type representing different information, said method comprising the steps of: [...] - O'Brien has patented (4,988,998) run length encoding followed by LZ77. (b) LZ77 - Waterworth patented (4,701,745) the algorithm now known as LZRW1, because Ross Williams reinvented it later and posted it on comp.compression on April 22, 1991. (See item 5 for the ftp site with all LZRW derivatives.) The *same* algorithm has later been patented by Gibson & Graybill (see below). The patent office failed to recognize that the same algorithm was patented twice, even though the wording used in the two patents is very similar. The Waterworth patent is now owned by Stac Inc, and used as the basis of a lawsuit against Microsoft, concerning the compression feature of MSDOS 6.0. - Fiala and Greene obtained in 1990 a patent (4,906,991) on all implementations of LZ77 using a tree data structure. Claim 1 of the patent is much broader than the algorithms published by Fiala and Greene in Comm.ACM, April 89. The patent covers the algorithm published by Rodeh and Pratt in 1981 (J. of the ACM, vol 28, no 1, pp 16-24). It also covers the algorithm previously patented by Eastman-Lempel-Ziv (4,464,650), and the algorithms used in lharc, lha and zoo. - Notenboom (from Microsoft) 4,955,066 uses three levels of compression, starting with run length encoding. - The Gibson & Graybill patent 5,049,881 covers the LZRW1 algorithm previously patented by Waterworth and reinvented by Ross Williams. Claims 4 and 12 are very general and could be interpreted as applying to any LZ algorithm using hashing (including all variants of LZ78): 4. A compression method for compressing a stream of input data into a compressed stream of output data based on a minimum number of characters in each input data string to be compressed, said compression method comprising the creation of a hash table, hashing each occurrence of a string of input data and subsequently searching for identical strings of input data and if such an identical string of input data is located whose string size is at least equal to the minimum compression size selected, compressing the second and all subsequent occurrences of such identical string of data, if a string of data is located which does not match to a previously compressed string of data, storing such data as uncompressed data, and for each input strings after each hash is used to find a possible previous match location of the string, the location of the string is stored in the hash table, thereby using the previously processed data to act as a compression dictionary. Claim 12 is identical, with 'method' replaced with 'apparatus'. Since the 'minimal compression size' can be as small as 2, the claim could cover any dictionary technique of the LZ family. However the text of the patent and the other claims make clear that the patent should cover the LZRW1 algorithm only. (In any case the Gibson & Graybill patent is likely to be invalid because of the prior art in the Waterworth patent.) - Phil Katz, author of pkzip, also has a patent on LZ77 (5,051,745) but the claims only apply to sorted hash tables, and when the hash table is substantially smaller than the window size. - IBM patented (5,001,478) the idea of combining a history buffer (the LZ77 technique) and a lexicon (as in LZ78). - Stac Inc patented (5,016,009 and 5,126,739) yet another variation of LZ77 with hashing. The '009 patent is used in the lawsuit against Microsoft (see above). Stac also has patents on LZ77 with parallel lookup in hardware (4,841,092 and 5,003,307). - Robert Jung, author of 'arj', has been granted patent 5,140,321 for one variation of LZ77 with hashing. This patent covers the LZRW3-A algorithm, also previously discovered by Ross Williams. LZRW3-A was posted on comp.compression on July 15, 1991. The patent was filed two months later on Sept 4, 1991. (The US patent system allows this because of the 'invention date' rule.) - Chambers 5,155,484 is yet another variation of LZ77 with hashing. The hash function is just the juxtaposition of two input bytes, this is the 'invention' being patented. The hash table is named 'direct lookup table'. (c) LZ78 - One form of the original LZ78 algorithm was patented (4,464,650) by its authors Lempel, Ziv, Cohn and Eastman. - The LZW algorithm used in 'compress'is patented by IBM (4,814,746) and Unisys (4,558,302). It is also used in the V.42bis compression standard (see question 11 on V.42bis below) and in Postscript Level 2. (Unisys sells the license to modem manufacturers for a onetime $25,000 fee.) The IBM patent application was filed three weeks before that of Unisys, but the US patent office failed to recognize that they covered the same algorithm. (The IBM patent is more general, but its claim 7 is exactly LZW.) - AP coding is patented by Storer (4,876,541). (Get the yabba package for source code, see question 2 above, file type .Y) (d) arithmetic coding - IBM holds many patents on arithmetic coding (4,286,256 4,295,125 4,463,342 4,467,317 4,633,490 4,652,856 4,891,643 4,905,297 4,935,882). It has patented in particular the Q-coder implementation of arithmetic coding. The arithmetic coding option of the JPEG standard requires use of the patented algorithm. No JPEG-compatible method is possible without infringing the patent, because what IBM actually claims rights to is the underlying probability model (the heart of an arithmetic coder). (See the JPEG FAQ for details.) AT&T has 3 patents on arithmetic coding (4,973,961, 5,023,611, 5,025,258). As can be seen from the above list, some of the most popular compression programs (compress, pkzip, zoo, lha, arj) are now covered by patents. (This says nothing about the validity of these patents.) Here are some references on data compression patents. A number of them are taken from the list prep.ai.mit.edu:/pub/lpf/patent-list. 3,914,586 Data compression method and apparatus filed 10/25/73, granted 10/21/75 General Motors Corporation, Detroit MI Duane E. McIntosh, Santa Ynez CA Data compression apparatus is disclosed is operable in either a bit pair coding mode of a word coding mode depending on the degree of redundancy of the data to be encoded. 3,976,844 Data communication system for transmitting data in compressed form filed Apr. 4, 1975, granted Aug. 24, 1976 inventor Bernard K. Betz, assignee Honeywell Information Systems, Inc. [encode differences with previous line] 4,021,782 Data compaction system and apparatus inventor Hoerning filed 04/30/1975, granted 05/03/1977 [A primitive form of LZ77 with implicit offsets (compare with previous record)] 4,054,951 Data expansion apparatus inventor R.D. Jackson, assignee IBM filed Jun. 30, 1976, granted Oct. 18, 1977 [Covers only decompression of data compressed with a variant of LZ77.] 4,087,788 Data compression system filed 1/14/77, granted 5/2/78 NCR Canada LTD - NCR Canada Ltee, Mississauga CA Brian J. Johannesson, Waterloo CA A data compression system is disclosed in which the left hand boundary of a character is developed in the form of a sequence of Freeman direction codes, the codes being stored in digital form within a processor. 4,286,256 Method and means for arithmetic coding using a reduced number of operations. granted Aug 25, 1981 assignee IBM 4,295,125 A method and means for pipeline decoding of the high to low order pairwise combined digits of a decodable set of relatively shifted finite number of strings granted Oct 13, 1981 assignee IBM 4,412,306 System for minimizing space requirements for storage and transmission of digital signals filed May 14, 1981, granted Oct. 25, 1983 inventor Edward W. Moll 4,463,342 A method and means for carry-over control in a high order to low order combining of digits of a decodable set of relatively shifted finite number strings. granted Jul 31, 1984 assignee IBM 4,491,934 Data compression process filed May 12, 1982, granted Jan. 1, 1985 inventor Karl E. Heinz 4,464,650 Apparatus and method for compressing data signals and restoring the compressed data signals inventors Lempel, Ziv, Cohn, Eastman assignees Sperry Corporation and At&T Bell Laboratories filed 8/10/81, granted 8/7/84 A compressor parses the input data stream into segments where each segment comprises a prefix and the next symbol in the data stream following the prefix. 4,467,317 High-speed arithmetic compression using using concurrent value updating. granted Aug 21, 1984 assignee IBM 4,494,108 Adaptive source modeling for data file compression within bounded memory filed Jun. 5, 1984, granted Jan. 15, 1985 invntors Glen G. Langdon, Jorma J. Rissanen assignee IBM order 1 Markov modeling 4,558,302 High speed data compression and decompression apparatus and method inventor Welch assignee Sperry Corporation (now Unisys) filed 6/20/83, granted 12/10/85 The text for this patent can be ftped from rusmv1.rus.uni-stuttgart.de (129.69.1.12) in /info/comp.patents/US4558302.Z. 4,560,976 Data compression filed 6/5/84, granted 12/24/85 Codex Corporation, Mansfield MA Steven G. Finn, Framingham, MA A stream of source characters, which occur with varying relative frequencies, is encoded into a compressed stream of codewords, each having one, two or three subwords, by ranking the source characters by their current frequency of appearance, encoding the source characters having ranks no higher than a first number as one subword codewords, source characters having ranks higher than the first number but no higher than a second number as two subword codewords, and the remaining source characters as three subword codewords. 4,586,027 Method and system for data compression and restoration inventor Tsukimaya et al. assignee Hitachi filed 08/07/84, granted 04/29/86 4,597,057 System for compressed storate of 8-bit ascii bytes using coded strings of 4-bit nibbles. inventor Snow, assignee System Development corporation. filed 12/31/1981, granted 06/24/1986. Compression using static dictionary of common words, prefixes and suffixes. 4,612,532 Data compression apparatus and method inventor Bacon, assignee Telebyte Corportion filed Jun. 19, 1984, granted Sep. 16, 1986 [Uses followsets as in the pkzip 0.92 'reduce' algorithm, but the followsets are dynamically updated. This is in effect a sort of order-1 Markov modeling.] 4,622,545 Method and apparatus for image compression and Manipulation inventor William D. Atkinson assignee Apple computer Inc. filed 9/30/82 granted 11/11/86 4,633,490 Symmetrical adaptive data compression/decompression system. granted Dec 30, 1985 assignee IBM 4,652,856 A multiplication-free multi-alphabet arithmetic code. granted Feb 4, 1986 assignee IBM 4,667,649 Data receiving apparatus filed 4/18/84, granted 6/30/87 inventors Kunishi et al. assignee Canon Kabushiki Kaisha, Tokyo Japan compression of Fax images. 4,682,150 Data compression method and apparatus inventors Mathes and Protheroe, assignee NCR Corporation, Dayton OH A system and apparatus for compressing redundant and nonredundant binary data generated as part of an operation of a time and attendance terminal in which the data represents the time an employee is present during working hours. 4,701,745 Data compression system inventor Waterworth John R assignee Ferranti PLC GB, patent rights now acquired by Stac Inc. filed 03/03/1986 (03/06/1985 in GB), granted 10/20/1987 Algorithm now known as LZRW1 (see above) I claim: 1. A data compression system comprising an input store for receiving and storing a plurality of bytes of uncompressed data from an outside source, and data processing means for processing successive bytes of data from the input store; the data processing means including circuit means operable to check whether a sequence of successive bytes to be processed identical with a sequence of bytes already processed, and including hash generating means responsive to the application of a predetermined number of bytes in sequence to derive a hash code appropriate to those bytes, a temporary store in which the hash code may represent the address of a storage location, and a pointer counter operable to store in the temporary store at said address a pointer indicative of the position in the input store of one of the predetermined number of bytes; output means operable to apply to a transfer medium each byte of data not forming part of such an identical sequence; and encoding means responsive to the identification of such a sequence to apply to the transfer medium an identification signal which identifies both the location in the input store of the previous occurrence of the sequence of bytes and the number of bytes contained in the sequence. 4,730,348 Adaptive data compression system inventor MacCrisken, assignee Adaptive Computer Technologies filed Sep. 19, 1986, granted Mar. 8, 1988 [order-1 Markov modeling + Huffman coding + LZ77] 4,758,899 Data compression control device inventor Tsukiyama, assignee Hitachi filed 11/20/1985, granted 07/19/1988 Limits compression to ensure that tape drive stays busy. 4,809,350 Data compression system filed Jan. 30, 1987, granted Feb. 28, 1989 inventor Yair Shimoni & Ron Niv assignee Elscint Ltd., Haifa, Israel [Image compression via variable length encoding of differences with predicted data.] 4,814,746 Data compression method inventors Victor S. Miller, Mark N. Wegman assignee IBM filed 8/11/86, granted 3/21/89 A previous application was filed on 6/1/83, three weeks before the application by Welch (4,558,302) Communications between a Host Computing System and a number of remote terminals is enhanced by a data compression method which modifies the data compression method of Lempel and Ziv by addition of new character and new string extensions to improve the compression ratio, and deletion of a least recently used routine to limit the encoding tables to a fixed size to significantly improve data transmission efficiency. 4,853,696 Code converter for data compression/decompression filed 4/13/87, granted 8/1/89 inventor Amar Mukherjee, Maitland FL assignee University of Central Florida, Orlando FL Another hardware Huffman encoder: A code converter has a network of logic circuits connected in reverse binary tree fashion with logic paths between leaf nodes and a common root node. 4,872,009 Method and apparatus for data compression and restoration inventor Tsukimaya et al. assignee Hitachi filed 12/07/87, granted 10/03/89 This patent on run length encoding covers the 'invention' of limiting the run length to 16 bytes and thus the encoding of the length on 4 bits. 4,876,541 Stem [sic] for dynamically compressing and decompressing electronic data filed 10/15/87, granted 10/24/89 inventor James A. Storer assignee Data Compression Corporation A data compression system for encoding and decoding textual data, including an encoder for encoding the data and for a decoder for decoding the encoded data. 4,891,643 Arithmetic coding data compression/de-compression by selectively employed, diverse arithmetic encoders and decoders. granted Jan 2, 1990 assignee IBM 4,905,297 granted Feb 27, 1990 assignee IBM Arithmetic coding encoder and decoder system. 4,906,991 Textual substitution data compression with finite length search window filed 4/29/1988, granted 3/6/1990 inventors Fiala,E.R., and Greene,D.H. assignee Xerox Corporation 4,935,882 Probability adaptation for arithmetic coders. granted Jun 19, 1990 assignee IBM 4,941,193 Barnsley, fractal compression. 4,943,869 Compression Method for Dot Image Data filed 1988-05-04, granted 1990-07-24 assignee Fuji Photo Film Co. Lossy and lossless image compression schemes. 4,955,066 Compressing and Decompressing Text Files filed 10/13/89, granted 09/04/90 inventor Notenboom, L.A. assignee Microsoft Now extended as 5,109,433 [Noted in signon screen of Word 5.5 and on the outside of the MS-DOS 5.0 Upgrade.] A method of compressing a text file in digital form is disclosed. A full text file having characters formed into phrases is provided by an author. The characters are digitally represented by bytes. A first pass compression is sequentially followed by a second pass compression of the text which has previously been compressed. A third or fourth level of compression is serially performed on the compressed text. For example, in a first pass, the text is run-length compressed. In a second pass, the compressed text is further compressed with key phrase compression. In a third pass, the compressed text is further compressed with Huffman compression. The compressed text is stored in a text file having a Huffman decode tree, a key phrase table, and a topic index. The data is decompressed in a single pass and provided one line at a time as an output. Sequential compressing of the text minimizes the storage space required for the file. Decompressing of the text is performed in a single pass. As a complete line is decompressed, it is output rapidly, providing full text to the user. 4,973,961 Method and apparatus for carry-over control in arithmetic coding. granted Nov 27, 1990 assignee AT&T 4,988,998 Data compression system for successively applying at least two data compression methods to an input data stream. inventor O'Brien assignee Storage Technology Corporation, Louisville, Colorado filed Sep 5, 1989, granted Jan 29, 1991. Run length encoding followed by LZ77. 5,001,478 Method of Encoding Compressed Data filed 12/28/89, granted 03/19/91 inventor Michael E. Nagy assignee IBM 1. A method of encoding a compressed data stream made up of a sequence of literal references, lexicon references and history references, which comprises the steps of: assigning to each literal reference a literal identifier; assigning to each history reference a history identifier; assigning to each lexicon reference a lexicon identifier; and emitting a data stream with said identifiers assigned to said references. Gordon Irlam says: The invention can probably be best understood by considering the decompressor. It consists of a history buffer, and a lexicon buffer, both of which are initially empty. The history buffer contains the last n symbols emitted. Whenever a history buffer reference is to be output the string so referenced is subsequently moved to the lexicon buffer for future reference. Thus the history buffer keeps track of strings that may be repeated on a very short term basis, while the lexicon buffer stores items for a longer time. Furthermore a history reference involves specifying both the offset and length within the history buffer, whereas a lexicon reference simply specifies a number denoting the string. Both buffers have a finite size. 5,003,307 Data compression apparatus with shift register search means filed Oct. 6, 1989, granted Mar. 26, 1991 inventors George Glen A, Ivey Glen E, Whiting Douglas L assignee Stac Inc continuation of 4,841,092 5,016,009 Data compression apparatus and method filed 01/13/1989, granted 05/14/1991 inventors George Glen A, Ivey Glen E, Whiting Douglas L assignee Stac Inc LZ77 with offset hash table (extended in 5,126,739) 5,023,611 Entropy encoder/decoder including a context extractor. granted Jun 11, 1991 assignee AT&T 5,025,258 Adaptive probability estimator for entropy encoder/decoder. granted Jun 18, 1991 assignee AT&T 5,049,881 Apparatus and method for very high data rate-compression incorporating lossless data compression and expansion utilizing a hashing technique inventors Dean K. Gibson, Mark D. Graybill assignee Intersecting Concepts, Inc. filed 6/18/90, granted 9/17/91 [covers lzrw1, almost identical with Waterworth 4,701,745] 5,051,745 String searcher, and compressor using same filed 8/21/90, granted 9/24/91 inventor Phillip W. Katz (author of pkzip) In the string search method and apparatus pointers to the string to be searched are indexed via a hashing function and organized according to the hashing values of the string elements pointed to. The hashing function is also run on the string desired to be found, and the resulting hashing value is used to access the index. If the resulting hashing value is not in the index, it is known that the target string does not appear in the string being searched. Otherwise the index is used to determine the pointers which correspond to the target hashing value, these pointers pointing to likely candidates for matching the target string. The pointers are then used to sequentially compare each of the locations in the string being searched to the target string, to determine whether each location contains a match to the target string. In the method and apparatus for compressing a stream of data symbols, a fixed length search window, comprising a predetermined contiguous portion of the symbol stream, is selected as the string to be searched by the string searcher. If a string to be compressed is found in the symbol stream, a code is output designating the location within the search window of the matching string and the length of the matching string. 5,065,447 Barnsley, fractal compression 5,109,433 Compressing and decompressing text files inventor Notenboom assignee Microsoft extension of 4,955,066 5,126,739 Data Compression Apparatus and Method filed Nov. 27, 1990, granted June 30, 1992. inventor Whiting et. al assignee Stac Inc LZ77 with offset hash table (extension of 5,016,009) 5,140,321 Data compression/decompression method and apparatus filed 9/4/91, granted 8/18/92 inventor Robert Jung assignee Prime Computer 5,155,484 Fast data compressor with direct lookup table indexing into history buffer filed 9/13/1991, granted 10/13/1992 inventor Chambers, IV, Lloyd L., Menlo Park, California assignee Salient Software, Inc., Palo Alto, California (02) Uses a 64K hash table indexed by the first two characters of the input string. Includes several claims on the LZ77 file format (literal or offset,length). 5,179,378 file Jul. 30, 1991, granted Jan. 12, 1993 inventor Ranganathan assignee University of South Florida Method and apparatus for the compression and decompression of data using Lempel-Ziv based techniques. [This covers LZ77 hardware compression with a systolic array of processors working in parallel.] Japan 2-46275 Coding system granted Feb 26, 1990 [Patents one form of arithmetic coding.] ------------------------------------------------------------------------------ Subject: [9] The WEB 16:1 compressor. [WARNING: this topic has generated the greatest volume of news in the history of comp.compression. Read this before posting on this subject.] (a) What the press says April 20, 1992 Byte Week Vol 4. No. 25: "In an announcement that has generated high interest - and more than a bit of skepticism - WEB Technologies (Smyrna, GA) says it has developed a utility that will compress files of greater than 64KB in size to about 1/16th their original length. Furthermore, WEB says its DataFiles/16 program can shrink files it has already compressed." [...] "A week after our preliminary test, WEB showed us the program successfully compressing a file without losing any data. But we have not been able to test this latest beta release ourselves." [...] "WEB, in fact, says that virtually any amount of data can be squeezed to under 1024 bytes by using DataFiles/16 to compress its own output multiple times." June 1992 Byte, Vol 17 No 6: [...] According to Earl Bradley, WEB Technologies' vice president of sales and marketing, the compression algorithm used by DataFiles/16 is not subject to the laws of information theory. [...] (b) First details, by John Wallace : I called WEB at (404)514-8000 and they sent me some product literature as well as chatting for a few minutes with me on the phone. Their product is called DataFiles/16, and their claims for it are roughly those heard on the net. According to their flier: "DataFiles/16 will compress all types of binary files to approximately one-sixteenth of their original size ... regardless of the type of file (word processing document, spreadsheet file, image file, executable file, etc.), NO DATA WILL BE LOST by DataFiles/16." (Their capitalizations; 16:1 compression only promised for files >64K bytes in length.) "Performed on a 386/25 machine, the program can complete a compression/decompression cycle on one megabyte of data in less than thirty seconds" "The compressed output file created by DataFiles/16 can be used as the input file to subsequent executions of the program. This feature of the utility is known as recursive or iterative compression, and will enable you to compress your data files to a tiny fraction of the original size. In fact, virtually any amount of computer data can be compressed to under 1024 bytes using DataFiles/16 to compress its own output files muliple times. Then, by repeating in reverse the steps taken to perform the recusive compression, all original data can be decompressed to its original form without the loss of a single bit." Their flier also claims: "Constant levels of compression across ALL TYPES of FILES" "Convenient, single floppy DATA TRANSPORTATION" From my telephone conversation, I was was assured that this is an actual compression program. Decompression is done by using only the data in the compressed file; there are no hidden or extra files. (c) More information, by Rafael Ramirez : Today (Tuesday, 28th) I got a call from Earl Bradley of Web who now says that they have put off releasing a software version of the algorithm because they are close to signing a major contract with a big company to put the algorithm in silicon. He said he could not name the company due to non-disclosure agreements, but that they had run extensive independent tests of their own and verified that the algorithm works. [...] He said the algorithm is so simple that he doesn't want anybody getting their hands on it and copying it even though he said they have filed a patent on it. [...] Mr. Bradley said the silicon version would hold up much better to patent enforcement and be harder to copy. He claimed that the algorithm takes up about 4K of code, uses only integer math, and the current software implementation only uses a 65K buffer. He said the silicon version would likely use a parallel version and work in real-time. [...] (d) The impossiblity proofs. It is impossible for a given program to compress without loss *all* files greater than a certain size by at least one bit. This can be proven by a simple counting argument. (Many other proofs have been posted on comp.compression, *please* do not post yet another one.) Assume that the program can compress without loss all files of size >= N bits. Compress with this program all the 2^N files which have exactly N bits. All compressed files have at most N-1 bits, so there are at most (2^N)-1 different compressed files [2^(N-1) files of size N-1, 2^(N-2) of size N-2, and so on, down to 1 file of size 0]. So at least two different input files must compress to the same output file. Hence the compression program cannot be lossless. (Stronger results about the number of incompressible files can be obtained, but the proofs are a little more complex.) This argument applies of course to WEB's case (take N = 64K*8 bits). Note that no assumption is made about the compression algorithm. The proof applies to *any* algorithm, including those using an external dictionary, or repeated application of another algorithm, or combination of different algorithms, or representation of the data as formulas, etc... All schemes are subject to the counting argument. There is no need to use information theory to provide a proof, just basic mathematics. This assumes of course that the information available to the decompressor is only the bit sequence of the compressed data. If external information such as a file name or a number of iterations is necessary to decompress the data, the bits providing the extra information must be included in the bit count of the compressed data. (Otherwise, it would be sufficient to consider any input data as a number, use this as the iteration count or file name, and pretend that the compressed size is zero.) [See also question 73 "What is the theoretical compression limit?" in part 2 of this FAQ.] (e) No software version Appeared on BIX, reposted by Bruce Hoult : tojerry/chaos #673, from abailey, 562 chars, Tue Jun 16 20:40:34 1992 Comment(s). ---------- TITLE: WEB Technology I promised everyone a report when I finally got the poop on WEB's 16:1 data compression. After talking back and forth for a year and being put off for the past month by un-returned phone calls, I finally got hold of Marc Spindler who is their sales manager. _No_ software product is forth coming, period! He began talking about hardware they are designing for delivery at the end of the year. [...] (f) Product cancelled Posted by John Toebes on Aug 10th, 1992: [Long story omitted, confirming the reports made above about the original WEB claims.] 10JUL92 - Called to Check Status. Was told that testing had uncovered a new problem where 'four numbers in a matrix were the same value' and that the programmers were off attempting to code a preprocessor to eliminate this rare case. I indicated that he had told me this story before. He told me that the programmers were still working on the problem. 31JUL92 - Final Call to Check Status. Called Earl in the morning and was told that he still had not heard from the programmers. [...] Stated that if they could not resolve the problem then there would probably not be a product. 03AUG92 - Final Call. Earl claims that the programmers are unable to resolve the problem. I asked if this meant that there would not be a product as a result and he said yes. (g) Conclusion The last report given above should put an end to the WEB story. [Note from the FAQ maintainer: I will keep this long story in the FAQ for a while, and will remove it when the dust has finally settled down.] ------------------------------------------------------------------------------ Subject: [11] What is the V.42bis standard? A description of the V.42bis standard is given in "The V.42bis standard for data-compressing modems," by Clark Thomborson , IEEE Micro, Oct 1992, pp. 41-53. Short introduction, by Alejo Hausner : The V.42bis Compression Standard was proposed by the International Consultative Committee on Telephony and Telegraphy (CCITT) as an addition to the v.42 error-correction protocol for modems. Its purpose is to increase data throughput, and uses a variant of the Lempel-Ziv-Welch (LZW) compression method. It is meant to be implemented in the modem hardware, but can also be built into the software that interfaces to an ordinary non-compressing modem. V.42bis can send data compressed or not, depending on the data. There are some types of data that cannot be compressed. For example, if a file was compressed first, and then sent through a V.42bis modem, the modem would not likely reduce the number of bits sent. Indeed it is likely that the amount of data would increase somewhat. To avoid this problem, the algorithm constantly monitors the compressibility of the data, and if it finds fewer bits would be necessary to send it uncompressed, it switches to transparent mode. The sender informs the receiver of this transition through a reserved escape code. Henceforth the data is passed as plain bytes. The choice of escape code is clever. Initially, it is a zero byte. Any occurrence of the escape code is replaced, as is customary, by two escape codes. In order to prevent a string of escape codes from temporarily cutting throughput in half, the escape code is redefined by adding 51 mod 256 each time it is used. While transmitting in transparent mode, the sender maintains the LZW trees of strings, and expects the receiver to do likewise. If it finds an advantage in returning to compressed mode, it will do so, first informing the receiver by a special control code. Thus the method allows the hardware to adapt to the compressibility of the data. The CCITT standards documents used to be available by ftp on ftp.uu.net in /doc/standards/ccitt, but this service has been discontinued. If you ftp to digital.resource.org, in directory pub/standards there is a file that says that making the standards available in the first place was just an experiment. The documents are now on src.doc.ic.ac.uk, in directory /computing/ccitt/standards/ccitt (they used to be in directory doc/ccitt-standards/ccitt, so look around if you don't find them). The v42bis standard is in /computing/ccitt/standards/ccitt/1992/v/v42bis.asc.Z. A mail server for CCITT documents is available at teledoc@itu.arcom.ch. For more information, contact Robert Shaw or Antoinette Bautista . Warning by John Levine : This teledoc thing is much less than meets the eye. What it actually has is one-page abstracts of some but not all CCITT recommendations, along with junk like lists of the national representatives to CCITT. If you want the actual text of a recommendation, you have to send large amounts of money to Switzerland, same as ever. However, a closer reading of the Teledoc announcement shows that they say they're planning to make the actual text of some CCITT recommendations available on-line sometime in 1993. See also the Standards FAQ posted to news.answers or get it by ftp in rtfm.mit.edu:/pub/usenet/news.answers/standards-faq. ------------------------------------------------------------------------------ Subject: [12] I need source for the winners of the Dr Dobbs compression contest The source of the top 6 programs of the Feb 91 Dr Dobbs data compression contest are available by ftp on wsmr-simtel20.army.mil in pd1:ddjcompr.zip. [192.88.110.2] garbo.uwasa.fi:/pc/source/ddjcompr.zip [128.214.87.1] The sources are in MSDOS end-of-line format, one directory per program. Unix or VMS users, use "unzip -a ddjcompr" to get correct end-of-lines (add -d to recreate the directory structure if you are using an obsolete version of unzip such as 4.1). Three of the 6 programs are not portable and only run on MSDOS. compact and urban work on Unix, sixpack only requires minor modifications. ------------------------------------------------------------------------------ Subject: [13] I need source for arithmetic coding (See question 70 for an introduction to arithmetic coding.) The source for the arithmetic coder described in Chap.5 of Bell, Cleary, and Witten's book "Text Compression" (see question 7 above) (or, equivalently, in: Witten, Neal, and Cleary's article "Arithmetic Coding for data Compression" from Communications of the Association for Computing Machinery, 30 (6), pp.520-540, June, 1987) is available via anonymous ftp from fsa.cpsc.ucalgary.ca (136.159.2.1) in directory /pub/arithmetic.coding. It only comes with a simple order-0 model but it's set up so that adding your own more sophisticated one is straightforward. A low precisiè¡6Xref: nuchat comp.compression:7740 news.answers:9179 Path: nuchat!menudo.uh.edu!swrinde!cs.utexas.edu!utnut!torn!nott!bnrgate!bnr.co.uk!pipex!uknet!mcsun!julienas!chorus!chorus.fr From: jloup@chorus.fr (Jean-loup Gailly) Newsgroups: comp.compression,news.answers,comp.answers Subject: comp.compression Frequently Asked Questions (part 1/3) Summary: *** READ THIS BEFORE POSTING *** Keywords: data compression, FAQ Message-ID: Date: 9 Jun 93 13:23:27 GMT Expires: 30 Jul 93 16:17:20 GMT Sender: news@chorus.chorus.fr Reply-To: jloup@chorus.fr Followup-To: comp.compression Lines: 2399 Approved: news-answers-request@MIT.Edu Supersedes: . ------------------------------------------------------------------------------ Subject: [15] Where can I get image compression programs? JPEG: Source code for most any machine: ftp.uu.net:/graphics/jpeg/jpegsrc.v4.tar.Z [137.39.1.9] nic.funet.fi:/pub/graphics/packages/jpeg/jpegsrc.v4.tar.Z [128.214.6.100] Contact: jpeg-info@uunet.uu.net (Independent JPEG Group) havefun.stanford.edu:pub/jpeg/JPEGv1.0.tar.Z Contact: Andy Hung (see item 20 below) xv, an image viewer which can read JPEG pictures, is available in export.lcs.mit.edu: contrib/xv-2.21.tar.Z [18.24.0.12] MPEG: havefun.stanford.edu:/pub/mpeg/MPEGv1.1.tar.Z Contact: Andy Hung (see item 20 below) toe.cs.berkeley.edu:/pub/multimedia/mpeg/mpeg_play-2.0.tar.Z Contact: mpeg-bugs@cs.berkeley.edu nvr.com:/pub/NVR-software/Product-1.0.4.tar.Z (192.82.231.50) (free demo copy of NVR's software toolkit for SPARCstations) Contact: Todd Brunhoff H.261(P*64): havefun.stanford.edu:pub/p64/P64v1.1.tar.Z Contact: Andy Hung (see item 20 below) epic: (pyramid wavelet coder, see item 72) whitechapel.media.mit.edu:/pub/epic.tar.Z [18.85.0.125] Contact: Eero P. Simoncelli The "Lenna" test image is available as part of the EPIC package, where it is named "test_image". hcompress: (wavelet impage compression) stsci.edu:/software/hcompress/hcompress.tar.Z compfits: uwila.cfht.hawaii.edu:/pub/compfits/compfits.tar.Z [128.171.80.50] Contact: Jim Wright fitspress: cfata4.harvard.edu:/pub/fitspress08.tar.Z [128.103.40.79] tiff: For source and sample images, see question 18 below. ivs: Inria videoconference system ftp.inria.fr:/INRIA/ivs-2.1.tar.Z For image compression hardware, see item 85 in part 3 of this FAQ. ------------------------------------------------------------------------------ Subject: [16] What is the state of the art in lossless image compression? The current state-of-the-art is the JBIG algorithm. For an introduction to JBIG, see question 74 in part 2. JBIG works best on bi-level images (like faxes) and also works well on Gray-coded grey scale images up to about six or so bits per pixel. You just apply JBIG to the bit planes individually. For more bits/pixel, lossless JPEG provides better performance, sometimes. (For JPEG, see question 19 below.) You can find a description of JBIG in ISO/IEC CD 11544, contained in document ISO/IEC JTC1/SC2/N2285. The only way to get it is to ask your National Standards Body for a copy. In the USA, call ANSI at (212) 642-4900. ------------------------------------------------------------------------------ Subject: [17] What is the state of fractal compression? from Tal Kubo : According to Barnsley's book 'Fractals Everywhere', this method is based on a measure of deviation between a given image and its approximation by an IFS code. The Collage Theorem states that there is a convergent process to minimize this deviation. Unfortunately, according to an article Barnsley wrote for BYTE a few years ago, this convergence was rather slow, about 100 hours on a Cray, unless assisted by a person. Barnsley et al are not divulging any technical information beyond the meager bit in 'Fractals Everywhere'. The book explains the idea of IFS codes at length, but is vague about the application of the Collage theorem to specific compression problems. There is reason to believe that Barnsley's company has *no algorithm* which takes a given reasonable image and achieves the compression ratios initially claimed for their fractal methods. The 1000-to-1 compression advertised was achieved only for a 'rigged' class of images, with human assistance. The best unaided performance I've heard of is good lossy compression of about 80-1. Steve Tate confirms: Compression ratios (unzoomed) seem to range from 20:1 to 60:1... The quality is considerably worse than wavelets or JPEG on most of the non-contrived images I have seen. But Yuval Fisher disagrees: Their performance has improved dramatically beyond what they were talking about in BYTE a few years ago. Human assistance to the compression is no longer needed and the compression time is reasonable, although the more time and compute power you throw at the compression, the smaller the resulting file for the same level of quality. Geoffrey A Stephenson adds: Iterated systems are shipping a general purpose compressor at about 300 Pounds in the UK that claims "640x480 24 bit colour compression of about 1 min at 922k -> 10k on a 486/50 software only, decomp. to 8 bits in 3 secs, etc." At a recent multimedia conference in London they handed out free demo disks that show the decomp. in action. The package runs under both DOS anf WIN (DLLs provided for use in applications). They also sell a board to speed up compression and offer versions supporting full motion video (but not apparently at all SVGA sizes like the static picture version). I have not yet got my hands on a full version to test different types of pictures, but friends have a and claim it looks good. Programs: A fractal image compression program is available by ftp in lyapunov.ucsd.edu:/pub/young-fractal/unifs10.zip. (Unix users, See item 2 above for unzip on Unix.) Note the file size before you ftp it: 1.2 MB. The package contains source for compression and decompression, source for X-windows decompression, MSDOS executables and images. A newer version of the program is in yuvpak20.zip. A fractal image decompression program (note: decompression only) is available in /pub/inls-ucsd/fractal-2.0.tar on on the same ftp site (lyapunov.ucsd.edu). Note the file size before you ftp it: 1.3 MB. This file also contains a paper by Yuval Fisher (see reference below), and some executables and sample images. Reading this paper is required to understand how the Young compression programs (see above) works. References: A. Jacquin, 'Fractal image coding based on a theory of iterated contractive image transformations', Visual Comm. and Image Processing, vol SPIE-1360, 1990. (The best paper that explains the concept in a simple way.) A. Jacquin, "A Fractal Theory of Iterated Markov Operators with Applications to Digital Image Coding", PhD Thesis, Georgia Tech, 1989. It can be obtained from university microfilms for $35, phone 1-800-521-0600. M. Barnsley, L. Anson, "Graphics Compression Technology, SunWorld, October 1991, pp. 42-52. M.F. Barnsley, A. Jacquin, F. Malassenet, L. Reuter & A.D. Sloan, 'Harnessing chaos for image synthesis', Computer Graphics, vol 22 no 4 pp 131-140, 1988. M.F. Barnsley, A.E. Jacquin, 'Application of recurrent iterated function systems to images', Visual Comm. and Image Processing, vol SPIE-1001, 1988. A. Jacquin, "Image Coding Based on a Fractal Theory of Iterated Contractive Image Transformations" p.18, January 1992 (Vol 1 Issue 1) of IEEE Trans on Image Processing. A.E. Jacquin, 'A novel fractal block-coding technique for digital images', Proc. ICASSP 1990. G.E. Oien, S. Lepsoy & T.A. Ramstad, 'An inner product space approach to image coding by contractive transformations', Proc. ICASSP 1991, pp 2773-2776. D.S. Mazel, Fractal Modeling of Time-Series Data, PhD Thesis, Georgia Tech, 1991. (One dimensional, not pictures) S. A. Hollatz, "Digital image compression with two-dimensional affine fractal interpolation functions", Department of Mathematics and Statistics, University of Minnesota-Duluth, Technical Report 91-2. (a nuts-and-bolts how-to-do-it paper on the technique) Stark, J., "Iterated function systems as neural networks", Neural Networks, Vol 4, pp 679-690, Pergamon Press, 1991. Monro D M and Dudbridge F, "Fractal block coding of images", Electronics Letters 28(11):1053-1054 (1992) Beaumont J M, "Image data compression using fractal techniques", British Telecom Technological Journal 9(4):93-108 (1991) Fisher Y, "Fractal image compression", Siggraph 92 Graf S, "Barnsley's Scheme for the Fractal Encoding of Images", Journal Of Complexity, V8, 72-78 (1992). Books: The Fractal Transform, Michael F. Barnsley and Louisa F. Anson ISBN 0-86720-218-1, ca. 250 pp, $49.95 Fractal Image Compression Michael F. Barnsley and Lyman P. Hurd ISBN 0-86720-457-5, ca. 250 pp., $49.95 Copies can be ordered directly from the publisher by sending a message to kpeters@math.harvard.edu with name, address and a Mastercard or Visa card number with expiration date. Barnsley's company is: Iterated Systems, Inc. 5550A Peachtree Parkway, Suite 650 Norcross, GA 30092 tel: 404-840-0310 or 1-800-4FRACTL fax: 404-840-0806 ------------------------------------------------------------------------------ Subject: [18] I need specs and source for TIFF and CCITT group 4 Fax Specs for Group 3 and 4 image coding (group 3 is very similar to group 4) are in CCITT (1988) volume VII fascicle VII.3. They are recommendations T.4 and T.6 respectively. There is also an updated spec contained in 1992 recommendations T.1 to T.6. CCITT specs are available by anonymous ftp (see above answer on V.42bis). The T.4 and T.6 specs are in the directory /computing/ccitt/standards/ccitt/1988/ascii, files 7_3_01.txt.Z and 7_3_02.txt.Z respectively. The following paper covers T.4, T.6 and JBIG: "Review of standards for electronic imaging for facsimile systems" in Journal of Electronic Imaging, Vol. 1, No. 1, pp. 5-21, January 1992. Source code can be obtained as part of a TIFF toolkit - TIFF image compression techniques for binary images include CCITT T.4 and T.6: sgi.com:/graphics/tiff/v3.2.tar.Z [192.48.153.1] Contact: sam@sgi.com There is also a companion compressed tar file (v3.0pics.tar.Z) that has sample TIFF image files. A draft of TIFF 6.0 is in TIFF6.ps.Z. Concerning JPEG compression in TIFF 6.0, Tom Lane adds: The TIFF document won't do you much good unless you also have the official JPEG standard. That, you have to buy from ANSI or your national ISO member organization (DIN over there, I suppose). Worse, the TIFF 6.0 spec has a number of serious problems in its JPEG features. A clarification note will probably be needed to ensure that TIFF JPEG files are compatible across different implementations. I can't in good faith recommend that anyone use TIFF-JPEG until these problems are resolved. Software for reading and writing CCITT Group 3 and 4 images is also available in directory merry.cs.monash.edu.au:/pub/alanf/TIFF_FAX (130.194.67.101). Contact: Alan Finlay . See also question 54 below. ------------------------------------------------------------------------------ Subject: [19] What is JPEG? JPEG (pronounced "jay-peg") is a standardized image compression mechanism. JPEG stands for Joint Photographic Experts Group, the original name of the committee that wrote the standard. JPEG is designed for compressing either full-color or gray-scale digital images of "natural", real-world scenes. It does not work so well on non-realistic images, such as cartoons or line drawings. JPEG does not handle black-and-white (1-bit-per-pixel) images, nor does it handle motion picture compression. Standards for compressing those types of images are being worked on by other committees, named JBIG and MPEG respectively. Regular JPEG is "lossy", meaning that the image you get out of decompression isn't quite identical to what you originally put in. The algorithm achieves much of its compression by exploiting known limitations of the human eye, notably the fact that small color details aren't perceived as well as small details of light-and-dark. Thus, JPEG is intended for compressing images that will be looked at by humans. If you plan to machine-analyze your images, the small errors introduced by JPEG may be a problem for you, even if they are invisible to the eye. The JPEG standard includes a separate lossless mode, but it is not widely used and does not give nearly as much compression as the lossy mode. Question 75 "Introduction to JPEG" (in part 2 of this FAQ) gives an overview of how JPEG works and provides references for further reading. Also see the JPEG FAQ article, which covers JPEG software and usage hints. The JPEG FAQ is posted regularly in news.answers by Tom Lane . (See question 53 "Where are FAQ lists archived" if this posting has expired at your site.) For JPEG hardware, see item 85 in part 3 of this FAQ. ------------------------------------------------------------------------------ Subject: [20] I am looking for source of an H.261 codec and MPEG The H.261 spec is available on src.doc.ic.ac.uk in /computing/ccitt/standards/ccitt/1992/h/h261.doc.Z (or h261.rtf.Z). For H.261 hardware, see item 85 in part 3 of this FAQ. from Thierry TURLETTI : We have implemented a software version of H.261 codec. It runs on top of UNIX and X-Windows. The coder uses the simple video capture board "VideoPix" provided by SUN for the SparcStation. The output is directed towards a standard TCP connection, instead of the leased lines or switched circuits for which regular H.261 codecs are designed. This enable us to test video conferences over regular internet connections. We have to polish it a bit, but the first release is now available by anonymous ftp from avahi.inria.fr, in "/pub/h261.tar.Z". from Andy Hung : Public domain UNIX C source code to do both image and image sequence compression and decompression is available by anonymous ftp: MPEG-I havefun.stanford.edu:pub/mpeg/MPEGv1.1.tar.Z CCITT H.261(P*64) havefun.stanford.edu:pub/p64/P64v1.1.tar.Z JPEG havefun.stanford.edu:pub/jpeg/JPEGv1.1.tar.Z These codecs operate on raw raster scanned images. A software program to display raw raster-scanned YUV images and image sequences on X grayscale or color monitors is provided by a program in the anonymous ftp directory havefun.stanford.edu pub/cv/CVv1.1.tar.Z. If you are using the codecs above, we recommend that you ftp this file over as well. The source code has been compiled on DEC and SUN workstations. Caution: the P64 codec has not been tested compliant (any available p64 video streams would be much appreciated - please let us know at achung@cs.stanford.edu). The other codecs have been tested with streams from other encoders. We also have some IPB MPEG-I video coded streams in pub/mpeg/*.mpg; and P64 video streams in pub/p64/*.p64 that we have generated using our codecs. For a more complete description see the file havefun.stanford.edu:pub/README. ------------------------------------------------------------------------------ Subject: [25] Fast DCT (Discrete Cosine Transform) algorithms Many image compression methods, including the JPEG, MPEG, and H.261 standards, are based on the discrete cosine transform. A good overall introduction to DCT is the book "Discrete Cosine Transform---Algorithms, Advantages, Applications" by K.R. Rao and P. Yip (Academic Press, London, 1990). This has an extensive, though already dated, bibliography. Here are some newer references provided by Tom Lane . Most of these are in IEEE journals or conference proceedings, notably ICASSP = IEEE Intl. Conf. on Acoustics, Speech, and Signal Processing. ICCAS = IEEE Intl. Conf. on Circuits and Systems. DCC = Data Compression Conference. Polynomial Transform Computation of the 2-D DCT, Duhamel & Guillemot, ICASSP '90 p. 1515. A Forward-Mapping Realization of the Inverse DCT, McMillan & Westover, DCC '92 p. 219. A Fast Algorithm for 2-D DCT, Cho, Yun & Lee, ICASSP '91 p. 2197. Fast Algorithm and Implementation of 2-D DCT, Cho & Lee, Tr. CAS v38 p. 297. A DCT Chip based on a new Structured and Computationally Efficient DCT Algorithm, Duhamel, Guillemot & Carlach, ICCAS '90 p. 77. Trade-offs in the Computation of Mono- and Multi-dimensional DCTs, Vetterli, Duhamel & Guillemot, ICASSP '89 p. 999. Practical Fast 1-D DCT Algorithms with 11 Multiplications, Loeffler, Ligtenberg & Moschytz, ICASSP '89 p. 988. New Scaled DCT Algorithms for Fused Multiply/Add Architectures, Linzer & Feig, ICASSP '91 p. 2201. Fast Algorithms for the 2-D Discrete Cosine Transform, Kamangar & Rao, IEEE Tr. Computers, v C-31 p. 899. Fast 2-D Discrete Cosine Transform, Vetterli, ICASSP '85 p. 1538. A Two-Dimensional Fast Cosine Transform, Haque, Tr. ASSP v ASSP-33 p. 1532. Real-Time Parallel and Fully Pipelined 2-D DCT Lattice Structures with Application to HDTV Systems, Chiu & Liu, Tr. CAS for Video Tech, v 2 p. 25. The free JPEG code (jpegsrc.v4.tar.Z) has one of the fastest implementations of the DCT code. It's all in the files jfwddct.c and jrevdct.c (which do the dct and idct, respectively). See item 15 for ftp locations. ------------------------------------------------------------------------------ Subject: [26] Are there algorithms and standards for audio compression? Yes. See the introduction to MPEG given in part 2 of this FAQ. A lossless compressor for 8bit and 16bit audio data (.au) is available by anonymous ftp at svr-ftp.eng.cam.ac.uk:/pub/misc/shorten-1.03.shar. It works by using Huffman coding of prediction residuals. Compression is generally better than that obtained by applying general purpose compression utilities to audio files. Copied from the comp.dsp FAQ posted by guido@cwi.nl (Guido van Rossum): Strange though it seems, audio data is remarkably hard to compress effectively. For 8-bit data, a Huffman encoding of the deltas between successive samples is relatively successful. For 16-bit data, companies like Sony and Philips have spent millions to develop proprietary schemes. Public standards for voice compression are slowly gaining popularity, e.g. CCITT G.721 and G.723 (ADPCM at 32 and 24 kbits/sec). (ADPCM == Adaptive Delta Pulse Code Modulation.) Free source code for a *fast* 32 kbits/sec ADPCM (lossy) algorithm is available by ftp from ftp.cwi.nl as /pub/adpcm.shar. (** NOTE: if you are using v1.0, you should get v1.1, released 17-Dec-1992, which fixes a serious bug -- the quality of v1.1 is claimed to be better than uLAW **) (Note that U-LAW and silence detection can also be considered compression schemes.) A note on u-law from Markus Kuhn : u-law (more precisely (greek mu)-law or 5-law if you have an 8-bit ISO terminal) is more an encoding then a compression method, although a 12 to 8 bit reduction is normally part of the encoding. The official definition is CCITT recommendation G.711. If you want to know how to get CCITT documents, check the Standards FAQ posted to news.answers or get the file standards-faq by ftp in directory rtfm.mit.edu:/pub/usenet/news.answers. See also the comp.dsp FAQ for more information on: - The U.S. DoD's Federal-Standard-1016 based 4800 bps code excited linear prediction voice coder version 3.2 (CELP 3.2) - The U.S. DoD's Federal-Standard-1015/NATO-STANAG-4198 based 2400 bps linear prediction coder version 53 (LPC-10e v53) - Realtime DSP code and hardware for FS-1015 and FS-1016 You can find the comp.dsp FAQ in comp.dsp or news.answers with subject: "FAQ: Audio File Formats" or by ftp on rtfm.mit.edu in /pub/usenet/news.answers/audio-fmts/part1. CELP C code for Sun SPARCs is available for anonymous ftp at furmint.nectar.cs.cmu.edu, in directory celp.audio.compression. Recommended reading: Digital Coding of Waveforms: Principles and Applications to Speech and Video. N. S. Jayant and Peter Noll. Prentice-Hall, 1984, ISBN 0-13-211913-7. from Markus Kuhn : One highest quality sound compression format is called ASPEC and has been developped by a team at the Frauenhofer Institut in Erlangen (Germany) and others. ASPEC produces CD like quality and offers several bitrates, one is 128 kbit/s. It is a lossy algorithm that throws away frequencys that aren't registered in the human cochlea in addition to sophisticated entropy coding. The 64 kbit/s ASPEC variant might soon bring hifi quality ISDN phone connections. It has been implemented on standard DSPs. The Layer 3 MPEG audio compression standard now contains what is officially called the best parts of the ASPEC and MUSICAM algorithms. A reference is: K.Brandenburg, G.Stoll, Y.F.Dehery, J.D.Johnston, L.v.d.Kerkhof, E.F.Schroeder: "The ISO/MPEG-Audio Codec: A Generic Standard for Coding of High Quality Digital Audio", 92nd. AES-convention, Vienna 1992, preprint 3336 from Jutta Degener and Carsten Bormann : GSM 06.10 13 kbit/s RPE/LTP speech compression available -------------------------------------------------------- The Communications and Operating Systems Research Group (KBS) at the Technische Universitaet Berlin is currently working on a set of UNIX-based tools for computer-mediated telecooperation that will be made freely available. As part of this effort we are publishing an implementation of the European GSM 06.10 provisional standard for full-rate speech transcoding, prI-ETS 300 036, which uses RPE/LTP (residual pulse excitation/long term prediction) coding at 13 kbit/s. GSM 06.10 compresses frames of 160 13-bit samples (8 kHz sampling rate, i.e. a frame rate of 50 Hz) into 260 bits; for compatibility with typical UNIX applications, our implementation turns frames of 160 16-bit linear samples into 33-byte frames (1650 Bytes/s). The quality of the algorithm is good enough for reliable speaker recognition; even music often survives transcoding in recognizable form (given the bandwidth limitations of 8 kHz sampling rate). Version 1.0 of the implementation is available per anonymous ftp from tub.cs.tu-berlin.de as /pub/tubmik/gsm-1.0.tar.Z. Questions and bug reports should be directed to toast@tub.cs.tu-berlin.de. Note that the distribution is not available via E-mail (please use one of the ftp-via-E-mail servers). from Bob Kimball : I work for Qualcomm Inc. and we are designing a digital cellular telephone system. Our phone uses our variable rate vocoder (QCELP) which is designed for speach and compresses 64Kb/s speach to 8Kb/s through 1Kb/s with 8Kb/s being full rate and 1Kb/s for 1/8 rate speach. It works great for speach. The QCELP process is documented in our Common Air Interface (CAI) which is available for anonymous ftp from lorien.qualcomm.com in /pub/cdma each chapter is a postscript file. The vocoder is described in appendix A. The whole document is quite large. This is the document which is currently going through the TIA standard committee so it is not a final version. The appendix on the vocoder should be almost identical to the final version... whenever that comes out. from Nicola Ferioli : On wsmr-simtel20.army.mil, pd1: VOCPAK10.ZIP Lossless 8-bit sound file compressor VOCPACK is a compressor/decompressor for 8-bit digital sound using a lossless algorithm; it is useful to save disk space without degrading sound quality. It can compress signed and unsigned data, sampled at any rate, mono or stereo. Since the method used is not lossy, it isn't necessary to strip file headers before compressing. VOCPACK was developed for use with .VOC (SoundBlaster) and .WAV (Windows) files, but any 8-bit sound can be compressed since the program takes no assumptions about the file structure. The typical compression ratio obtained goes from 0,8 for files sampled at 11 KHz to 0,4 for 44 Khz files. The best results are obtained with 44 KHz sounds (mono or stereo): general-purpose archivers create files that can be twice longer than the output of VOCPACK. You can obtain smaller values using lossy compressors but if your goal is to keep the sound quality unaltered you should use a lossless program like VOCPACK. ------------------------------------------------------------------------------ Subject: [30] My archive is corrupted! The two most common reasons for this are (1) failing to use the magic word "tenex" (when connected to SIMTEL20 and other TOPS20 systems) or "binary" (when connected to UNIX systems) when transferring the file from an ftp site to your host machine. The reasons for this are technical and boring. A synonym for "tenex" is "type L 8", in case your ftp doesn't know what "tenex" means. (2) failing to use an eight-bit binary transfer protocol when transferring the file from the host to your PC. Make sure to set the transfer type to "binary" on both your host machine and your PC. ------------------------------------------------------------------------------ Subject: [31] pkunzip reports a CRC error! The portable zip 1.1 contains many workarounds for undocumented restrictions in pkunzip. Compatibility is ensured for pkunzip 1.10 only. All previous versions (pkunzip 1.0x) have too many bugs and cannot be supported. This includes Borland unzip. So if your pkunzip reports a CRC error, check that you are not using an obsolete version. Get either pkzip 2.04g or unzip 5.0p1 (see question 2 above for ftp sites). To generate zip files compatible with pkunzip 1.10, use zip 1.1 (see item 2 above for ftp site). ------------------------------------------------------------------------------ Subject: [32] VMS zip is not compatible with pkzip! The problem is most likely in the file transfer program. Many use kermit to transfer zipped files between PC and VMS VAX. The following VMS kermit settings make VMS-ZIP compatible with PKZIP: VMS kermit PC kermit --------------- -------------- Uploading PKZIPped file to be UNZIPped: set fi ty fixed set fi ty bi Downloading ZIPped file to be PKUNZIPped: set fi ty block set fi ty bi If you are not using kermit, transfer a file created by pkzip on MSDOS to VMS, transfer it back to your PC and check that pkunzip can extract it. ------------------------------------------------------------------------------ Subject: [33] I have a problem with Stacker! The newsgroup comp.compression is *not* the appropriate place to discuss about one specific program on one specific operating system. Since you have bought a legal copy of Stacker, you have the documentation of your product; please read it. If you can't find the answer in the documentation, please report the problem to the Stac customer support. If you really feel that the net has to know about your problem, please post in one of the MSDOS newsgroups, such as comp.os.msdos.apps or comp.binaries.ibm.pc.d. ------------------------------------------------------------------------------ Subject: [50] What is this 'tar' compression program? tar is not a compression program. It just combines several files into one, without compressing them. tar file are often compressed with 'compress', resulting in a .tar.Z file. See question 2, file type .tar.Z. GNU tar has the capability to (de)compress files as well. When you have to archive a lot of very small files, it is often preferable to create a single .tar file and compress it, than to compress the individual files separately. The compression program can thus take advantage of redundancy between separate files. The disadvantage is that you must uncompress the whole .tar file to extract any member. ------------------------------------------------------------------------------ Subject: [51] I need a CRC algorithm As its name implies (Cyclic Redundancy Check) a crc adds redundancy whereas the topic of this group is to remove it. But since this question comes up often, here is some code (by Rob Warnock ). The following C code does CRC-32 in BigEndian/BigEndian byte/bit order. That is, the data is sent most significant byte first, and each of the bits within a byte is sent most significant bit first, as in FDDI. You will need to twiddle with it to do Ethernet CRC, i.e., BigEndian/LittleEndian byte/bit order. [Left as an exercise for the reader.] The CRCs this code generates agree with the vendor-supplied Verilog models of several of the popular FDDI "MAC" chips. u_long crc32_table[256]; /* Initialized first time "crc32()" is called. If you prefer, you can * statically initialize it at compile time. [Another exercise.] */ u_long crc32(u_char *buf, int len) { u_char *p; u_long crc; if (!crc32_table[1]) /* if not already done, */ init_crc32(); /* build table */ crc = 0xffffffff; /* preload shift register, per CRC-32 spec */ for (p = buf; len > 0; ++p, --len) crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p]; return ~crc; /* transmit complement, per CRC-32 spec */ } /* * Build auxiliary table for parallel byte-at-a-time CRC-32. */ #define CRC32_POLY 0x04c11db7 /* AUTODIN II, Ethernet, & FDDI */ init_crc32() { int i, j; u_long c; for (i = 0; i < 256; ++i) { for (c = i << 24, j = 8; j > 0; --j) c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1); crc32_table[i] = c; } } See also ftp.uni-erlangen.de:/pub/doc/ISO/english/async-HDLC, and the source of all archivers, such as the file makecrc.c in the sources of zip 1.9 (see item 2). ------------------------------------------------------------------------------ Subject: [52] What about those people who continue to ask frequently asked questions in spite of the frequently asked questions document? Just send them a polite mail message, referring them to this document. There is no need to flame them on comp.compression. That would just add more noise to this group. Posted answers that are in the FAQ are just as annoying as posted questions that are in the FAQ. ------------------------------------------------------------------------------ Subject: [53] Where are FAQ lists archived? Many are crossposted to news.answers. That newsgroup should have a long expiry time at your site; if not, talk to your sysadmin. FAQ lists are available by anonymous FTP from rtfm.mit.edu. The comp.compression FAQ that you are reading is in directory /pub/usenet/news.answers/compression-faq If you don't have FTP access, you can access the archives by mail server. Send an email message to mail-server@rtfm.mit.edu containing the commands send usenet/news.answers/compression-faq/part1 send usenet/news.answers/compression-faq/part2 send usenet/news.answers/compression-faq/part3 For instructions, send an email message to the same address with the words "help" and "index" (no quotes) on separate lines. If you don't get a reply, check your return address, or add a line such as path myname@foo.edu ------------------------------------------------------------------------------ Subject: [54] I need specs for graphics formats Have a look in directory /pub/graphics.formats on zamenhof.cs.rice.edu. It contains descriptions of gif, tiff, fits, etc... See also the FAQ list for comp.graphics. See item 53 for an ftp site. ------------------------------------------------------------------------------ Subject: [55] Where can I find Lenna and other images? A bunch of standard images (lenna, baboon, cameraman, crowd, moon etc..) are on ftp site eedsp.gatech.edu (130.207.226.2) in directory /database/images. The images are in 256-level grayshades (256x256 pixels, 256 "colors"). The site ipl.rpi.edu (128.113.14.50) has standard images in two directories: ipl.rpi.edu:/pub/image/still/usc ipl.rpi.edu:/pub/image/still/canon (The directory /pub/image/sequence has been taken offline because of possible copyright problems.) In each of those directories are the following directories: bgr - 24 bit blue, green, red color - 24 bit red, green, blue gray - 8 bit grayscale uniform weighted gray601 - 8 bit grayscale CCIR-601 weighted And in these directories are the actual images. For example, the popular lena image is in ipl.rpi.edu:/pub/image/still/usc/color/lena # 24 bit RGB ipl.rpi.edu:/pub/image/still/usc/bgr/lena # 24 bit BGR ipl.rpi.edu:/pub/image/still/usc/gray/lena # 8 bit gray All of the images are in Sun rasterfile format. You can use the pbm utilities to convert them to whatever format is most convenient. [pbm is available in ftp.ee.lbl.gov:/pbmplus*.tar.Z]. Questions about the ipl archive should be sent to help@ipl.rpi.edu. Rodney Peck is interested in some method of establishing a canonical ftp database of images but does not have the resources to provide an ftp site for that database. Send suggestions to rodney@balltown.cma.com. Beware: the same image often comes in many different forms, at different resolutions, etc... The original lenna image is 512 wide, 512 high, 8 bits per pel, red, green and blue fields. Gray-scale versions of Lenna have been obtained in two different ways from the original: (1) Using the green field as a gray-scale image, and (2) Doing an RGB->YUV transformation and saving the Y component. Method (1) makes it easier to compare different people's results since everyone's version should be the same using that method. Method (2) produces a more correct image. For the curious: 'lena' or 'lenna' is a digitized Playboy centerfold, from November 1972. (Lenna is the spelling in Playboy, Lena is the Swedish spelling of the name.) Lena Soderberg (ne Sjooblom) was last reported living in her native Sweden, happily married with three kids and a job with the state liquor monopoly. In 1988, she was interviewed by some Swedish computer related publication, and she was pleasantly amused by what had happened to her picture. That was the first she knew of the use of that picture in the computer business. The editorial in the January 1992 issue of Optical Engineering (v. 31 no. 1) details how Playboy has finally caught on to the fact that their copyright on Lenna Sjooblom's photo is being widely infringed. It sounds as if you will have to get permission from Playboy to publish it in the future. Note on the CCITT test images, by Robert Estes : The ccitt files are in ipl.rpi.edu:/image-archive/bitmap/ccitt (128.113.14.50). They are named ccitt-n.ras.Z where n goes from 1 to 8. Each file has an accompanying doc file called ccitt-n.ras.doc which describes the image file. Here's the doc file for ccitt-1.ras: Name ccitt-1.ras Size 1728 x 2376 x 1 Type 1 bit standard format sun rasterfile Keywords binary standard image 1 bit fax Description One of eight images from the standard binary CCITT test image set. This set is commonly used to compare binary image compression techniques. The images are are 1728x2376 pixels. ------------------------------------------------------------------------------ Subject: [56] I am looking for a message digest algorithm Look on the ftp site rsa.com, in directory /pub. MD4 and MD5 are there. This question would be more appropriate on sci.crypt. End of part 1 of the comp.compression faq. Archive-name: compression-faq/part2 Last-modified: Feb 9th, 1993 This file is part 2 of a set of Frequently Asked Questions for the groups comp.compression and comp.compression.research. If you did not get part 1 or 3, you can get them by ftp on rtfm.mit.edu in directory /pub/usenet/news.answers/compression-faq If you don't want to see this FAQ regularly, please add the subject line to your kill file. If you have corrections or suggestions for this FAQ, send them to Jean-loup Gailly . Thank you. Contents ======== Part 2: (Long) introductions to data compression techniques [70] Introduction to data compression (long) Huffman and Related Compression Techniques Arithmetic Coding Substitutional Compressors The LZ78 family of compressors The LZ77 family of compressors [71] Introduction to MPEG (long) What is MPEG? Does it have anything to do with JPEG? Then what's JBIG and MHEG? What has MPEG accomplished? So how does MPEG I work? What about the audio compression? So how much does it compress? What's phase II? When will all this be finished? How do I join MPEG? How do I get the documents, like the MPEG I draft? [72] What is wavelet theory? [73] What is the theoretical compression limit? [74] Introduction to JBIG [75] Introduction to JPEG Part 3: (Long) list of image compression hardware [85] Image compression hardware [99] Acknowledgments Search for "Subject: [#]" to get to question number # quickly. Some news readers can also take advantage of the message digest format used here. ------------------------------------------------------------------------------ Subject: [70] Introduction to data compression (long) Written by Peter Gutmann . Huffman and Related Compression Techniques ------------------------------------------ *Huffman compression* is a statistical data compression technique which gives a reduction in the average code length used to represent the symbols of a alphabet. The Huffman code is an example of a code which is optimal in the case where all symbols probabilities are integral powers of 1/2. A Huffman code can be built in the following manner: (1) Rank all symbols in order of probability of occurrence. (2) Successively combine the two symbols of the lowest probability to form a new composite symbol; eventually we will build a binary tree where each node is the probability of all nodes beneath it. (3) Trace a path to each leaf, noticing the direction at each node. For a given frequency distribution, there are many possible Huffman codes, but the total compressed length will be the same. It is possible to define a 'canonical' Huffman tree, that is, pick one of these alternative trees. Such a canonical tree can then be represented very compactly, by transmitting only the bit length of each code. This technique is used in most archivers (pkzip, lha, zoo, arj, ...). A technique related to Huffman coding is *Shannon-Fano coding*, which was suggested by Shannon and Weaver in 1949 and modified by Fano in 1961. It works as follows: (1) Divide the set of symbols into two equal or almost equal subsets based on the probability of occurrence of characters in each subset. The first subset is assigned a binary zero, the second a binary one. (2) Repeat step (1) until all subsets have a single element. The algorithm used to create the Huffman codes is bottom-up, and the one for the Shannon-Fano codes is top-down. Huffman encoding always generates optimal codes, Shannon-Fano sometimes uses a few more bits. Arithmetic Coding ----------------- It would appear that Huffman or Shannon-Fano coding is the perfect means of compressing data. However, this is *not* the case. As mentioned above, these coding methods are optimal when and only when the symbol probabilities are integral powers of 1/2, which is usually not the case. The technique of *arithmetic coding* does not have this restriction: It achieves the same effect as treating the message as one single unit (a technique which would, for Huffman coding, require enumeration of every single possible message), and thus attains the theoretical entropy bound to compression efficiency for any source. Arithmetic coding works by representing a number by an interval of real numbers between 0 and 1. As the message becomes longer, the interval needed to represent it becomes smaller and smaller, and the number of bits needed to specify that interval increases. Successive symbols in the message reduce this interval in accordance with the probability of that symbol. The more likely symbols reduce the range by less, and thus add fewer bits to the message. 1 Codewords +-----------+-----------+-----------+ /-----\ | |8/9 YY | Detail |<- 31/32 .11111 | +-----------+-----------+<- 15/16 .1111 | Y | | too small |<- 14/16 .1110 |2/3 | YX | for text |<- 6/8 .110 +-----------+-----------+-----------+ | | |16/27 XYY |<- 10/16 .1010 | | +-----------+ | | XY | | | | | XYX |<- 4/8 .100 | |4/9 | | | +-----------+-----------+ | | | | | X | | XXY |<- 3/8 .011 | | |8/27 | | | +-----------+ | | XX | | | | | |<- 1/4 .01 | | | XXX | | | | | |0 | | | +-----------+-----------+-----------+ As an example of arithmetic coding, lets consider the example of two symbols X and Y, of probabilities 0.66 and 0.33. To encode this message, we examine the first symbol: If it is a X, we choose the lower partition; if it is a Y, we choose the upper partition. Continuing in this manner for three symbols, we get the codewords shown to the right of the diagram above - they can be found by simply taking an appropriate location in the interval for that particular set of symbols and turning it into a binary fraction. In practice, it is also necessary to add a special end-of-data symbol, which is not represented in this simpe example. In this case the arithmetic code is not completely efficient, which is due to the shortness of the message - with longer messages the coding efficiency does indeed approach 100%. Now that we have an efficient encoding technique, what can we do with it? What we need is a technique for building a model of the data which we can then use with the encoder. The simplest model is a fixed one, for example a table of standard letter frequencies for English text which we can then use to get letter probabilities. An improvement on this technique is to use an *adaptive model*, in other words a model which adjusts itself to the data which is being compressed as the data is compressed. We can convert the fixed model into an adaptive one by adjusting the symbol frequencies after each new symbol is encoded, allowing the model to track the data being transmitted. However, we can do much better than that. Using the symbol probabilities by themselves is not a particularly good estimate of the true entropy of the data: We can take into account intersymbol probabilities as well. The best compressors available today take this approach: DMC (Dynamic Markov Coding) starts with a zero-order Markov model and gradually extends this initial model as compression progresses; PPM (Prediction by Partial Matching) looks for a match of the text to be compressed in an order-n context. If no match is found, it drops to an order n-1 context, until it reaches order 0. Both these techniques thus obtain a much better model of the data to be compressed, which, combined with the use of arithmetic coding, results in superior compression performance. So if arithmetic coding-based compressors are so powerful, why are they not used universally? Apart from the fact that they are relatively new and haven't come into general use too much yet, there is also one major concern: The fact that they consume rather large amounts of computing resources, both in terms of CPU power and memory. The building of sophisticated models for the compression can chew through a fair amount of memory (especially in the case of DMC, where the model can grow without bounds); and the arithmetic coding itself involves a fair amount of number crunching. There is however an alternative approach, a class of compressors generally referred to as *substitutional* or *dictionary-based compressors*. Substitutional Compressors -------------------------- The basic idea behind a substitutional compressor is to replace an occurrence of a particular phrase or group of bytes in a piece of data with a reference to a previous occurrence of that phrase. There are two main classes of schemes, named after Jakob Ziv and Abraham Lempel, who first proposed them in 1977 and 1978. LZ78-based schemes work by entering phrases into a *dictionary* and then, when a repeat occurrence of that particular phrase is found, outputting the dictionary index instead of the phrase. There exist several compression algorithms based on this principle, differing mainly in the manner in which they manage the dictionary. The most well-known scheme (in fact the most well-known of all the Lempel-Ziv compressors, the one which is generally (and mistakenly) referred to as "Lempel-Ziv Compression"), is Terry Welch's LZW scheme, which he designed in 1984 for implementation in hardware for high- performance disk controllers. Input string: /WED/WE/WEE/WEB Character input: Code output: New code value and associated string: /W / 256 = /W E W 257 = WE D E 258 = ED / D 259 = D/ WE 256 260 = /WE / E 261 = E/ WEE 260 262 = /WEE /W 261 263 = E/W EB 257 264 = WEB B LZW starts with a 4K dictionary, of which entries 0-255 refer to individual bytes, and entries 256-4095 refer to substrings. Each time a new code is generated it means a new string has been parsed. New strings are generated by appending the current character K to the end of an existing string w. The algorithm for LZW compression is as follows: set w = NIL loop read a character K if wK exists is in the dictionary w = wK else output the code for w add wK to the string table w = K endloop A sample run of LZW over a (highly redundant) input string can be seen in the diagram above. The strings are built up character-by-character starting with a code value of 256. LZW decompression takes the stream of codes and uses it to exactly recreate the original input data. Just like the compression algorithm, the decompressor adds a new string to the dictionary each time it reads in a new code. All it needs to do in addition is to translate each incoming code into a string and send it to the output. A sample run of the LZW decompressor is shown in below. Input code: /WED<256>E<260><261><257>B Input code: Output string: New code value and associated string: / / W W 256 = /W E E 257 = WE D D 258 = ED 256 /W 259 = D/ E E 260 = /WE 260 /WE 261 = E/ 261 E/ 262 = /WEE 257 WE 263 = E/W B B 264 = WEB The most remarkable feature of this type of compression is that the entire dictionary has been transmitted to the decoder without actually explicitly transmitting the dictionary. At the end of the run, the decoder will have a dictionary identical to the one the encoder has, built up entirely as part of the decoding process. LZW is more commonly encountered today in a variant known as LZC, after its use in the UNIX "compress" program. In this variant, pointers do not have a fixed length. Rather, they start with a length of 9 bits, and then slowly grow to their maximum possible length once all the pointers of a particular size have been used up. Furthermore, the dictionary is not frozen once it is full as for LZW - the program continually monitors compression performance, and once this starts decreasing the entire dictionary is discarded and rebuilt from scratch. More recent schemes use some sort of least-recently-used algorithm to discard little-used phrases once the dictionary becomes full rather than throwing away the entire dictionary. Finally, not all schemes build up the dictionary by adding a single new character to the end of the current phrase. An alternative technique is to concatenate the previous two phrases (LZMW), which results in a faster buildup of longer phrases than the character-by-character buildup of the other methods. The disadvantage of this method is that a more sophisticated data structure is needed to handle the dictionary. [A good introduction to LZW, MW, AP and Y coding is given in the yabba package. For ftp information, see question 2 in part one, file type .Y] LZ77-based schemes keep track of the last n bytes of data seen, and when a phrase is encountered that has already been seen, they output a pair of values corresponding to the position of the phrase in the previously-seen buffer of data, and the length of the phrase. In effect the compressor moves a fixed-size *window* over the data (generally referred to as a *sliding window*), with the position part of the (position, length) pair referring to the position of the phrase within the window. The most commonly used algorithms are derived from the LZSS scheme described by James Storer and Thomas Szymanski in 1982. In this the compressor maintains a window of size N bytes and a *lookahead buffer* the contents of which it tries to find a match for in the window: while( lookAheadBuffer not empty ) { get a pointer ( position, match ) to the longest match in the window for the lookahead buffer; if( length > MINIMUM_MATCH_LENGTH ) { output a ( position, length ) pair; shift the window length characters along; } else { output the first character in the lookahead buffer; shift the window 1 character along; } } Decompression is simple and fast: Whenever a ( position, length ) pair is encountered, go to that ( position ) in the window and copy ( length ) bytes to the output. Sliding-window-based schemes can be simplified by numbering the input text characters mod N, in effect creating a circular buffer. The sliding window approach automatically creates the LRU effect which must be done explicitly in LZ78 schemes. Variants of this method apply additional compression to the output of the LZSS compressor, which include a simple variable-length code (LZB), dynamic Huffman coding (LZH), and Shannon-Fano coding (ZIP 1.x)), all of which result in a certain degree of improvement over the basic scheme, especially when the data are rather random and the LZSS compressor has little effect. Recently an algorithm was developed which combines the ideas behind LZ77 and LZ78 to produce a hybrid called LZFG. LZFG uses the standard sliding window, but stores the data in a modified trie data structure and produces as output the position of the text in the trie. Since LZFG only inserts complete *phrases* into the dictionary, it should run faster than other LZ77-based compressors. All popular archivers (arj, lha, zip, zoo) are variations on the LZ77 theme. ------------------------------------------------------------------------------ Subject: [71] Introduction to MPEG (long) For MPEG players, see item 15 in part 1 of the FAQ. Frank Gadegast also posts a FAQ specialized in MPEG. Introduction written by Mark Adler around January 1992 (and hence wildly out of date in this fast moving area--any volunteers to update this section are welcome): Q. What is MPEG? A. MPEG is a group of people that meet under ISO (the International Standards Organization) to generate standards for digital video (sequences of images in time) and audio compression. In particular, they define a compressed bit stream, which implicitly defines a decompressor. However, the compression algorithms are up to the individual manufacturers, and that is where proprietary advantage is obtained within the scope of a publicly available international standard. MPEG meets roughly four times a year for roughly a week each time. In between meetings, a great deal of work is done by the members, so it doesn't all happen at the meetings. The work is organized and planned at the meetings. Q. So what does MPEG stand for? A. Moving Pictures Experts Group. Q. Does it have anything to do with JPEG? A. Well, it sounds the same, and they are part of the same subcommittee of ISO along with JBIG and MHEG, and they usually meet at the same place at the same time. However, they are different sets of people with few or no common individual members, and they have different charters and requirements. JPEG is for still image compression. Q. Then what's JBIG and MHEG? A. Sorry I mentioned them. Ok, I'll simply say that JBIG is for binary image compression (like faxes), and MHEG is for multi-media data standards (like integrating stills, video, audio, text, etc.). For an introduction to JBIG, see question 74 below. Q. Ok, I'll stick to MPEG. What has MPEG accomplished? A. So far (as of January 1992), they have completed the "Committee Draft" of MPEG phase I, colloquially called MPEG I. It defines a bit stream for compressed video and audio optimized to fit into a bandwidth (data rate) of 1.5 Mbits/s. This rate is special because it is the data rate of (uncompressed) audio CD's and DAT's. The draft is in three parts, video, audio, and systems, where the last part gives the integration of the audio and video streams with the proper timestamping to allow synchronization of the two. They have also gotten well into MPEG phase II, whose task is to define a bitstream for video and audio coded at around 3 to 10 Mbits/s. Q. So how does MPEG I work? A. First off, it starts with a relatively low resolution video sequence (possibly decimated from the original) of about 352 by 240 frames by 30 frames/s (US--different numbers for Europe), but original high (CD) quality audio. The images are in color, but converted to YUV space, and the two chrominance channels (U and V) are decimated further to 176 by 120 pixels. It turns out that you can get away with a lot less resolution in those channels and not notice it, at least in "natural" (not computer generated) images. The basic scheme is to predict motion from frame to frame in the temporal direction, and then to use DCT's (discrete cosine transforms) to organize the redundancy in the spatial directions. The DCT's are done on 8x8 blocks, and the motion prediction is done in the luminance (Y) channel on 16x16 blocks. In other words, given the 16x16 block in the current frame that you are trying to code, you look for a close match to that block in a previous or future frame (there are backward prediction modes where later frames are sent first to allow interpolating between frames). The DCT coefficients (of either the actual data, or the difference between this block and the close match) are "quantized", which means that you divide them by some value to drop bits off the bottom end. Hopefully, many of the coefficients will then end up being zero. The quantization can change for every "macroblock" (a macroblock is 16x16 of Y and the corresponding 8x8's in both U and V). The results of all of this, which include the DCT coefficients, the motion vectors, and the quantization parameters (and other stuff) is Huffman coded using fixed tables. The DCT coefficients have a special Huffman table that is "two-dimensional" in that one code specifies a run-length of zeros and the non-zero value that ended the run. Also, the motion vectors and the DC DCT components are DPCM (subtracted from the last one) coded. Q. So is each frame predicted from the last frame? A. No. The scheme is a little more complicated than that. There are three types of coded frames. There are "I" or intra frames. They are simply a frame coded as a still image, not using any past history. You have to start somewhere. Then there are "P" or predicted frames. They are predicted from the most recently reconstructed I or P frame. (I'm describing this from the point of view of the decompressor.) Each macroblock in a P frame can either come with a vector and difference DCT coefficients for a close match in the last I or P, or it can just be "intra" coded (like in the I frames) if there was no good match. Lastly, there are "B" or bidirectional frames. They are predicted from the closest two I or P frames, one in the past and one in the future. You search for matching blocks in those frames, and try three different things to see which works best. (Now I have the point of view of the compressor, just to confuse you.) You try using the forward vector, the backward vector, and you try averaging the two blocks from the future and past frames, and subtracting that from the block being coded. If none of those work well, you can intra- code the block. The sequence of decoded frames usually goes like: IBBPBBPBBPBBIBBPBBPB... Where there are 12 frames from I to I (for US and Japan anyway.) This is based on a random access requirement that you need a starting point at least once every 0.4 seconds or so. The ratio of P's to B's is based on experience. Of course, for the decoder to work, you have to send that first P *before* the first two B's, so the compressed data stream ends up looking like: 0xx312645... where those are frame numbers. xx might be nothing (if this is the true starting point), or it might be the B's of frames -2 and -1 if we're in the middle of the stream somewhere. You have to decode the I, then decode the P, keep both of those in memory, and then decode the two B's. You probably display the I while you're decoding the P, and display the B's as you're decoding them, and then display the P as you're decoding the next P, and so on. Q. You've got to be kidding. A. No, really! Q. Hmm. Where did they get 352x240? A. That derives from the CCIR-601 digital television standard which is used by professional digital video equipment. It is (in the US) 720 by 243 by 60 fields (not frames) per second, where the fields are interlaced when displayed. (It is important to note though that fields are actually acquired and displayed a 60th of a second apart.) The chrominance channels are 360 by 243 by 60 fields a second, again interlaced. This degree of chrominance decimation (2:1 in the horizontal direction) is called 4:2:2. The source input format for MPEG I, called SIF, is CCIR-601 decimated by 2:1 in the horizontal direction, 2:1 in the time direction, and an additional 2:1 in the chrominance vertical direction. And some lines are cut off to make sure things divide by 8 or 16 where needed. Q. What if I'm in Europe? A. For 50 Hz display standards (PAL, SECAM) change the number of lines in a field from 243 or 240 to 288, and change the display rate to 50 fields/s or 25 frames/s. Similarly, change the 120 lines in the decimated chrominance channels to 144 lines. Since 288*50 is exactly equal to 240*60, the two formats have the same source data rate. Q. You didn't mention anything about the audio compression. A. Oh, right. Well, I don't know as much about the audio compression. Basically they use very carefully developed psychoacoustic models derived from experiments with the best obtainable listeners to pick out pieces of the sound that you can't hear. There are what are called "masking" effects where, for example, a large component at one frequency will prevent you from hearing lower energy parts at nearby frequencies, where the relative energy vs. frequency that is masked is described by some empirical curve. There are similar temporal masking effects, as well as some more complicated interactions where a temporal effect can unmask a frequency, and vice-versa. The sound is broken up into spectral chunks with a hybrid scheme that combines sine transforms with subband transforms, and the psychoacoustic model written in terms of those chunks. Whatever can be removed or reduced in precision is, and the remainder is sent. It's a little more complicated than that, since the bits have to be allocated across the bands. And, of course, what is sent is entropy coded. Q. So how much does it compress? A. As I mentioned before, audio CD data rates are about 1.5 Mbits/s. You can compress the same stereo program down to 256 Kbits/s with no loss in discernable quality. (So they say. For the most part it's true, but every once in a while a weird thing might happen that you'll notice. However the effect is very small, and it takes a listener trained to notice these particular types of effects.) That's about 6:1 compression. So, a CD MPEG I stream would have about 1.25 MBits/s left for video. The number I usually see though is 1.15 MBits/s (maybe you need the rest for the system data stream). You can then calculate the video compression ratio from the numbers here to be about 26:1. If you step back and think about that, it's little short of a miracle. Of course, it's lossy compression, but it can be pretty hard sometimes to see the loss, if you're comparing the SIF original to the SIF decompressed. There is, however, a very noticeable loss if you're coming from CCIR-601 and have to decimate to SIF, but that's another matter. I'm not counting that in the 26:1. The standard also provides for other bit rates ranging from 32Kbits/s for a single channel, up to 448 Kbits/s for stereo. Q. What's phase II? A. As I said, there is a considerable loss of quality in going from CCIR-601 to SIF resolution. For entertainment video, it's simply not acceptable. You want to use more bits and code all or almost all the CCIR-601 data. From subjective testing at the Japan meeting in November 1991, it seems that 4 MBits/s can give very good quality compared to the original CCIR-601 material. The objective of phase II is to define a bit stream optimized for these resolutions and bit rates. Q. Why not just scale up what you're doing with MPEG I? A. The main difficulty is the interlacing. The simplest way to extend MPEG I to interlaced material is to put the fields together into frames (720x486x30/s). This results in bad motion artifacts that stem from the fact that moving objects are in different places in the two fields, and so don't line up in the frames. Compressing and decompressing without taking that into account somehow tends to muddle the objects in the two different fields. The other thing you might try is to code the even and odd field streams separately. This avoids the motion artifacts, but as you might imagine, doesn't get very good compression since you are not using the redundancy between the even and odd fields where there is not much motion (which is typically most of image). Or you can code it as a single stream of fields. Or you can interpolate lines. Or, etc. etc. There are many things you can try, and the point of MPEG II is to figure out what works well. MPEG II is not limited to consider only derivations of MPEG I. There were several non-MPEG I-like schemes in the competition in November, and some aspects of those algorithms may or may not make it into the final standard for entertainment video compression. Q. So what works? A. Basically, derivations of MPEG I worked quite well, with one that used wavelet subband coding instead of DCT's that also worked very well. Also among the worked-very-well's was a scheme that did not use B frames at all, just I and P's. All of them, except maybe one, did some sort of adaptive frame/field coding, where a decision is made on a macroblock basis as to whether to code that one as one frame macroblock or as two field macroblocks. Some other aspects are how to code I-frames--some suggest predicting the even field from the odd field. Or you can predict evens from evens and odds or odds from evens and odds or any field from any other field, etc. Q. So what works? A. Ok, we're not really sure what works best yet. The next step is to define a "test model" to start from, that incorporates most of the salient features of the worked-very-well proposals in a simple way. Then experiments will be done on that test model, making a mod at a time, and seeing what makes it better and what makes it worse. Example experiments are, B's or no B's, DCT vs. wavelets, various field prediction modes, etc. The requirements, such as implementation cost, quality, random access, etc. will all feed into this process as well. Q. When will all this be finished? A. I don't know. I'd have to hope in about a year or less. Q. How do I join MPEG? A. You don't join MPEG. You have to participate in ISO as part of a national delegation. How you get to be part of the national delegation is up to each nation. I only know the U.S., where you have to attend the corresponding ANSI meetings to be able to attend the ISO meetings. Your company or institution has to be willing to sink some bucks into travel since, naturally, these meetings are held all over the world. (For example, Paris, Santa Clara, Kurihama Japan, Singapore, Haifa Israel, Rio de Janeiro, London, etc.) Q. Well, then how do I get the documents, like the MPEG I draft? A. MPEG is a draft ISO standard. It's exact name is ISO CD 11172. The draft consists of three parts: System, Video, and Audio. The System part (11172-1) deals with synchronization and multiplexing of audio-visual information, while the Video (11172-2) and Audio part (11172-3) address the video and the audio compression techniques respectively. You may order it from your national standards body (e.g. ANSI in the USA) or buy it from companies like OMNICOM phone +44 438 742424 FAX +44 438 740154 ------------------------------------------------------------------------------ Subject: [72] What is wavelet theory? Preprints and software are available by anonymous ftp from the Yale Mathematics Department computer ceres.math.yale.edu[130.132.23.22], in pub/wavelets and pub/software. epic and hcompress are wavelet coders. (For source code, see item 15 in part one). Bill Press of Harvard/CfA has made some things available for anonymous ftp on cfata4.harvard.edu [128.103.40.79] in directory /pub. There is a short TeX article on wavelet theory (wavelet.tex, to be included in a future edition of Numerical Recipes), some sample wavelet code (wavelet.f, in FORTRAN - sigh), and a beta version of an astronomical image compression program which he is currently developing (FITS format data files only, in fitspress08.tar.Z). A mailing list dedicated to research on wavelets has been set up at the University of South Carolina. To subscribe to this mailing list, send a message with "subscribe" as the subject to wavelet@math.scarolina.edu. A 5 minute course in wavelet transforms, by Richard Kirk : Do you know what a Haar transform is? Its a transform to another orthonormal space (like the DFT), but the basis functions are a set of square wave bursts like this... +--+ +------+ + | +------------------ + | +-------------- +--+ +------+ +--+ +------+ ------+ | +------------ --------------+ | + +--+ +------+ +--+ +-------------+ ------------+ | +------ + | + +--+ +-------------+ +--+ +---------------------------+ ------------------+ | + + + +--+ This is the set of functions for an 8-element 1-D Haar transform. You can probably see how to extend this to higher orders and higher dimensions yourself. This is dead easy to calculate, but it is not what is usually understood by a wavelet transform. If you look at the eight Haar functions you see we have four functions that code the highest resolution detail, two functions that code the coarser detail, one function that codes the coarser detail still, and the top function that codes the average value for the whole `image'. Haar function can be used to code images instead of the DFT. With bilevel images (such as text) the result can look better, and it is quicker to code. Flattish regions, textures, and soft edges in scanned images get a nasty `blocking' feel to them. This is obvious on hardcopy, but can be disguised on color CRTs by the effects of the shadow mask. The DCT gives more consistent results. This connects up with another bit of maths sometimes called Multispectral Image Analysis, sometimes called Image Pyramids. Suppose you want to produce a discretely sampled image from a continuous function. You would do this by effectively `scanning' the function using a sinc function [ sin(x)/x ] `aperture'. This was proved by Shannon in the `forties. You can do the same thing starting with a high resolution discretely sampled image. You can then get a whole set of images showing the edges at different resolutions by differencing the image at one resolution with another version at another resolution. If you have made this set of images properly they ought to all add together to give the original image. This is an expansion of data. Suppose you started off with a 1K*1K image. You now may have a 64*64 low resolution image plus difference images at 128*128 256*256, 512*512 and 1K*1K. Where has this extra data come from? If you look at the difference images you will see there is obviously some redundancy as most of the values are near zero. From the way we constructed the levels we know that locally the average must approach zero in all levels but the top. We could then construct a set of functions out of the sync functions at any level so that their total value at all higher levels is zero. This gives us an orthonormal set of basis functions for a transform. The transform resembles the Haar transform a bit, but has symmetric wave pulses that decay away continuously in either direction rather than square waves that cut off sharply. This transform is the wavelet transform ( got to the point at last!! ). These wavelet functions have been likened to the edge detecting functions believed to be present in the human retina. Loren I. Petrich adds that order 2 or 3 Daubechies discrete wavelet transforms have a speed comparable to DCT's, and usually achieve compression a factor of 2 better for the same image quality than the JPEG 8*8 DCT. (See item 25 in part 1 of this FAQ for references on fast DCT algorithms.) ------------------------------------------------------------------------------ Subject: [73] What is the theoretical compression limit? There is no compressor that is guaranteed to compress all possible input files. If it compresses some files, then it must enlarge some others. This can be proven by a simple counting argument (see question 9). As an extreme example, the following algorithm achieves 100% compression for one special input file and enlarges all other files by only one bit: - if the input data is , output an empty file. - otherwise output one bit (zero or one) followed by the input data. The concept of theoretical compression limit is meaningful only if you have a model for your input data. See question 70 above for some examples of data models. ------------------------------------------------------------------------------ Subject: [74] Introduction to JBIG A short introduction, written by Mark Adler : JBIG losslessly compresses binary (one-bit/pixel) images. (The B stands for bi-level.) Basically it models the redundancy in the image as the correlations of the pixel currently being coded with a set of nearby pixels called the template. An example template might be the two pixels preceding this one on the same line, and the five pixels centered above this pixel on the previous line. Note that this choice only involves pixels that have already been seen from a scanner. The current pixel is then arithmetically coded based on the eight-bit (including the pixel being coded) state so formed. So there are (in this case) 256 contexts to be coded. The arithmetic coder and probability estimator for the contexts are actually IBM's (patented) Q-coder. The Q-coder uses low precision, rapidly adaptable (those two are related) probability estimation combined with a multiply-less arithmetic coder. The probability estimation is intimately tied to the interval calculations necessary for the arithmetic coding. JBIG actually goes beyond this and has adaptive templates, and probably some other bells and whistles I don't know about. You can find a description of the Q-coder as well as the ancestor of JBIG in the Nov 88 issue of the IBM Journal of Research and Development. This is a very complete and well written set of five articles that describe the Q-coder and a bi-level image coder that uses the Q-coder. You can use JBIG on grey-scale or even color images by simply applying the algorithm one bit-plane at a time. You would want to recode the grey or color levels first though, so that adjacent levels differ in only one bit (called Gray-coding). I hear that this works well up to about six bits per pixel, beyond which JPEG's lossless mode works better. You need to use the Q-coder with JPEG also to get this performance. Actually no lossless mode works well beyond six bits per pixel, since those low bits tend to be noise, which doesn't compress at all. Anyway, the intent of JBIG is to replace the current, less effective group 3 and 4 fax algorithms. Another introduction to JBIG, written by Hank van Bekkem : The following description of the JBIG algorithm is derived from experiences with a software implementation I wrote following the specifications in the revision 4.1 draft of September 16, 1991. The source will not be made available in the public domain, as parts of JBIG are patented. JBIG (Joint Bi-level Image Experts Group) is an experts group of ISO, IEC and CCITT (JTC1/SC2/WG9 and SGVIII). Its job is to define a compression standard for lossless image coding ([1]). The main characteristics of the proposed algorithm are: - Compatible progressive/sequential coding. This means that a progressively coded image can be decoded sequentially, and the other way around. - JBIG will be a lossless image compression standard: all bits in your images before and after compression and decompression will be exactly the same. In the rest of this text I will first describe the JBIG algorithm in a short abstract of the draft. I will conclude by saying something about the value of JBIG. JBIG algorithm. -------------- JBIG parameter P specifies the number of bits per pixel in the image. Its allowable range is 1 through 255, but starting at P=8 or so, compression will be more efficient using other algorithms. On the other hand, medical images such as chest X-rays are often stored with 12 bits per pixel, while no distorsion is allowed, so JBIG can certainly be of use in this area. To limit the number of bit changes between adjacent decimal values (e.g. 127 and 128), it is wise to use Gray coding before compressing multi-level images with JBIG. JBIG then compresses the image on a bitplane basis, so the rest of this text assumes bi-level pixels. Progressive coding is a way to send an image gradually to a receiver instead of all at once. During sending, more detail is sent, and the receiver can build the image from low to high detail. JBIG uses discrete steps of detail by successively doubling the resolution. The sender computes a number of resolution layers D, and transmits these starting at the lowest resolution Dl. Resolution reduction uses pixels in the high resolution layer and some already computed low resolution pixels as an index into a lookup table. The contents of this table can be specified by the user. Compatibility between progressive and sequential coding is achieved by dividing an image into stripes. Each stripe is a horizontal bar with a user definable height. Each stripe is separately coded and transmitted, and the user can define in which order stripes, resolutions and bitplanes (if P>1) are intermixed in the coded data. A progressive coded image can be decoded sequentially by decoding each stripe, beginning by the one at the top of the image, to its full resolution, and then proceeding to the next stripe. Progressive decoding can be done by decoding only a specific resolution layer from all stripes. After dividing an image into bitplanes, resolution layers and stripes, eventually a number of small bi-level bitmaps are left to compress. Compression is done using a Q-coder. Reference [2] contains a full description, I will only outline the basic principles here. The Q-coder codes bi-level pixels as symbols using the probability of occurrence of these symbols in a certain context. JBIG defines two kinds of context, one for the lowest resolution layer (the base layer), and one for all other layers (differential layers). Differential layer contexts contain pixels in the layer to be coded, and in the corresponding lower resolution layer. For each combination of pixel values in a context, the probability distribution of black and white pixels can be different. In an all white context, the probability of coding a white pixel will be much greater than that of coding a black pixel. The Q-coder assigns, just like a Huffman coder, more bits to less probable symbols, and so achieves compression. The Q-coder can, unlike a Huffmann coder, assign one output codebit to more than one input symbol, and thus is able to compress bi-level pixels without explicit clustering, as would be necessary using a Huffman coder. Maximum compression will be achieved when all probabilities (one set for each combination of pixel values in the context) follow the probabilities of the pixels. The Q-coder therefore continuously adapts these probabilities to the symbols it sees. JBIG value. ---------- In my opinion, JBIG can be regarded as two combined devices: - Providing the user the service of sending or storing multiple representations of images at different resolutions without any extra cost in storage. Differential layer contexts contain pixels in two resolution layers, and so enable the Q-coder to effectively code the difference in information between the two layers, instead of the information contained in every layer. This means that, within a margin of approximately 5%, the number of resolution layers doesn't effect the compression ratio. - Providing the user a very efficient compression algorithm, mainly for use with bi-level images. Compared to CCITT Group 4, JBIG is approximately 10% to 50% better on text and line art, and even better on halftones. JBIG is however, just like Group 4, somewhat sensitive to noise in images. This means that the compression ratio decreases when the amount of noise in your images increases. An example of an application would be browsing through an image database, e.g. an EDMS (engineering document management system). Large A0 size drawings at 300 dpi or so would be stored using five resolution layers. The lowest resolution layer would fit on a computer screen. Base layer compressed data would be stored at the beginning of the compressed file, thus making browsing through large numbers of compressed drawings possible by reading and decompressing just the first small part of all files. When the user stops browsing, the system could automatically start decompressing all remaining detail for printing at high resolution. [1] "Progressive Bi-level Image Compression, Revision 4.1", ISO/IEC JTC1/SC2/WG9, CD 11544, September 16, 1991 [2] "An overview of the basic principles of the Q-coder adaptive binary arithmetic coder", W.B. Pennebaker, J.L. Mitchell, G.G. Langdon, R.B. Arps, IBM Journal of research and development, Vol.32, No.6, November 1988, pp. 771-726 (See also the other articles about the Q-coder in this issue) ------------------------------------------------------------------------------ Subject: [75] Introduction to JPEG Here is a brief overview of the inner workings of JPEG, plus some references for more detailed information, written by Tom Lane . Please read item 19 in part 1 first. JPEG works on either full-color or gray-scale images; it does not handle bilevel (black and white) images, at least not efficiently. It doesn't handle colormapped images either; you have to pre-expand those into an unmapped full-color representation. JPEG works best on "continuous tone" images; images with many sudden jumps in color values will not compress well. There are a lot of parameters to the JPEG compression process. By adjusting the parameters, you can trade off compressed image size against reconstructed image quality over a *very* wide range. You can get image quality ranging from op-art (at 100x smaller than the original 24-bit image) to quite indistinguishable from the source (at about 3x smaller). Usually the threshold of visible difference from the source image is somewhere around 10x to 20x smaller than the original, ie, 1 to 2 bits per pixel for color images. Grayscale requires a little bit less space. JPEG defines a "baseline" lossy algorithm, plus optional extensions for progressive and hierarchical coding. There is also a separate lossless compression mode; this typically gives about 2:1 compression, ie about 12 bits per color pixel. Most currently available JPEG hardware and software handles only the baseline mode. Here's the outline of the baseline compression algorithm: 1. Transform the image into a suitable color space. This is a no-op for grayscale, but for color images you generally want to transform RGB into a luminance/chrominance color space (YCbCr, YUV, etc). The luminance component is grayscale and the other two axes are color information. The reason for doing this is that you can afford to lose a lot more information in the chrominance components than you can in the luminance component; the human eye is not as sensitive to high-frequency color info as it is to high-frequency luminance. (See any TV system for precedents.) You don't have to change the color space if you don't want to, as the remainder of the algorithm works on each color component independently, and doesn't care just what the data is. However, compression will be less since you will have to code all the components at luminance quality. 2. (Optional) Downsample each component by averaging together groups of pixels. The luminance component is left at full resolution, while the color components are usually reduced 2:1 horizontally and either 2:1 or 1:1 (no change) vertically. In JPEG-speak these alternatives are usually called 2h2v and 2h1v sampling, but you may also see the terms "411" and "422" sampling. This step immediately reduces the data volume by one-half or one-third, while having almost no impact on perceived quality. (Obviously this would not be true if you tried it in RGB color space...) Note that downsampling is not applicable to gray-scale data. 3. Group the pixel values for each component into 8x8 blocks. Transform each 8x8 block through a discrete cosine transform (DCT); this is a relative of the Fourier transform and likewise gives a frequency map, with 8x8 components. Thus you now have numbers representing the average value in each block and successively higher-frequency changes within the block. The motivation for doing this is that you can now throw away high-frequency information without affecting low-frequency information. (The DCT transform itself is reversible except for roundoff error.) See question 25 for fast DCT algorithms. 4. In each block, divide each of the 64 frequency components by a separate "quantization coefficient", and round the results to integers. This is the fundamental information-losing step. A Q.C. of 1 loses no information; larger Q.C.s lose successively more info. The higher frequencies are normally reduced much more than the lower. (All 64 Q.C.s are parameters to the compression process; tuning them for best results is a black art. It seems likely that the best values are yet to be discovered. Most existing coders use simple multiples of the example tables given in the JPEG standard.) 5. Encode the reduced coefficients using either Huffman or arithmetic coding. (Strictly speaking, baseline JPEG only allows Huffman coding; arithmetic coding is an optional extension.) Notice that this step is lossless, so it doesn't affect image quality. The arithmetic coding option uses Q-coding; it is identical to the coder used in JBIG (see question 74). Be aware that Q-coding is patented. Most existing implementations support only the Huffman mode, so as to avoid license fees. The arithmetic mode offers maybe 5 or 10% better compression, which isn't enough to justify paying fees. 6. Tack on appropriate headers, etc, and output the result. In an "interchange" JPEG file, all of the compression parameters are included in the headers so that the decompressor can reverse the process. For specialized applications, the spec permits the parameters to be omitted from the file; this saves several hundred bytes of overhead, but it means that the decompressor must know what parameters the compressor used. The decompression algorithm reverses this process, and typically adds some smoothing steps to reduce pixel-to-pixel discontinuities. Extensions: The progressive mode is intended to support real-time transmission of images. It allows the DCT coefficients to be sent incrementally in multiple "scans" of the image. With each scan, the decoder can produce a higher-quality rendition of the image. Thus a low-quality preview can be sent very quickly, then refined as time allows. Notice that the decoder must do essentially a full JPEG decode cycle for each scan, so this scheme is useful only with fast decoders (meaning dedicated hardware, at least at present). However, the total number of bits sent can actually be somewhat less than is necessary in the baseline mode, especially if arithmetic coding is used. So progressive coding might be useful even if the decoder will simply save up the bits and make only one output pass. The hierarchical mode represents an image at multiple resolutions. For example, one could provide 512x512, 1024x1024, and 2048x2048 versions of the image. The higher-resolution images are coded as differences from the next smaller image, and thus require many fewer bits than they would if stored independently. (However, the total number of bits will be greater than that needed to store just the highest-resolution frame.) Note that the individual frames in a hierarchical sequence may be coded progressively if desired. Lossless JPEG: The separate lossless mode does not use DCT, since roundoff errors prevent a DCT calculation from being lossless. For the same reason, one would not normally use colorspace conversion or downsampling, although these are permitted by the standard. The lossless mode simply codes the difference between each pixel and the "predicted" value for the pixel. The predicted value is a simple function of the already-transmitted pixels just above and to the left of the current one (eg, their average; 8 different predictor functions are permitted). The sequence of differences is encoded using the same back end (Huffman or arithmetic) used in the lossy mode. The main reason for providing a lossless option is that it makes a good adjunct to the hierarchical mode: the final scan in a hierarchical sequence can be a lossless coding of the remaining differences, to achieve overall losslessness. This isn't quite as useful as it may at first appear, because exact losslessness is not guaranteed unless the encoder and decoder have identical IDCT implementations (ie identical roundoff errors). References: For a good technical introduction to JPEG, see: Wallace, Gregory K. "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. (Adjacent articles in that issue discuss MPEG motion picture compression, applications of JPEG, and related topics.) If you don't have the CACM issue handy, a PostScript file containing a revised version of this article is available at ftp.uu.net, graphics/jpeg/wallace.ps.Z. The file (actually a preprint for an article to appear in IEEE Trans. Consum. Elect.) omits the sample images that appeared in CACM, but it includes corrections and some added material. Note: the Wallace article is copyright ACM and IEEE, and it may not be used for commercial purposes. An alternative, more leisurely explanation of JPEG can be found in "The Data Compression Book" by Mark Nelson ([Nel 1991], see question 7). This book provides excellent introductions to many data compression methods including JPEG, plus sample source code in C. The JPEG-related source code is far from industrial-strength, but it's a pretty good learning tool. An excellent textbook about JPEG is "JPEG Still Image Data Compression Standard" by William B. Pennebaker and Joan L. Mitchell. Published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 650 pages, price US$59.95. (VNR will accept credit card orders at 800/842-3636, or get your local bookstore to order it.) This book includes the complete text of the ISO JPEG standards, DIS 10918-1 and draft DIS 10918-2. Review by Tom Lane: "This is by far the most complete exposition of JPEG in existence. It's written by two people who know what they are talking about: both serve on the ISO JPEG standards committee. If you want to know how JPEG works or why it works that way, this is the book to have." The official specification of JPEG is not currently available on-line. I hear that CCITT specs may be on-line sometime soon, which would change this. At the moment, your best bet is to buy the Pennebaker and Mitchell textbook. Archive-name: compression-faq/part3 Last-modified: May 19th, 1993 This file is part 3 of a set of Frequently Asked Questions for the groups comp.compression and comp.compression.research. If you did not get part 1 or 2, you can get them by ftp on rtfm.mit.edu in directory /pub/usenet/news.answers/compression-faq If you don't want to see this FAQ regularly, please add the subject line to your kill file. If you have corrections or suggestions for this FAQ, send them to Jean-loup Gailly . Thank you. Contents ======== Part 3: (Long) list of image compression hardware [85] Image compression hardware [99] Acknowledgments Search for "Subject: [#]" to get to question number # quickly. Some news readers can also take advantage of the message digest format used here. ------------------------------------------------------------------------------ Subject: [85] Image compression hardware Here is a list of sources of image compression hardware (JPEG, MPEG, H.261 and others), reposted with the author's permission. The list is probably a little dated already, but it is a good starting point for seeking compression chips. (Please send corrections/additions to jloup@chorus.fr). References are taken from: VIDEO COMPRESSION OPTIONS, IEEE CICC 6-May-92 John J. Bloomer, jbloomer@crd.ge.com, Fathy F. Yassa, Aiman A. Abdel-Malek General Electric Corporate R&D, KWC317 Signals and Systems Laboratory PO Box 8, Schenectady NY, 12301 Some comments are from C. Fogg and George Warner . Pipelined Processors, Building Blocks (Chip Sets) ------------------------------------------------- STI3200, IMSA121, STI3208 - SGS-Thompson DCT processors. 602-867-6279 - 3200 has multiple block size options, DC to 13.5 MHz - A121 8x8 fixed blocks, DC to 20MHz, add/sub loop, CCITT compatible - 3208 8x8 fixed blocks, DC to 40MHz, CCITT compatible at 20MHz STI3220 - SGS-Thompson motion estimator (H.261, MPEG). 602-867-6279 - 8-bit input pixels, 4-bit H and V vectors out - adjustable block size matcher (8x8, 8x16, 16x16) - +7/-8 search window - 5V, 2W at 18MHz (max), 68 pin PLCC L64765 , L64735 , L64745 - 3-chip LSI Logic JPEG set. 408-433-4383 - L64765 raster-to-block and color-space converter, jointly developed with Rapid Tech. - L64735 block DCT processor - L64745 JPEG coder support, stand-alone lossless DPCM codec, dynamic Huffman - 27 MB/s on CCIR601 frames - minimal support logic, color and gray scale - 68-pin PGA or PLCC, 27 and 20 MHz versions L647*0 and L6471* families - LSI Logic H.621/MPEG pieces. 408-433-8000 - L64720 motion estimator, 30/40MHz, 8x8, 16x16 blocks, 32x32 or 16x16 search window, 68-pin CPGA or PPGA - L64730 & 735 8x8 DCT processors (12 & 8-9 bits) - L64740 8x8 block quantization - L64760 intra/inter-frame coding decision - L64715 BCH error correction - L64750/L64751 variable length encode/decode (H.261-specific) ZR36020 and ZR36031 - Zoran DCT processor & quantization/encoding. 408-986-1314 - JPEG-like scheme using 16-bit, two's complement fixed point arithmetic - includes bit-rate controls for constant # of pictures per card - 7.4 MHz, < 1W, 20mW in standby mode, 7.5 frames/s (f/s) - 36020 - 44-pin plastic quad flatpack (PQFP) or 48-pin ceramic DIP - 36031 - 100-pin PQFP or 85-pin PGA. - co-developments with Fuji Photo Film Co. Ltd. digital IC-card camera market Does 2-passes of image: generate histogram for optimum Huffman tables and quantization compute step size (ala H.261 and MPEG-I) for each macroblock or minimum coded unit (MCU). JPEG-compatible codec expected soon. LDM3104 - Olympus DCT coefficient encoder - constant rate, digital IC-card camera market - 750 mW, 25 mW standby, 100-poin QFP TMC2312 - TRW quantizer/Huffman encoder, TMC2313 Huffman decoder/dequantizer TMC2311 - TRW CMOS Fast Cosine Transform Processor. - 12 Bits, 15 M pixels/s - complies with the CCITT SGXV ( e.g. JPEG, H.261 and MPEG ) - includes an adder-subtractor for linear predictive coding MN195901 - Matsushita Electric Industrial Co. See ISSCC 1992 - 16-bit, 60 MIP video signal processor - 25 uS instruction processing - on-board DCT and absolute differencing - Philips Signetics US fab. HGCT - Ricoh CRC, Generalized Chen Transform demonstration chip. 408-281-1436 - 2D JPEG/MPEG/H.261 compatible DCT - includes quantization - 30MHz, 15K gates - licensing possible GCTX64000 - Graphic Communication Technology Corp. chipset - provides CCITT H.261 - VLSI Technology and Hitachi supply H.261 codec core. 1 micron CMOS. BT - British Telecommunications plc., Martlesham labs designed - H.261 codec chipset, Motorola fab. - 13 chips total for codec. Pipelined Processors, Monolithic, Programmable ---------------------------------------------- Vision Processor - Integrated Information Technology Inc. 408-727-1885 - generic DCT, motion compensated & entropy coding codec - microcode for still- and motion-video compression (JPEG, H.261 and MPEG1) - 1 micron CMOS, 20 MHz and 33 MHz, PGA and 84-pin QFP - JPEG only and JPEG/H/261/MPEG versions available, H.261 at 30 f/s. - used by Compression Labs, Inc. CDV teleconferencing system - rumored to be the heart of the AT&T picture phone MN195901 - Matsushita Electric Industrial Corp - 40 MHz DSP, built-in DCT - 16-bit fixed-point AVP1000 - Motorola JPEG, MPEG and H.261 codec chipset. 800-372-2447 - 1400D decoder, 1400C system controller - 1300E H.261 (CIF, QCIF, CIF240) at 30 f/s, I-frame only MPEG. - 1400E is superset of 1300E, motion with 1/2 pixel resolution over +/- 32 pixels - YCbCr video or digital input, on-board rate FIFOs, external RAM required - 0.75 micron, 50 MHz CMOS AVP1000 is from AT&T Microelectronics. The AT&T chip set handles MPEG-1, H.261, and JPEG. 1400D has on board color space convertor. Limited to 4Mb/s coded rate. The DSP does the MUSICAM decoding (up to layer II ?) 82750PB, 82750DB - Intel DVI pixel and display YUV color space processors. - proprietary machine code employed for compression - usable for other algorithms (e.g., JPEG, H.261 or MPEG1 at reduced data rates) Pipelined Processors, Monolithic, Fixed Lossless - Entropy Coders, DPCM, VQ --------------------------------------------------------------------------- DCP - Integrated Information Tech. Inc. Data Compressor Processor 408-727-1885 - LZ codec with on-chip dictionary store - on-chip buffers supporting block moves - targeting disk drives and network controller markets - 3.3V, 84-pin PQFP Mystic - HP's DC-LZ codec. 408-749-9500 AHA3210 - Advanced Hardware Architectures DC-LZ codec. 208-883-8000 - two independent DMA ports for 10 MB/s compress, decompress & pass-thru - addressing allows up to 16 MB record compression - 20 MHz internal clock, 200 mW, 100-pin PQFP - interface to AHA5101/5121 QIC tape controller/formatter - HP licensee AHA3xxx/xxy - Rice (UNC) algorithm, 20M samples/sec, 4 to 14 bits. 208-883-8000 CRM1000 - CERAM Inc. entropy codec, proprietary algorithm. 719-540-8500 Rice - UNC algorithm prototype, 180 Mb/s. See IEEE CICC 1992 - other CICC 1992 papers: +JS.E. Kerneny et.al. differential read, pyramidal output CCD + A. Aggoun et.al. DPCM processing DCD - Philips Data Compressor Decompressor IC. 914-945-6000 - See CICC 1990 proceedings, H. Blume, et.al. - LZ codec, 20 MHz clock - Internal FIFOs, separate input/output buses, max 10 Mword/s data in - 5 V CMOS, 175-pin PGA 9705 - Second generation Stac Electronics accelerator chip. 619-431-7474 - Stacker LZA compression scheme(LZ-based) - compress at approx. 2.5 MB/s, decompress at 6 MB/s (39+ faster than 9704) - standby mode 300uA - embedded in tapes and disks (e.g., QIC-122 Ten X Technology 512-346-8360) - file compression board & software: + for the PC/AT - from Stac + for the Macintosh - from Sigma Design 415-770-0100 (40 MHz 9703) - InfoChip Systems Inc. - proprietary string-matching technology 408-727-0514 VCEP or OTI95C71/Am95C71 - Oak Technology Inc. 408-737-0888 - AMD CCITT B&W fax image compression Pipelined Processors, Monolithic, Fixed Lossy --------------------------------------------- MB86356B - Fujitsu LTD. - JPEG DIS 10918-1 baseline codec - on-chip quantizer tables - 2.5M pixel/sec input, up to 10MB/sec output - supports progressive and DPCM lossless modes - 135 pin PGA. CL550-30 - C-Cube Microsystems 408-944-6300 - JPEG-8-R2 compliant baseline codec - 350-level pipeline, on-chip Huffman and quantizer table - 44.1 MB/sec (15 MB/sec for -10) - RGB, YUV, CMYK supported, CCIR 601 in real-time - 16/32-bit host interface - 144 pin PGA or QFP, 2.5W at 29.41 MHz Limited to 2MB/sec (15Mb/s) coded rate. 35MHz PGA version available. 2:1 horizontal filter, on board programmable color space convertor. Allows on pair of quantization tables to be loaded while other pair is used to code or decode data stream. Needs maintanence by host. STI140 - SGS-Thompson JPEG baseline codec. 617-259-0300 [** Now cancelled **] - see CICC 1991 proceedings, M. Bolton. - 20 Mpixel/sec input, up to 20 MB/sec output - supports 24-bit color, 8-bit grey and 12-bit extended pixels - on chip Huffman and quantizer tables - 144 pin PQFP, 5V, < 2W., 10mW power-down mode - 1.2 micron, 3-layer metal CMOS, 20 MHz. ` UVC7710 - UVC Corp. Integrated Multimedia Processor. 714-261-5336 - proprietary, patented intra-frame compression, on-chip code tables - 20-35:1, 12.5 Mpixels/sec., compressed audio - includes much of the PC-AT (16-bit ISA) bus interface logic - 128 pin PJQFP plastic CL950 - C-Cube/JVC implementation of the MPEG-JVC or extended mode MPEG2 announced. 6-9 Mb/sec. JVC mode is not MPEG-II compliant (there isn't an MPEG2 standard yet) but is an extension of MPEG1 at a higher rate plus interlace video handling. CL450 - Announced June 1992. Scaled down version of CL950, with 3Mb/sec limit. Does not code or decode JPEG, only MPEG-I decoding. CD-I - ASICs planned for CD-ROM, Compact Disk-Interactive defacto standards - CD-ROM XA - Sony-Philips-Motorola-Microsoft - CDTV - Commodore. YUV processing. - audio ADPCM encode/decode PC/AT boards available from Sony 408-432-0190 Phillips has exclusively contracted the CL450 for use in motion video expansion slot on CD-I players. Codecs Chips Under Development ------------------------------ MPEG1 codec chips due from - TI, Brooktree, Cypress Semiconductor, Motorola (successor to the DSP96002 Multimedia Engine), Xing Technology/Analog Devices, Sony and C-Cube Windbond Electronics Corp. is developing a DSP chip for CD-I, MPEG and JPEG Using these Chips: Board Level Compression Hardware ------------------------------------------------------ + JPEG Using CL550 + JPEG Using Other Chip Sets + DSP Chip Based JPEG/MPEG Solutions + Integrated Compressed Digital Video Boards JPEG Using CL550 --------------- C-Cube - 408-944-6300 ISA and NuBus boards - for development and limited time-constraint applications - 1-2.5 MB/sec host bus constraints - Image Compression Interface (ISI) software for 3rd party CL550 integration VideoSpigot/SuperSqueeze - SuperMac Technology 408-245-2202 - a CL550A on a NuBus board - 24 frame/s with CD-quality audio - reads from Winchester and magneto-optic drives Fluency VSA-1000 - Fluent Machines, Inc. AT board set. 508 626-2144 - compress/decompress real-time synced audio & video to a i386 PC Winchester - NTSC or PAL input, 320x240 pixels saved - uses i960 chip, no additional boards needed - M/S Windows support, 3rd party S/W (e.g., AimTech 603-883-0220) Super Motion Compression - New Media Graphics PC/AT board. 800 288-2207 - 8Khz, 8-bit compressed audio - 30 f/s JPEG to & from disk - earlier reports: still-frame compression in several seconds per MB Leadview - Lead Tech Inc. AT board uses the CL550 to compress/decompress JFIF or JTIF format files Monalisa - Opta Inc. AT board uses the CL550 Squeeze - Rapid Technology AT board - Integrated by a number of vendors into 3rd party multimedia, video-editing PC stations Parallax Graphics - SBus, VME and PC-AT boards. 408-727-2220 Chips and Technologies - JPEG development kit due. JPEG Using Other Chipsets ------------------------- Visionary - Rapid Technology JPEG AT board. 716-833-8534 - LSI Logic JPEG chips L647-35, -45 & -65 - 30 f/s motion JPEG - 256x240 pixel compression and display from CCIR-601 input - private codec-frame buffer bus - also integrated with TrueVision multimedia hardware Media 100 - Data Translation nonlinear video production system for the Macintosh (QuickTime). 22 MB/s (PAL) and 18MB/s (NTSC) throughput. Alice - Telephoto Communications Inc. 619-452-0903 - Alice-H350 (PC/AT) and -H365 (PS/2) codec boards - use a 40 MHz TMS320C51 DSP and a IMSA121 DCT processor chip - JPEG (lossy and lossless), CCITT G3/G4, color and grey-scale images Xing Technology - Hardware accelerator. 805-473-0145 - compatible with their VT-Express JPEG Turbo Accelerator Software Video/1 - PsiTech Inc. 714-968-7818 - includes a 6U VME/VSB JPEG Processing Card - compresses RS-170, NTSC, PAL or Secam video into 8 MB of on-board RAM DSP Chip Based JPEG/MPEG Solutions ---------------------------------- Optipac - Optivision Inc. PC/AT, ISA & VME codecs. 800-562-8934 - JPEG (lossless and lossy), CCITT III/IV - 1 to 5 TMS32C025s - 512x400x16-bit images in < 1 sec. XCeed ICDP-II - Micron Technology Inc. NuBus card - uses two AT&T Microelectronics DSP-16 DSP chips - driven by Storm Technologies PicturePress software - executes an enhanced JPEG algorithm at near-realtime. PicturePress Accelerator - Storm Technology 415-691-1111 (see above) - also has a line of VME compression boards - Micro Dynamics Ltd. imaging systems use Storm accelerator 301-589-6300 Picture Packer Accelerator - Video & Image Compression Corp. - AT and NuBus boards use the JPEG Open Standard and a TMS320C25 VideoPix - Software JPEG boards are offered by Sun Microsystems (S-Bus). Phoenix System - T/one Inc. uses an Optivision Optipac 3250 to talk to a Storm Technologies NuBus PicturePress Accelerator to talk JPEG over analog phone lines. Nextdimension - NeXt Computer Inc. 415-780-3912 - 24+8-bit alpha, 640x480, 30 f/s decompression - CL550 version not shipping as announced. Spirit-40 - Sonitech International Inc. ISA card. 617-235-6824 - two TMS320C40 DSPs for 80 MFLOPS - connect 16 boards in a hypercube for up to 1280 MFLOPS - JPEG, MPEG-1 audio and other voice coding applications included HardPak - CERAM Inc., ISA and EISA file compression board. 719-540-8500 - 3.4 x 1.8 inch footprint (notebook, laptops) - 32KB on-board write-thru file compression cache - CERAM also has an SBus compressive swap-space accelerator for Suns macDSP - Spectral Innovations, AT&T DSPC32-based accelerator. 408-727-1314 - JPEG functions available - 30 MFLOPS on the NuBus VCA-1 - Video compression accelerator for Sun workstations. Tel: (310)829-7733, FAX: (310)829-1694, Internet: spacecc@cerf.net Special-Purpose Hardware for Motion Estimation and DCTs Performs 8x8 DCTs in 21 microsec after first DCT at 52 microsec.* Performs 32x32 cross search for 16x16 block in 239 microsec.* (*Stated times are for a 25-MHz SBus.) Mounts in a single SBus slot. Included software allows user-transparent access. Price: $2,900 (subject to change without notice). Integrated Digital Video Boards - Miscellaneous Multimedia, Video Conferencing ------------------------------------------------------------------------------ VCI/oem - Vista Communication Instruments, Inc. +358 0 460 099 - two AT-board H.261 video codec, PAL or NTSC cameras and monitors -56 kbps (64 kbps) to 2 Mbps, 64 kbps increments - H.221 framing and synchronizing - H.241 network signalling - H.200/AV.254 forthcoming standard for compressed audio - network interface boards available MediaStation- VideoLogic Inc., JPEG compression board for ISA bus. 617-494-0530 - works with VideoLogic DVA-4000/ISA motion video board, custom bus - CL-550 plus ADPCM and PCM audio support - Inmos Transputer for I/O scheduling - Microsoft Windows Multimedia Extensions and proprietary interfaces DECspin - Digital Equipment CorpSound/Picture Information Network 508-493-5111 - full motion, true-color (24-bit) and greyscale (8-bit black & white) - variable frame size and rate up to 640 x480 x30 NTSC true-color - Internet or DECnet transmission and disk I/O of live synchronized video/audio - video teleconferencing using standard network protocols - create and edit of audio and video sequences - voice grade live audio sequences - DECmedia DECvideo and DECaudio hardware and software required ActionMedia II - Intel/IBM DVI PS/2 and PC/AT boards. 914-642-5472 - i750 processor boards for capture and delivery systems - Microsoft programming support libraries - proprietary RTV and PLV compression algorithms resident, time and time/space VQ - contact Intel Literature Center for #B4P-05 algorithm structure - Real Time Video (RTV) algorithm 1.5 , effective 128x120 pixel sequence at 30 f/s. - RTV 1.0 is 128x240 at 10 f/s. - Presentation Level Video (PLV) - extensive off-line processing, exploits inter-frame coherence. - i750 processor capable of playing-back PLV-compressed 256x240 sequences at 30 f/s. DVI Board - Fast Electronic U.S. Inc. laptop board. 508-655-3278 - uses Intel i750 chipset - compress or decompress video at up to 30 f/s EyeQ - New Video Corp. DVI boards for the Macintosh. 213-396-0282 - uses Intel i750 chipset - 150 KB/s full-motion compressed video - T1 and Winchester integration paths Copernicus 1000 & 2000 - DesignTech, 408-453-9510 - DVI-based presentation and authoring systems Spectrum Signal Processing - DSP96002-based PC-AT board - up to four boards in cascade - other TI, Analog Devices and AT&T-based DSP offerings Ariel Corp. - Dual DSP96002 PC-AT board with compression support. 201-429-2900 Capture I - UVC Corp., 16-bit ISA bus board. 714-261-5336 - 30 f/s of 640/480 interlace capture and record (uses UVC7710) - NTSC or PAL input - VPC200/201 development board set - proprietary NTSC video codec (audio card required). Leadview - Lead Technologies, Inc. accelerates an enhanced JPEG algorithm on ISA IBM - near-term availability: (1) IBM United Kingdom and British Telecommunications plc. - PC or PS/2 add-on boards by end of 1993 - interface to ISDN 2 service (one or two 64kb/s channels) - BT also planning residential videophone product with GEC Marconi Ltd. (2) IBM Japan PS/2 board - uses GCTX64000 for H.261 - ISDN (narrowband 64kb/s ) and IEEE 802.5 LAN interfaces Optibase 100 - Optibase, Inc. DSP-based compression/expansion boards. 818-719-6566 - supports JPEG - supports CCITT G.721 and ANSI T1.301 & T1.303 drafts (voice and music) - and proprietary compression (AADCT, lossless) Motorola - DSP56002 (fixed-point 40MHz version of the 56001) AT&T JPEG coder (George Warner ) - runs on a DSP3210 under the VCOS operating system. The coder can be used to simultaneously compress/decompress multiple images and/or be used in conjunction with other DSP modules to preprocess or postprocess the image data. Other modules available for the DSP3210 include audio coders (such as MPEG, SBC, CDXA, and G.722), modem/fax data pumps (V.32bis, V.22bis, and V.29), DTMF, call progress detection, sample rate conversion, and more. MWave - TI, IBM, Intermetrics multimedia system, due from IBM in 1993. Misc. NuBus boards - RasterOps , Radius, Mass Microsystems, Orange Micro, IBM M - - Motion. P.OEM - Interated Systems Inc. fractal compression boards for the PC. 404-840-0310 two desktop video conferencing products for Sparc's with the Parallax XVIDEO board: Communique! - desktop video conferencing products for Sparcs with the Parallax XVIDEO board: InSoft, Inc., 4718 Old Gettsburg Road, Executive Park West I, Suite 307 Mechanicsburg, PA 17055, USA. email: info@insoft.com phone: 717-766-6290, fax: 717-766-8866 PSVC - desktop video conferencing products for Sparcs with the Parallax XVIDEO board: Paradise Software, Inc., 55 Princeton Heightstown Rd, Suite 109 Princeton, NJ 08550, USA. email: support@paradise.com phone: 609-275-4475, fax: 609-275-4702 North Valley Research - video and other time-based media in a UNIX environment North Valley Research; 15262 NW Greenbriar Pkwy; Beaverton, OR 97006 Phone (503) 531-5707, Fax (503) 690-2320. Todd Brunhoff Boards Under Development ------------------------ Matrox - Matrox Studio line of PC boards will include a 64-bit MOVIE bus and JPEG compression. ------------------------------------------------------------------------------ Subject: [99] Acknowledgments There are too many people to cite. Thanks to all people who directly or indirectly contributed to this FAQ.