Software Vault: The Gold Collection/Software Vault - The Gold Collection (American Databankers) (1993).ISO/cdr55/cld9comp.zip/CLD9COMP.TXT

Text File | 1993-06-09 | 184KB | 4,061 lines

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 <[e-mail]>.
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 ([e-mail]). 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 <[e-mail]>)

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 <[e-mail]>

      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 <[e-mail]>
        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: [e-mail] or [e-mail]

      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: [e-mail]
         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: [e-mail]
  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 <[e-mail]>
  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:<misc.unix>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 <[e-mail]>

.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 <[e-mail]>

.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 <[e-mail]> 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 <[e-mail]>:

I called WEB at [phone] 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 <[e-mail]>:

   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 <[e-mail]>:

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 <[e-mail]> 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
<[e-mail]>, IEEE Micro, Oct 1992, pp. 41-53.

Short introduction, by Alejo Hausner <[e-mail]>:

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 [e-mail].
For more information, contact Robert Shaw <[e-mail]> or
Antoinette Bautista <[e-mail]>. Warning by John Levine
<[e-mail]>:

  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:<msdos.compress>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 precisiΦí6Xref: 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: [e-mail] (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: <[e-mail]>
Date: 9 Jun 93 13:23:27 GMT
Expires: 30 Jul 93 16:17:20 GMT
Sender: [e-mail]
Reply-To: [e-mail]
Followup-To: comp.compression
Lines: 2399
Approved: [e-mail]
Supersedes: <[e-mail]>.

------------------------------------------------------------------------------

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: [e-mail] (Independent JPEG Group)

      havefun.stanford.edu:pub/jpeg/JPEGv1.0.tar.Z
      Contact: Andy Hung <[e-mail]> (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 <[e-mail]> (see item 20 below)

      toe.cs.berkeley.edu:/pub/multimedia/mpeg/mpeg_play-2.0.tar.Z
      Contact: [e-mail]

      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 <[e-mail]>

H.261(P*64):
      havefun.stanford.edu:pub/p64/P64v1.1.tar.Z
      Contact: Andy Hung <[e-mail]> (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 <[e-mail]>
      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 <[e-mail]>

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
[phone].

------------------------------------------------------------------------------

Subject: [17] What is the state of fractal compression?


from Tal Kubo <[e-mail]>:

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 <[e-mail]> 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 <[e-mail]> 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 <[e-mail]> 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 [phone].

  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 [e-mail] 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: [phone] or 1-800-4FRACTL
fax: [phone]

------------------------------------------------------------------------------

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: [e-mail]

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 <[e-mail]> 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 <[e-mail]>.


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 <[e-mail]>.  (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 <[e-mail]>:

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 <[e-mail]>:

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
[e-mail]).  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 <[e-mail]>.
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 [e-mail] (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 <[e-mail]>:

  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 <[e-mail]>:

  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 <[e-mail]> and Carsten Bormann
<[e-mail]>:

  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 [e-mail].
  Note that the distribution is not available via E-mail (please use one
  of the ftp-via-E-mail servers).


from Bob Kimball <[e-mail]>:

  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 <[e-mail]>:

  On wsmr-simtel20.army.mil, pd1:<msdos.sound>
  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 <[e-mail]>).

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 [e-mail]
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 [e-mail]

------------------------------------------------------------------------------

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 [e-mail].

Rodney Peck <[e-mail]> 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
[e-mail].


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 <[e-mail]>:

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 <[e-mail]>.  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 <[e-mail]>.

 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.

<The LZ78 family of compressors>

  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
    <END>               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]


<The LZ77 family of compressors>

  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
<[e-mail]> also posts a FAQ specialized in MPEG.

Introduction written by Mark Adler <[e-mail]> 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 [phone]
     FAX [phone]

------------------------------------------------------------------------------

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 [e-mail].


A 5 minute course in wavelet transforms, by Richard Kirk <[e-mail]>:

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 <[e-mail]> 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 <insert your favorite one here>, 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 <[e-mail]>:

  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 <[e-mail]>:

  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
<[e-mail]>.  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 <[e-mail]>.  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
[e-mail]). References are taken from:

   VIDEO COMPRESSION OPTIONS, IEEE CICC 6-May-92
   John J. Bloomer, [e-mail], 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 <[e-mail]> and George Warner
<[e-mail]>.


 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: [phone], FAX: [phone], Internet: [e-mail]
         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. [phone]
 - 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 <[e-mail]>)
        - 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: [e-mail]
        phone: [phone], fax: [phone]

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: [e-mail]
 phone: [phone], fax: [phone]

North Valley Research - video and other time-based media in a UNIX environment
        North Valley Research; 15262 NW Greenbriar Pkwy; Beaverton, OR  97006
        Phone [phone], Fax [phone]. Todd Brunhoff <[e-mail]>

 Boards Under Development
 ------------------------

Matrox - Matrox Studio line of PC boards will include a 64-bit MOVIE bus and
         JPEG compression.


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Subject: [99] Acknowledgments


There are too many people to cite. Thanks to all people who directly
or indirectly contributed to this FAQ.