From: parker@shape.mps.ohio-state.edu (Steve Parker)
Newsgroups: comp.lang.perl,comp.compression,comp.lang.postscript
Subject: postscript compression script in perl.
Date: 3 Sep 1992 12:52:31 -0400
Organization: Department of Mathematics, The Ohio State University
Distribution: world
NNTP-Posting-Host: shape.mps.ohio-state.edu
Keywords: compression compress postscript perl

To Whom It May Concern,

A few months ago I posted a request to the net regarding a postscript
compression routine.  I have since found out that Postscript 2 is to have
it's own standard way to compress images, nevertheless I have written a
postscript image compressor.

The postscript compressor I have written is in perl but the form of compression
is run-length encoding, and could be written in other languages, such as C, sed,
awk, nawk, etc. (I am sure that Larry could probably even write the thing in
roff--the man is mutant! ceveat: I am forever in his debt for writting perl.)

The most common responce that I received when telling my peers of my plans was
"Why write the thing in postscript?" or "Why write the thing at all?"

Everyone knows that the way screen dump/image capture routines output their
results on various architures is straight forward but disk wasteful.  Computer
screen images are not like images from other sources in that they almost always
have huge amounts of repetition, large areas all the same pattern.  And are
therefore very susceptible to run-length-encoding-type compression schemes.

The reasons I think that a compression routine written in postscript is valuable
are that the resulting compressed image is still a valid posctscript program,
which can be sent via E-mail without fear of corruption to anyone with a
postscript printer regardless of the machine to which it is connected, and
futhermore can be subsequently compressed with your favorite routine:
compress, pack, zip, zoo, arc, etc.

Finally I realize that this is not the most efficient method, but before I work
on enhancing it, I thought that I'd post it.  I would like your input on how to
improve it and I thought that many of you could use it 'as is' to help with
disk space problems (a never-ending problem at our site at least).  I have found
that users mind this form of compression less since it requires no additional
actions to print the file later.

If you use this package, I would appreciate timing results/comments/suggestions.
Please E-mail me any posts that you might make concerning this post so that
I will post a summary at a later date:

 Steve Parker                    parker@mps.ohio-state.edu
 Dept of Chemistry               201 McPherson Labs
 Ohio State University           614-292-5042

I have thought of many ways to improve this script:

1) Record which and how many of the decompression routines were used in a given
   image, and insert only those that were used and in the order of fequency
   that they were used.
2) Search the unique runs for patterns of 2 4 or 8 characters.
3) Make a new decompression routine called I for insert which would be used for
   inserting unique string into a long run of repeating characters.

NOTE: The above ideas would most easily be accomplished by saving the compressed
      image in memory or a temp file and/or making multiple passes at the image
      data.

Any other suggestions?

Here are timing results for postscript images created on various machines,
compressed on a Sparc ELC and printed on a AppleLaserWriter II:


Test cases:

					   		 (Apple LaserWriter II)
Filename	size in	chars	  bits in	time to     approximate time
                	     	   image	compress	 to print
-------------------------------------------------------------------------
snapshot.cmp.ps    63861	     ---	 67.0 s  	  100 s
snapshot.ps	  262906	   1024000	    --		  245 s
stripes.cmp.ps	    2241	     ---	 31.0 s		   30 s
stripes.ps	  133403	   1036800	    --  	  130 s
iris.cmp.ps	   73384   	     ---	 68.5 s		  100 s
iris.ps		  261385	    524288	    --  	  250 s
stellar.cmp.ps	  129140	     ---	 1027.3 s 	  425 s
stellar.ps	 1968436	   1966728	    --  	 1740 s

I am presently getting results for NeXT printers, and some others.

These files are available by E-mail at request to above address.

Here is my description of the two pieces necessary for
compression/decompression (I originally had two files but now use the <DATA>
file handle of perl):

decomp.header	is the postscript decompression header that will be used in
		place of
		"/picstr 1024 string def
		 { currentfile /picstr readhexstring pop }"
		which is often used as the proc for the image function
		ie "width hieght bitpersample proc image"

pscmp		is the perl script that compresses the hex digit pair
		format often used to encode a bitmap in postscript, it also
		inserts the decompression header file in a clever way.
		Since the last thing on the stack before the image command
		is called is the procedure that image will use to obtain the 
		image, pscmp looks for the image command and inserts
		pop { decompress }
		before it.  The 'pop' command removes whatever procedure was
		on the stack and then '{ decompress }' (my command) is pushed
		on the stack in it's place.

		It does compression with the following four "codes":
		u - one character  follows, whos ascii value  will determine
		    how many "unique" hex pairs follow. 1-256   pairs.
		U - two characters follows, whos ascii values will determine
		    how many "unique" hex pairs follow. 257-65535 pairs.
		r - one character  follows, whos ascii value  will determine
		    how many times to "repeat" the hex pair that follows.
		R - one characters follows, whos ascii values will determine
		    how many times to "repeat" the hex pair that follows.
NOTES:
		* ranges for R and U could not be made to be 257-65792,
		  without splitting the runs into multiple strings,
		  since the largest string is 65335.
		* I attempted two ways of storing the length of unique and
		  repeating runs.
		  The first and most straight forward to interpret in
		  postscipt, was to store them as one or two characters whose
		  ascii value was then interpretted as an integer by using the
		  'currentfile read pop' sequence.
		  The second used two or four digit hex number to represent
		  the length of the run, and used the postscript command
		  sequence:

/charx2  2 string def
/charx4  4 string def
/hexnum2 5 string def
/hexnum4 7 string def
/hexnum2 (16#00) def
/hexnum4 (16#0000) def
/getcount	{ hexnum2 3 currentfile charx2 readstring pop
		  putinterval hexnum2 cvi } def
/getbigcount	{ hexnum4 3 currentfile charx4 readstring pop
		  putinterval hexnum4 cvi } def

		  which works by putting the hex number ,ie. 'fd', in a string
		  like '16#00' thus giving the string '16#fd' which the command
		  'cvi' interprets as 0xfd, or 253.

		  The later method was necessary because characters representing
		  serial port I/O controls, ie. '^D', '^S/^Q' were interpretted
		  by the printers I/O control and not pasted to the postscript
		  interpretter.
		  The former method did work however with Sun's Postscript
		  previewer "pageview version 3"
		* pscmp removes the comments and unnecessary white space (used
		  for readability) from decomp.header as it inserts it into the
		  postscript.

*******************************************************************************
Here is the script:

#!/usr/local/bin/perl
# A perl script to compress postscript images.

# Written by: 
# Steve Parker                    parker@mps.ohio-state.edu
# Dept of Chemistry               201 McPherson Labs
# Ohio State University           614-292-5042
# Columbus OH, 43210
#
# codes: u - small count   run of unique hex pairs
#	 U - big   count   run of unique hex pairs
#	 r - small count+1    repeated   hex pair
#	 R - big   count+1    repeated   hex pair
#	 a repeat last r or R. NOT SUPPORTED IN THIS PERL SCRIPT.
#
# formats: u cc    'hphp...'
#	   U CC CC 'hphp...'
#	   r cc    'hp'
#	   R CC CC 'hp'
#
# where: 1) spaces are not output
#	 2) uUrR are output literally
#	 3) cc   is a 2 digit hex number (0-255) and represents range (1-256)
#	 4) CCCC is a 4 digit hex number (0-65535) for a range (257-65535)
#	    if not for max size on postscript string would be  (257-65792)
#	 5) 'hp' is a hex digit pair from 'image' data.
 
$name = $0;
$name =~ s'.*/''; # remove path--like basename
$usage = "usage:\n$name [postscript_file_with_IMAGE_data]";

select(STDOUT); $|=1;

$biggest=65534;
$last="";
while (<>) {
  if ( /([^A-Fa-f\d\n])/ ) {
#   print "'$1' ->$_";
    if ($_ =~ /showpage/ || $_ =~ /grestore/ ) {
#
# FOUND a showpage or grestore so write out last repeating pair or unique run.
#
      if ($repeating) {
	# we didn't record the first pair in $repeating
	# so we needn't subtract 1.
#$num=$repeating-1;
	$num=$repeating;
        if ( $num <= 255 ) {
          #   case 2 small count repeat unit 2 hex digits.
          printf("r%02X%2s\n",$num,$last);
	  $r++;
        } else {
          #   case 3  big  count repeat unit 2 hex digits.
          printf("R%02X%02X%2s\n",int($num/256),($num%256),$last);
	  $R++;
        }
      } else {
	$unique_str.=$last;
	# we didn't yet record this last pair in $unique_run
	# so we needn't subtract 1.
	$num=$unique_run;
        if ( $num <= 255 ) {
          # case 0 small count unique string of hex digit pairs.
          printf("u%02X%s",$num,$unique_str);
	  $u++;
        } else {
          # case 1  big  count unique string of hex digit pairs.
          printf("\nU%02X%02X%s",int($num/256),($num%256),$unique_str);
	  $U++;
        }
      }
      & end;
    }
# add the postscript decompression header
# inbetween the original proc called by the 'image' command
# and the 'image' command itself
    if ( $_ =~ /^(image\s?.*)$|^([^%]*)?(\simage\s?.*)$/ ) {
      print "$1\n" if ($1);
      if ($headerin) {
        $file="/home/sysadmin/postscript/compress/decomp.header";
#       open(HEADER,"$file") || die("$name: Cannot open $file: '$!'\n");
        while (<DATA>) { s/(\s)\s+/\1/g; print if !(/^%/); }
        $headerin++;
        close(DATA);
      } else {
	print " pop { decompress } ";
      }
      print "$2";
      next;
    }
    print;
    next;
  } # else { print "\n" if ($unique_run || $repeating); }
#
#--------------------   HEX PAIR HANDLING LOOP   --------------------------
#
  while (s?([A-F0-9a-f][A-F0-9a-f])??) {
    if ($repeating) {
      if ($1 eq $last) {
#-debug print STDERR "rs"; # repeating; same
        $repeating++;   # found another one.
	# check to see if we have filled biggest postscript string
	# this will kept the decompress in postscript simple and fast.
	if ($repeating eq $biggest) {
	  printf("Rfffe%2s",$last);
	  # set to start over fresh
	  $repeating=0;
	  # $unique_str should be set to null and $unique_run set to 0
	}
      } else {
#-debug print STDERR "rd"; # repeating; different
#
# FOUND a unique hex pair so repeating unit has ended, write it out.
#
#$num=$repeating-1;
	$num=$repeating;
        if ( $repeating <= 255 ) {
          #   case 2 small count repeat unit 2 hex digits.
# -line-  $line+=6; if ( $line > 80) { $line=6; print "\n"; }
#-debug   printf STDERR ">2,%2X,%2s ",$num,$last;
          printf("r%02X%2s",$num,$last);
	  $r++;
        } else {
          #   case 3  big  count repeat unit 2 hex digits.
# -line-  $line+=8; if ( $line > 80) { $line=8; print "\n"; }
#-debug   printf(">3,%2X,%2X,%2s ",int($num/256),($num%256),$last);
          printf("R%02X%02X%2s",int($num/256),($num%256),$last);
	  $R++;
        }
        $repeating=0;
        $last=$1;
      }

    } else { # must be unique'ing

      if ($1 eq $last) {
#-debug print "us"; # uniquing; same
#
# FOUND a repeating hex pair so might have a unique run
# which has ended, if so write it out.
#
        if ($unique_str) {
	  $num=$unique_run-1;
          if ( $num <= 255 ) {
            # case 0 small count unique string of hex digit pairs.
# -line-    $line+=(4+$unique_run)); if ( $line > 80) { $line=4+$unique_run; print "\n"; }
#-debug     printf("\n>0,%2X,'%s' ",$num,$unique_str);
            printf("\nu%02X%s",$num,$unique_str);
	    $u++;
          } else {
            # case 1  big  count unique string of hex digit pairs.
# -line-    $line+=(6+$unique_run); if ( $line > 80) { $line=6+$unique_run; print "\n"; }
#-debug     printf("\n>1,%2X,%2X,'%s' ",int($num/256),($num%256),
            printf("\nU%02X%02X%s",int($num/256),($num%256),$unique_str);
	    $U++;
          }
        }
        # start counting repeating pairs, reset unique_run count
        # and remember last.
        $repeating++;
        $unique_str='';$unique_run=0;
        $last=$1;
      } else { # countiue uniquing
#-debug print "ud"; # uniquing; different
        $unique_str.=$last;
#       $unique_run+=2; # use this if using $line to limit to 80 chars/line.
                        # but REMEMBER to divid by two when outputing!
        $unique_run++;
	# check to see if we have filled biggest postscript string
	# this will kept the decompress in postscript simple and fast.
	if ($unique_run eq $biggest) {
	  printf("Ufffe%s",$unique_str);
	  # set to start over fresh
          $unique_str='';$unique_run=0;
          $last=$1;
	  # $repeating should be set to 0
	}
        $last=$1;
      }
    }
  }
}
&end;
sub end {
  printf STDERR "Statistics:\n" ;
  printf STDERR "r's:%5d\n",$r ;
  printf STDERR "R's:%5d\n",$R ;
  printf STDERR "u's:%5d\n",$u ;
  printf STDERR "U's:%5d\n",$U ;
  ($user,$system,$cuser,$csystem)=times;
  printf STDERR "Times:\tuser,\tsystem,\tcuser,\tcsystem\n";
  printf STDERR "Times:\t%5f,\t%5f,\t%5f,\t%5f\n",
		 $user,$system,$cuser,$csystem;
  exit;
		 }
__END__
%-------------------------------------------------------------------------------
%
% header to define 'decompress' which will replace the
% { currentfile string readhexstring pop } proc commonly used with 'image'
%
% to be placed just before the 'image' command
% the 'pop' on the following line is to remove bogus 'proc' (as above)
pop
/repeater 1 string def
/char     1 string def
/charx2   2 string def
/charx4   4 string def
/hexnum2  5 string def
/hexnum4  7 string def
/debug   30 string def
/big  65535 string def
/hexnum2 (16#00)   def
/hexnum4 (16#0000) def
/gethexpair	{ currentfile char readhexstring pop } def
/getcount	{ hexnum2 3
		  currentfile charx2 readstring pop
		  putinterval hexnum2 cvi } def
/getbigcount	{ hexnum4 3
		  currentfile charx4 readstring pop
		  putinterval hexnum4 cvi } def
/codeu		{ pop /cnt getcount def
                  big 0 1 cnt { gethexpair putinterval big } for
                  0 cnt 1 add getinterval
		 } def
/codeU		{ pop /cnt getbigcount def
                  big 0 1 cnt { gethexpair putinterval big } for
                  0 cnt 1 add getinterval
		 } def
/coder		{ pop /cnt getcount    def
		  /repeater gethexpair def % get repeater unit
                  big 0 1 cnt {repeater putinterval big} for
		  0 cnt 1 add getinterval
		} def
/codeR		{ pop /cnt getbigcount def
		  /repeater gethexpair def % get repeater unit
                  big 0 1 cnt {repeater putinterval big} for
		  0 cnt 1 add getinterval
                } def
/codeX		{ pop big 0 cnt 1 add getinterval } def
/done		{ currentfile debug readstring pstack exit } def
/skip		{ pop decompress } def
#
# the following order of r,u,R,U was chosen by noting the frequency
# of occurance from a small number of examples but can easily be changed.
/others0	{ dup (u)  eq { codeu } { others1 } ifelse } def
/others1	{ dup (R)  eq { codeR } { others2 } ifelse } def
/others2	{ dup (U)  eq { codeU } { others3 } ifelse } def
/others3	{ dup (a)  eq { codeX } { others4 } ifelse } def
/others4	{ dup (\n) eq { skip  } {  done   } ifelse } def
/decompress	{ currentfile char readstring pop
		  dup (r)  eq { coder } { others0 } ifelse } def
{ decompress }
%-----------------------------------------------------------------------------
Newsgroups: comp.lang.postscript
Subject: postscript compression script in perl
Summary: 
Expires: 
Followup-To: 
Distribution: world
Organization: Department of Mathematics, The Ohio State University
Keywords: 

Newsgroups: comp.compression
Subject: Re: comp.compression Frequently Asked Questions (part 1/2)
Summary: 
Expires: 
Followup-To: 
Distribution: 
Organization: Department of Mathematics, The Ohio State University
Keywords: data compression, FAQ

In article <compr1_11aug92@chorus.fr> jloup@chorus.fr writes:
>Archive-name: compression-faq/part1
>Last-modified: Aug 11th, 1992
>
>This file is part 1 of a set of Frequently Asked Questions (FAQ) for
>the groups comp.compression and comp.compression.research.  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 <jloup@chorus.fr>.
>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.
>
>Main changes relative to the previous version: 
>
>- renumbered some questions to group together image compression subjects
>- included comp.compression.research (item 1)
>- corrected pointer to stuffit (item 2)
>- corrected pointer to Calgary text compression corpus (item 5)
>- added a few patent references -- to be checked for Fiala (item 8)
>- ccitt standards are no longer on ftp.uu.net (item 11)
>- added a pointer to more arithmetic coding sources (item 13)
>- added some references for fractal compression (item 17)
>- added pointer to H.261 spec (item 20)
>- added item 25: Fast DCT (Discrete Cosine Transform) algorithms
>- added pointers to a compression program for Sun audio files
>  and for a fast ADPCM algorithm (item 26)
>- discrete wavelet transforms are not slower than DCT (item 72)
>
>
>Contents
>========
>
>General questions:
>
>[1]  What are these newsgroups about?
>[2]  What is this .xxx file type?
>     Where can I find the corresponding compression program?
>[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.
>[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!
>
>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?
>
>(Long) introductions to data compression techniques (in part 2)
>
>[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
>
>[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, alt.graphics.pixutils). Please post your request
>in comp.compression only as a last resource.
>
>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.
>
>------------------------------------------------------------------------------
>
>Subject: [2] What is this .xxx file type?
>             Where can I find the corresponding compression program?
>
>
>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
>ux1.cso.uiuc.edu:/doc/pcnet/compression [128.174.5.59] maintained by
>David Lemson (lemson@uiuc.edu). When several programs can handle
>the same archive format, only one of them is given.
>
>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 terminator.cc.umich.edu:/atari/archivers [141.211.164.8]
>For Amiga, look on ab20.larc.nasa.gov:/amiga/utils/archivers  [128.155.23.64]
>	
>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 <jloup@chorus.fr>)
>
>ext:  produced by or read by
>
>.arc: arc, pkarc (MSDOS)
>	wuarchive.wustl.edu:/mirrors/msdos/starter/pk361.exe
>	garbo.uwasa.fi:/pc/arcers/pk361.exe
>
>      arc (Unix)
>        wuarchive.wustl.edu:/mirrors/misc/unix/arc521e.tar-z
>	garbo.uwasa.fi:/unix/arcers/arc.tar.Z
>        Contact: Howard Chu <hyc@umix.cc.umich.edu>
>
>      arc (VMS)
>	wuarchive.wustl.edu:/packages/compression/vax-vms/arc.exe
>
>      arcmac (Mac)
>	mac.archive.umich.edu:/mac/utilities/compressionapps/arcmac.hqx
>
>.arj: arj (MSDOS)
>        wuarchive.wustl.edu:/mirrors/msdos/arc-lbr/arj230.exe
>	garbo.uwasa.fi:/pc/arcers/arj230ng.exe
>
>      unarj (Unix). There is *no* arj for Unix. Don't post a request.
>        wuarchive.wustl.edu:/mirrors/misc/unix/unarj230.tar-z
>	garbo.uwasa.fi:/unix/arcers/unarj221.tar.Z
>      Contact: Robert K Jung <robjung@world.std.com>
>
>.cpt: Compact Pro (Macintosh)
>        sumex-aim.stanford.edu:/info-mac/util/compact-pro-132.hqx [36.44.0.6]
>
>.gif: gif files are images compressed with the LZW algorithm. See the
>      comp.graphics FAQ list for programs manipulating .gif files.
>
>.hqx: Macintosh BinHex format. (binhex is *not* a compression program, BTW.)
>       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]
>
>.lzh: lha (MSDOS)
>	wuarchive.wustl.edu:/mirrors/msdos/arc-lbr/lha213.exe
>	garbo.uwasa.fi:/pc/arcers/lha213.exe
>
>      lharc (Unix). 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
>
>      lha (Unix) Warning: all doc is in Japanese.
>	garbo.uwasa.fi:/unix/arcers/lha-1.00.tar.Z
>        ftp.kuis.kyoto-u.ac.jp:/utils/lha-1.00.tar.Z
>          Contact: lha-admin@oki.co.jp
>
>      lha (Mac)
>        mac.archive.umich.edu:/mac/utilities/compressionapps/maclha2.0.cpt.hqx
>
>      lharc (VMS). Same warning as for Unix lharc.
>	wuarchive.wustl.edu:/packages/compression/vax-vms/lharc.exe
>
>.pak: pak (MSDOS)
>        wuarchive.wustl.edu:/mirrors/msdos/arc-lbr/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]
>
>.sea: self-extracting archive (Macintosh)
>         Run the file to extract it. You can also extract it with:
> 	 mac.archive.umich.edu:/mac/utilities/compressionapps/desea1.11.cpt.hqx
>
>.sit: Stuffit (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]
>
>.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
>
>.tar.Z, .tar-z, .taz: tar + compress
>      For Unix: zcat file.tar.Z | tar xvf -
>      Other OS: first uncompress (see .Z below) then untar (see .tar above)
>
>.zip: pkzip 1.10 (MSDOS).
>	From the PKWARE BBS (June 92): "PKZIP 2.0 is expected to be released
>            sometime in the next few months, as soon as possible".
>           Contact: pkware.inc@mixcom.com
>
>         wuarchive.wustl.edu:/mirrors/msdos/zip/pkz110eu.exe.
>         garbo.uwasa.fi:/pc/arcers/pkz110eu.exe.
>           Note: pkz110eu.exe is an 'export' version without encryption.
>         ux1.cso.uiuc.edu:/pc/exec-pc/pkz193a.exe [128.174.5.59]
>           Note: pkzip 1.93a is an alpha version.
>           pkz201.exe is a hacked (illegal) copy of pkz193a.exe
>           pkz220.exe is also a hack and contains a dangerous virus.
>
>      zip 1.0 and unzip 4.2 (Unix, MSDOS, VMS, OS/2)
>	 wuarchive.wustl.edu:/mirrors/misc/unix/zip10ex.zip
>	 wuarchive.wustl.edu:/mirrors/misc/unix/unzip42.tar-z
>         wuarchive.wustl.edu:/mirrors3/garbo.uwasa.fi/arcutil/zcrypt10.zip
>           Non US residents must get the encryption code from garbo (see below)
>	 garbo.uwasa.fi:/unix/arcers/zip10ex.zip
>	 garbo.uwasa.fi:/unix/arcers/unzip42.tar.Z.
>         garbo.uwasa.fi:/pc/arcutil/zcrypt10.zip  (encryption code)
>           Contact: zip-bugs@cs.ucla.edu
>
>      zip 1.0 and unzip 4.2 (Mac)
>         valeria.cs.ucla.edu:/info-zip/Mac/zip_uzip.hqx
>         sumex-aim.stanford.edu:/info-mac/util/unzip-42.hqx
>
>.zoo: zoo 2.10 (MSDOS)
>	 wuarchive.wustl.edu:/mirrors/msdos/zoo/zoo210.exe
>	 garbo.uwasa.fi:/pc/arcers/zoo210.exe
>
>      zoo 2.10 (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 (Mac)
> 	 mac.archive.umich.edu:/mac/utilities/compressionapps/maczoo.sit.hqx
>
>      Contact: Rahul Dhesi <dhesi@cirrus.com>
>
>.F: freeze (Unix)
>     wuarchive.wustl.edu:/usenet/comp.sources.misc/volume25/freeze/part0[1-2].Z
>     ftp.inria.fr:/system/arch-compr/freeze-2.3.2.tar.Z
>     Contact: Leonid A. Broukhis <leo@s514.ipmce.su>
>
>.Y: yabba (Unix, VMS, ...)
>  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 <brnstnd@nyu.edu>
>
>.Z: compress (Unix)
>      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 (MSDOS)
>	wuarchive.wustl.edu:/mirrors/msdos/compress/comp430[ds].zip
>	garbo.uwasa.fi:/pc/unix/comp430d.zip
>
>    compress (Macintosh)
>        sumex-aim.stanford.edu:/info-mac/util/maccompress-32.hqx
>
>------------------------------------------------------------------------------
>
>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.  Detailed benchmarks have been posted in
>comp.compression by Peter Gutmann <pgut1@cs.aukuni.ac.nz>.
>
>*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. Two programs (hpack and comp-2) 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/hpack75a.tar.Z
>- sirius.ucs.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 still have to add all decompression times.]
>
>       size     lzrw3a   compress    lharc    yabba     pkzip    freeze 
>version:                   4.0       1.02      1.0       1.10     2.3.2 
>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              5m09s
>user             0m25s     0m29s     4m29s     1m46s              4m04s
>sys              0m05s     0m10s     0m07s     0m18s              0m11s
>MSDOS:                                                   1m39s
>                        
>	zip      zoo	   lha       arj      pkzip     hpack    comp-2   
>        1.0     2.10    1.0(Unix)   2.30      1.93a     0.75a	   
>	 -9      ah    2.13(MSDOS)   -jm       -ex      		 
>       ------  ------	 ------	   ------    ------    ------   ------
>bib	40717   40742	  40740	    36090     35186     35619    29840  
>book1  339932  339076	 339074	   318382    313566    306876   237380  
>book2  229419  228444	 228442	   210521    207204    208486   174085  
>geo	69837   68576	  68574	    69209     68698     58976    64590  
>news   154865  155086	 155084	   146855    144954    141608   128047  
>obj1	10522   10312	  10310	    10333     10307     10572    10819  
>obj2	86661   84983	  84981	    82052     81213     80806    85465  
>paper1	19761   19678	  19676	    18710     18519     18607    16895  
>paper2	32296   32098	  32096	    30034     29566     29825    25453  
>pic	56828   52223	  52221	    53578     52777     51778    55461  
>progc	13955   13943	  13941	    13408     13363     13475    12896  
>progl	16954   16916	  16914	    16408     16148     16586    17354  
>progp	11558   11509	  11507	    11308     11214     11647    11668  
>trans	22737   22580	  22578	    20046     19808     20506    21023  
>    1,106,013 1,096,166 1,096,138 1,036,934 1,022,523 1,005,367  890,976
>real    3m28s   4m07s     6m03s                       1h22m17s  27m05s
>user    1m45s   3m47s	  4m23s      		      1h20m46s  19m27s
>sys     0m11s   0m04s	  0m08s      		         0m12s   2m03s
>MSDOS:                    1m49s     2m41s     1m55s
>
>Notes:
>- zip 2.0 is not included in this comparison since it will be released
>  only when pkzip 2.0 is released. (Compression is comparable to that of
>  pkzip 1.93a.)
>
>- 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).
>
>- hpack 0.75a gives slightly different results on SunOS (undeterministic
>  behaviour still under investigation).
>
>- the MSDOS versions are all optimized with assembler code and were run
>  on a RAM disk. So it is not surprising that they 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.
>
>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.
>
>- The Gibson & Graybill patent 5,049,881 is the most general.
>  Claims 4 and 12 cover about any LZ algorithm using hashing, and could
>  even be interpreted as applying to the LZ78 family. (See below,
>  "Introduction to data compression" for the meaning of 'LZ').
>
>     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
>  covers any dictionary technique of the LZ family.
>
>- 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.
>
>- The LZW algorithm used in 'compress' is patented by IBM (4,814,746)
>  and Unisys (4,558,302). Unisys has licensed it for use in the V.42bis
>  compression standard. (See question 11 on V.42bis below.)
>
>- AP coding is patented by Storer (4,876,541). (Get the yabba package
>  for source code, see question 2 above, file type .Y)
>
>- Fiala and Greene have a patent (4,906,991?) on the algorithms they
>  published in Comm.ACM, April 89. One of their algorithms is used in lha
>  and zoo, and was used in zip 0.8.
>
>- IBM patented (5,001,478) the idea of combining a history buffer (the
>  LZ77 technique) and a lexicon (as in LZ78).
>
>- IBM holds a patent on the Q-coder implementation of arithmetic
>  coding.  The arithmetic coding option of the JPEG standard requires
>  use of the patented algorithm. (See the JPEG FAQ for details.)
>
>
>Here are some references on data compression patents, taken from the
>list maintained by Michael Ernst <mernst@theory.lcs.mit.edu> in
>mintaka.lcs.mit.edu:/mitlpf/ai/patent-list (or patent-list.Z).
>
>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
>
>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 ftp.uu.net as pub/lzw-patent.Z
>
>4,814,746
>Data compression method
>inventors Victor S. Miller, Mark N. Wegman
>assignee IBM
>filed 8/11/86, granted 3/21/89
>
>4,876,541
>Stem [sic] for dynamically compressing and decompressing electronic data
>inventor James A. Storer
>assignee Data Compression Corporation
>filed 10/15/87, granted 10/24/89
>
>4,955,066
>Compressing and Decompressing Text Files
>inventor Notenboom, L.A.
>assignee Microsoft
>filed  10/13/89, granted 09/04/90
>
>5,001,478
>Method of Encoding Compressed Data
>filed 1989-12-28
>granted 1991-03-19
>inventor Michael E. Nagy
>assignee IBM
>
>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
>cites McIntosh 3,914,586, Johannesson 4,087,788, Eastman 4,464,650,
>      Finn 4,560,976, Tsukiyama 4,586,027, 4,758,899 and 4,872,009,
>      Kunishi 4,677,649, Mathes 4,682,150, Shimoni 4,809,359, Miller 4,814,746,
>      Mukherjee 4,853,696, Fiala 4,906,991.
>
>5,051,745
>String searcher, and compressor using same
>inventor  Phillip W. Katz (author of pkzip)
>filed  8/21/90, granted 9/24/91
>cites MacCrisken 4,730,348 and Hong 4,961,139
>
>Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595.
>inventors Fiala,E.R., and Greene,D.H.
>
>------------------------------------------------------------------------------
>
>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 algorihtm used by DataFiles/16
>   is not subject to the laws of information theory. [...]
>
>
>(b) First details, by John Wallace <buckeye@spf.trw.com>:
>
>I called WEB at (404)514-8000 and they sent me some product
>literature as well as chatting for a few minutes with me on the phone.
>Their product is called DataFiles/16, and their claims for it are
>roughly those heard on the net.
>
>According to their flier:
>
>"DataFiles/16 will compress all types of binary files to approximately
>one-sixteenth of their original size ... regardless of the type of
>file (word processing document, spreadsheet file, image file,
>executable file, etc.), NO DATA WILL BE LOST by DataFiles/16."
>(Their capitalizations; 16:1 compression only promised for files >64K
>bytes in length.)
>
>"Performed on a 386/25 machine, the program can complete a
>compression/decompression cycle on one megabyte of data in less than
>thirty seconds"
>
>"The compressed output file created by DataFiles/16 can be used as the 
>input file to subsequent executions of the program.  This feature of 
>the utility is known as recursive or iterative compression, and will 
>enable you to compress your data files to a tiny fraction of the 
>original size.  In fact, virtually any amount of computer data can 
>be compressed to under 1024 bytes using DataFiles/16 to compress its 
>own output files muliple times.  Then, by repeating in reverse the 
>steps taken to perform the recusive compression, all original data 
>can be decompressed to its original form without the loss of a single 
>bit."
>
>They had a table that showed the expected size of resulting files,
>with the warning that "Your actual compresion results may vary
>slightly from the figures shown".  Here is my abridged version of their
>table. 
>		---------- Iteration -------
>INPUT		1	2	3 	4		Ratio
>1K		630					1.6:1
>16K		1.5K	812				20:1
>64K		4K	1K	644			101:1
>512K		30K	2K	938			558:1
>8M		490K	14K	1.5K	798		10512:1
>64M		3M	40K	3K	994		67513:1
>
>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 <rafael.ramirez@channel1.com>:
>
>   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. [...]
>
>   Mr. Bradley went on to say that Web will not be sending out any
>more copies to magazines and that they had even recalled the copy they
>had sent to Byte.  He claimed that he told the guy at Byte that the
>version they had at the time had just been translated to assembler and
>had some bugs, but that the guy at Byte kept insisting that they send
>a copy anyway, and so of course the version Byte had didn't work.
>
>[Correction from Russ Schnapp <rschnapp@metaflow.com>:
>Contrary to WEB's claim, I did NOT insist that WEB send me a
>non-functional copy of the program. I didn't even ask for the latest
>version.]
>
>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.
>
>   He said they will be sending out copies to about seven companies
>that want to license the technology for various applications but he
>could not give out any names due to non-disclosure agreements.  He
>hoped that in about two weeks he will be able to make an announcement
>and said he would call me when he could provide independent
>verification that the algorithm works.  For now, we can only wait.
>
>   He also said they have not as yet sold anything, but that he's
>been traveling constantly for the last three weeks (presumably to
>the seven companies he mentioned) and that he hasn't slept very
>well lately just thinking about all the applications the algorithm
>could be applied to.
>
>   And he confirmed that each pass will get 16:1 compression as
>long as the data is >64K, and that regardless, any file should be
>able to be compressed to less than 1024 bytes after enough passes.
>I asked if he is claiming that they can compress ANY data including
>data that is already compressed, and he just answered by saying
>that they had tested the program by compressing PKZIP files, and
>other files and that they all compressed as claimed (which of course
>still doesn't answer the question).
>
>
>(d) The interpretation of the claims
>
>The biggest controversy is over the claim to compress "all types of
>files".  As noted above by Rafael Ramirez, we do not know with
>certainty if WEB claims to compress *all* files greater than 64K
>bytes, or just *most* files. The WEB flier only says all *types* of
>files, not *all* files.  Keep this in mind when reading the
>impossibility proof given below.
>
>
>(e) 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. So at least two
>different input files must compress to the same output file. (Actually
>at least half of them, but two suffice for the proof.) Hence the
>compression program cannot be lossless.
>
>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.)
>
>
>(f) Late news: no software version
>
>Appeared on BIX, reposted by Bruce Hoult <Bruce.Hoult@actrix.gen.nz>:
>
>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. [...]
>
>
>(g) Conclusion
>
>Most readers of comp.compression are tired of this thread.  Please,
>please, do not post another article "I know this has been beaten to
>death, but...".
>
>The consensus is that we have to wait until WEB delivers a real product
>which can be independently tested. Only then will it be possible
>to know exactly what the product can and cannot do.
>
>[See also question 73 "What is the theoretical compression limit?" in
>part 2 of this FAQ.]
>
>------------------------------------------------------------------------------
>
>Subject: [11] What is the V.42bis standard?
>
>
>from Alejo Hausner <hausner@qucis.queensu.ca>:
>
>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 are available by ftp on src.doc.ic.ac.uk,
>in directory doc/ccitt-standards/ccitt. The v42bis standard is in
>/doc/ccitt-standards/ccitt/1992/v/v42bis.asc.Z.
>(ccitt standards used to be on ftp.uu.net in /doc/standards/ccitt
>but this directory is now empty -- Aug 11th.)
>
>------------------------------------------------------------------------------
>
>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 -ad ddjcompr" to get correct end-of-lines
>and recreate the directory structure. Five of the 6 programs are not
>portable and only run on MSDOS.
>
>------------------------------------------------------------------------------
>
>Subject: [13] I need source for arithmetic coding
>
>
>(See question 70 for an introduction to arithmetic coding.)
>
>Kris Popat <popat@image.mit.edu> has worked on "Scalar Quantization
>with Arithmetic Coding."  It describes an arithmetic coding technique
>which is quite general and computationally inexpensive.  The
>documentation and example C code are available via anonymous ftp from
>media-lab.media.mit.edu (18.85.0.2), in /pub/k-arith-code.
>
>See also the directory /pub/arithmetic.coding on fsa.cpsc.ucalgary.ca
>[136.159.2.1].
>
>------------------------------------------------------------------------------
>
>Subject: [15] Where can I get image compression programs?
>
>
>JPEG:
>      Source code for most any machine:
>      ftp.uu.net:/graphics/jpeg/jpegsrc.v3.tar.Z [137.39.1.9]
>      nic.funet.fi:/pub/graphics/programs/jpeg/jpegsrc.v3.tar.Z [128.214.6.100]
>      Contact: jpeg-info@uunet.uu.net (Independent JPEG Group)
>
>      xv, an image viewer which can read JPEG pictures, is available in
>      ftp.cicb.fr:/pub/X11R5/contrib/xv-2.20.tar.Z  [129.20.128.2]
>
>epic:
>      whitechapel.media.mit.edu:/pub/epic.tar.Z [18.85.0.125]
>      The "Lenna" test image is available as part of the EPIC package,
>      where it is named "test_image".
>
>compfits:
>      uwila.cfht.hawaii.edu:/pub/compfits/compfits.tar.Z  [128.171.80.50]
>      Contact: Jim Wright <jwright@cfht.hawaii.edu>
>
>fitspress:
>      128.103.40.79:/pub/fitspress08.tar.Z
>
>tiff:
>      For source and sample images, see question 18 below.
>
>------------------------------------------------------------------------------
>
>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 54 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.
>
>------------------------------------------------------------------------------
>
>Subject: [17] What is the state of fractal compression?
>
>
>from Tal Kubo <kubo@zariski.harvard.edu>:
>
>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 <srt@duke.cs.duke.edu> 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.
>
>
>There is a fractal image compression demo program  available via anonymous
>ftp in lyapunov.ucsd.edu:/pub/fractal_image_processing/all.tar.Z.
>There are executables and sample images in the same directory.
>
>References:
>  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. Jacquin, A Fractal Theory of Iterated Markov Operators with
>    Applications to Digital Image Coding, PhD Thesis, Georgia Tech, 1989.
>  A.E. Jacquin, 'A novel fractal block-coding technique for digital
>    images', Proc. ICASSP 1990.
>  A. Jacquin, 'Fractal image coding based on a theory of iterated
>    contractive image transformations', Visual Comm. and Image
>    Processing, vol SPIE-1360, 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).
>
>
>Barnsley's company is:
>
>Iterated Systems, Inc.
>5550A Peachtree Parkway, Suite 545
>Norcross, GA  30092
>404-840-0728
>404-840-0029 (fax)
>
>------------------------------------------------------------------------------
>
>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 spec is in ccitt/1988/ascii/7_3_01.txt.Z, the T.6 spec
>is in 7_3_02.txt.Z.
>
>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/v3.0beta.tar.Z     [192.48.153.1]
>    Contact: sam@sgi.com
>
>There is also a companion compressed tar file (v3.0pics.tar.Z) that
>has sample TIFF image files. A draft of TIFF 6.0 is in TIFF6.ps.Z.
>
>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.
>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.)
>
>A good introduction to JPEG is posted regularly in news.answers by
>Tom Lane <tgl+@cs.cmu.edu>. (See question 53 "Where are FAQ lists archived"
>if this posting has expired at your site.)
>
>------------------------------------------------------------------------------
>
>Subject: [20] I am looking for source of an H.261 codec.
>
>
>The H.261 spec is available on src.doc.ic.ac.uk in
>/doc/ccitt-standards/ccitt/1992/h/h261.doc.Z (or h261.rtf.Z)
>
>
>from Thierry TURLETTI <turletti@sophia.inria.fr>:
>
>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".
>
>------------------------------------------------------------------------------
>
>Subject: [25] Fast DCT (Discrete Cosine Transform) algorithms
>
>
>Here are some references provided by Tom Lane <tgl+@cs.cmu.edu>:
>
>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 Rao & Yip book cited in the jpeg v3 DCT code (see item 15 above) is a
>good overall introduction, with an extensive (though now dated) bibliography.
>
>------------------------------------------------------------------------------
>
>Subject: [26] Are there algorithms and standards for audio compression?
>
>
>Yes. See the introduction to MPEG given in part 2 of this FAQ.
>
>A compression program for Sun audio files (.au) is available by anonymous
>ftp as svr-ftp.eng.cam.ac.uk:/pub/misc/shorten-0.2.shar.
>
>
>Copied from the comp.dsp FAQ posted by guido@cwi.nl (Guido van Rossum):
>
>Strange though it seems, audio data is remarkably hard to compress
>effectively.  For 8-bit data, a Huffman encoding of the deltas between
>successive samples is relatively successful.  For 16-bit data,
>companies like Sony and Philips have spent millions to develop
>proprietary schemes.
>
>Public standards for voice compression are slowly gaining popularity,
>e.g. CCITT G.721 and G.723 (ADPCM at 32 and 24 kbits/sec).  (ADPCM ==
>Adaptive Delta Pulse Code Modulation.)  Free source code for a *fast*
>32 kbits/sec ADPCM algorithm is available by ftp from ftp.cwi.nl as
>/pub/adpcm.shar.
>
>
>There are also two US federal standards, 1016 (Code excited linear
>prediction (CELP), 4800 bits/s) and 1015 (LPC-10E, 2400 bits/s).  See
>also the appendix for 1016.
>
>(Note that U-LAW and silence detection can also be considered
>compression schemes.)
>
>------------------------------------------------------------------------------
>
>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 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 1.10 or unzip 4.2 (see question
>2 above for ftp sites).
>
>Immediately after zip 1.0 was released, a new undocumented feature
>of pkunzip was discovered, which causes CRC errors even with pkunzip 1.10
>on rare occasions. A patch is available on valeria.cs.ucla.edu in
>/pub/zip10.patch.
>
>------------------------------------------------------------------------------
>
>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: [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.
>(However, some versions of tar have the capability to 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 <rpw3@sgi.com>).
>
>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;
>        }
>}
>
>------------------------------------------------------------------------------
>
>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 pit-manager.mit.edu
>(18.72.1.58) and by email from mail-server@pit-manager.mit.edu (send
>a message containing "help" for instructions about the mail server).
>
>This posting is /pub/usenet/news.answers/compression-faq/part1.
>Part 2 is in (guess?) compression-faq/part2.
>
>------------------------------------------------------------------------------
>
>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.
>
>------------------------------------------------------------------------------
>
>Subject: [55] Where can I find Lenna and other images?
>
>
>A bunch of standard images (lenna, baboon, cameraman, crowd, moon
>etc..)  were on ftp site gauss.eedsp.gatech.edu (130.207.226.2) in
>directory /database/images. On Apr 1st, the system manager said:
>this site has had some hardware problems and will have the image
>database back online as soon as the problems get corrected. However
>the images are still not there (June 4th).
>
>The site ftp.ipl.rpi.edu also has standard images, in two directories:
>   ftp.ipl.rpi.edu:/pub/image/still/usc 
>   ftp.ipl.rpi.edu:/pub/image/still/canon
>
>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
>   ftp.ipl.rpi.edu:/pub/image/still/usc/color/lena  # 24 bit RGB
>   ftp.ipl.rpi.edu:/pub/image/still/usc/bgr/lena    # 24 bit BGR
>   ftp.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 rodney@ipl.rpi.edu.
>
>The archive maintainer at ftp.ipl.rpi.edu is interested in some method
>of establishing a canonical ftp database of images and could volunteer
>the ipl to be an ftp site for that database. Send suggestions to
>rodney@ipl.rpi.edu.
>
>
>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.
>
>          End of part 1 of the comp.compression faq.

To Whom It May Concern,

A few months ago I posted a request to the net regarding a postscript
compression routine.  I have since found out that Postscript 2 is to have
it's own standard way to compress images, nevertheless I have written a
postscript image compressor.

The postscript compressor I have written is in perl but the form of compression
is run-length encoding, and could be written in other languages, such as C, sed,
awk, nawk, etc. (I am sure that Larry could probably even write the thing in
roff--the man is mutant! ceveat: I am forever in his debt for writting perl.)

The most common responce that I received when telling my peers of my plans was
"Why write the thing in postscript?" or "Why write the thing at all?"

Everyone knows that the way screen dump/image capture routines output their
results on various architures is straight forward but disk wasteful.  Computer
screen images are not like images from other sources in that they almost always
have huge amounts of repetition, large areas all the same pattern.  And are
therefore very susceptible to run-length-encoding-type compression schemes.

The reasons I think that a compression routine written in postscript is valuable
are that the resulting compressed image is still a valid posctscript program,
which can be sent via E-mail without fear of corruption to anyone with a
postscript printer regardless of the machine to which it is connected, and
futhermore can be subsequently compressed with your favorite routine:
compress, pack, zip, zoo, arc, etc.

Finally I realize that this is not the most efficient method, but before I work
on enhancing it, I thought that I'd post it.  I would like your input on how to
improve it and I thought that many of you could use it 'as is' to help with
disk space problems (a never-ending problem at our site at least).  I have found
that users mind this form of compression less since it requires no additional
actions to print the file later.

If you use this package, I would appreciate timing results/comments/suggestions.
Please E-mail me any posts that you might make concerning this post so that
I will post a summary at a later date:

 Steve Parker                    parker@mps.ohio-state.edu
 Dept of Chemistry               201 McPherson Labs
 Ohio State University           614-292-5042

I have thought of many ways to improve this script:

1) Record which and how many of the decompression routines were used in a given
   image, and insert only those that were used and in the order of fequency
   that they were used.
2) Search the unique runs for patterns of 2 4 or 8 characters.
3) Make a new decompression routine called I for insert which would be used for
   inserting unique string into a long run of repeating characters.

NOTE: The above ideas would most easily be accomplished by saving the compressed
      image in memory or a temp file and/or making multiple passes at the image
      data.

Any other suggestions?

Here are timing results for postscript images created on various machines,
compressed on a Sparc ELC and printed on a AppleLaserWriter II:


Test cases:

					   		 (Apple LaserWriter II)
Filename	size in	chars	  bits in	time to     approximate time
                	     	   image	compress	 to print
-------------------------------------------------------------------------
snapshot.cmp.ps    63861	     ---	 67.0 s  	  100 s
snapshot.ps	  262906	   1024000	    --		  245 s
stripes.cmp.ps	    2241	     ---	 31.0 s		   30 s
stripes.ps	  133403	   1036800	    --  	  130 s
iris.cmp.ps	   73384   	     ---	 68.5 s		  100 s
iris.ps		  261385	    524288	    --  	  250 s
stellar.cmp.ps	  129140	     ---	 1027.3 s 	  425 s
stellar.ps	 1968436	   1966728	    --  	 1740 s

I am presently getting results for NeXT printers, and some others.

These files are available by E-mail at request to above address.

Here is my description of the two pieces necessary for
compression/decompression (I originally had two files but now use the <DATA>
file handle of perl):

decomp.header	is the postscript decompression header that will be used in
		place of
		"/picstr 1024 string def
		 { currentfile /picstr readhexstring pop }"
		which is often used as the proc for the image function
		ie "width hieght bitpersample proc image"

pscmp		is the perl script that compresses the hex digit pair
		format often used to encode a bitmap in postscript, it also
		inserts the decompression header file in a clever way.
		Since the last thing on the stack before the image command
		is called is the procedure that image will use to obtain the 
		image, pscmp looks for the image command and inserts
		pop { decompress }
		before it.  The 'pop' command removes whatever procedure was
		on the stack and then '{ decompress }' (my command) is pushed
		on the stack in it's place.

		It does compression with the following four "codes":
		u - one character  follows, whos ascii value  will determine
		    how many "unique" hex pairs follow. 1-256   pairs.
		U - two characters follows, whos ascii values will determine
		    how many "unique" hex pairs follow. 257-65535 pairs.
		r - one character  follows, whos ascii value  will determine
		    how many times to "repeat" the hex pair that follows.
		R - one characters follows, whos ascii values will determine
		    how many times to "repeat" the hex pair that follows.
NOTES:
		* ranges for R and U could not be made to be 257-65792,
		  without splitting the runs into multiple strings,
		  since the largest string is 65335.
		* I attempted two ways of storing the length of unique and
		  repeating runs.
		  The first and most straight forward to interpret in
		  postscipt, was to store them as one or two characters whose
		  ascii value was then interpretted as an integer by using the
		  'currentfile read pop' sequence.
		  The second used two or four digit hex number to represent
		  the length of the run, and used the postscript command
		  sequence:

/charx2  2 string def
/charx4  4 string def
/hexnum2 5 string def
/hexnum4 7 string def
/hexnum2 (16#00) def
/hexnum4 (16#0000) def
/getcount	{ hexnum2 3 currentfile charx2 readstring pop
		  putinterval hexnum2 cvi } def
/getbigcount	{ hexnum4 3 currentfile charx4 readstring pop
		  putinterval hexnum4 cvi } def

		  which works by putting the hex number ,ie. 'fd', in a string
		  like '16#00' thus giving the string '16#fd' which the command
		  'cvi' interprets as 0xfd, or 253.

		  The later method was necessary because characters representing
		  serial port I/O controls, ie. '^D', '^S/^Q' were interpretted
		  by the printers I/O control and not pasted to the postscript
		  interpretter.
		  The former method did work however with Sun's Postscript
		  previewer "pageview version 3"
		* pscmp removes the comments and unnecessary white space (used
		  for readability) from decomp.header as it inserts it into the
		  postscript.

*******************************************************************************
Here is the script:

#!/usr/local/bin/perl
# A perl script to compress postscript images.

# Written by: 
# Steve Parker                    parker@mps.ohio-state.edu
# Dept of Chemistry               201 McPherson Labs
# Ohio State University           614-292-5042
# Columbus OH, 43210
#
# codes: u - small count   run of unique hex pairs
#	 U - big   count   run of unique hex pairs
#	 r - small count+1    repeated   hex pair
#	 R - big   count+1    repeated   hex pair
#	 a repeat last r or R. NOT SUPPORTED IN THIS PERL SCRIPT.
#
# formats: u cc    'hphp...'
#	   U CC CC 'hphp...'
#	   r cc    'hp'
#	   R CC CC 'hp'
#
# where: 1) spaces are not output
#	 2) uUrR are output literally
#	 3) cc   is a 2 digit hex number (0-255) and represents range (1-256)
#	 4) CCCC is a 4 digit hex number (0-65535) for a range (257-65535)
#	    if not for max size on postscript string would be  (257-65792)
#	 5) 'hp' is a hex digit pair from 'image' data.
 
$name = $0;
$name =~ s'.*/''; # remove path--like basename
$usage = "usage:\n$name [postscript_file_with_IMAGE_data]";

select(STDOUT); $|=1;

$biggest=65534;
$last="";
while (<>) {
  if ( /([^A-Fa-f\d\n])/ ) {
#   print "'$1' ->$_";
    if ($_ =~ /showpage/ || $_ =~ /grestore/ ) {
#
# FOUND a showpage or grestore so write out last repeating pair or unique run.
#
      if ($repeating) {
	# we didn't record the first pair in $repeating
	# so we needn't subtract 1.
#$num=$repeating-1;
	$num=$repeating;
        if ( $num <= 255 ) {
          #   case 2 small count repeat unit 2 hex digits.
          printf("r%02X%2s\n",$num,$last);
	  $r++;
        } else {
          #   case 3  big  count repeat unit 2 hex digits.
          printf("R%02X%02X%2s\n",int($num/256),($num%256),$last);
	  $R++;
        }
      } else {
	$unique_str.=$last;
	# we didn't yet record this last pair in $unique_run
	# so we needn't subtract 1.
	$num=$unique_run;
        if ( $num <= 255 ) {
          # case 0 small count unique string of hex digit pairs.
          printf("u%02X%s",$num,$unique_str);
	  $u++;
        } else {
          # case 1  big  count unique string of hex digit pairs.
          printf("\nU%02X%02X%s",int($num/256),($num%256),$unique_str);
	  $U++;
        }
      }
      & end;
    }
# add the postscript decompression header
# inbetween the original proc called by the 'image' command
# and the 'image' command itself
    if ( $_ =~ /^(image\s?.*)$|^([^%]*)?(\simage\s?.*)$/ ) {
      print "$1\n" if ($1);
      if ($headerin) {
        $file="/home/sysadmin/postscript/compress/decomp.header";
#       open(HEADER,"$file") || die("$name: Cannot open $file: '$!'\n");
        while (<DATA>) { s/(\s)\s+/\1/g; print if !(/^%/); }
        $headerin++;
        close(DATA);
      } else {
	print " pop { decompress } ";
      }
      print "$2";
      next;
    }
    print;
    next;
  } # else { print "\n" if ($unique_run || $repeating); }
#
#--------------------   HEX PAIR HANDLING LOOP   --------------------------
#
  while (s?([A-F0-9a-f][A-F0-9a-f])??) {
    if ($repeating) {
      if ($1 eq $last) {
#-debug print STDERR "rs"; # repeating; same
        $repeating++;   # found another one.
	# check to see if we have filled biggest postscript string
	# this will kept the decompress in postscript simple and fast.
	if ($repeating eq $biggest) {
	  printf("Rfffe%2s",$last);
	  # set to start over fresh
	  $repeating=0;
	  # $unique_str should be set to null and $unique_run set to 0
	}
      } else {
#-debug print STDERR "rd"; # repeating; different
#
# FOUND a unique hex pair so repeating unit has ended, write it out.
#
#$num=$repeating-1;
	$num=$repeating;
        if ( $repeating <= 255 ) {
          #   case 2 small count repeat unit 2 hex digits.
# -line-  $line+=6; if ( $line > 80) { $line=6; print "\n"; }
#-debug   printf STDERR ">2,%2X,%2s ",$num,$last;
          printf("r%02X%2s",$num,$last);
	  $r++;
        } else {
          #   case 3  big  count repeat unit 2 hex digits.
# -line-  $line+=8; if ( $line > 80) { $line=8; print "\n"; }
#-debug   printf(">3,%2X,%2X,%2s ",int($num/256),($num%256),$last);
          printf("R%02X%02X%2s",int($num/256),($num%256),$last);
	  $R++;
        }
        $repeating=0;
        $last=$1;
      }

    } else { # must be unique'ing

      if ($1 eq $last) {
#-debug print "us"; # uniquing; same
#
# FOUND a repeating hex pair so might have a unique run
# which has ended, if so write it out.
#
        if ($unique_str) {
	  $num=$unique_run-1;
          if ( $num <= 255 ) {
            # case 0 small count unique string of hex digit pairs.
# -line-    $line+=(4+$unique_run)); if ( $line > 80) { $line=4+$unique_run; print "\n"; }
#-debug     printf("\n>0,%2X,'%s' ",$num,$unique_str);
            printf("\nu%02X%s",$num,$unique_str);
	    $u++;
          } else {
            # case 1  big  count unique string of hex digit pairs.
# -line-    $line+=(6+$unique_run); if ( $line > 80) { $line=6+$unique_run; print "\n"; }
#-debug     printf("\n>1,%2X,%2X,'%s' ",int($num/256),($num%256),
            printf("\nU%02X%02X%s",int($num/256),($num%256),$unique_str);
	    $U++;
          }
        }
        # start counting repeating pairs, reset unique_run count
        # and remember last.
        $repeating++;
        $unique_str='';$unique_run=0;
        $last=$1;
      } else { # countiue uniquing
#-debug print "ud"; # uniquing; different
        $unique_str.=$last;
#       $unique_run+=2; # use this if using $line to limit to 80 chars/line.
                        # but REMEMBER to divid by two when outputing!
        $unique_run++;
	# check to see if we have filled biggest postscript string
	# this will kept the decompress in postscript simple and fast.
	if ($unique_run eq $biggest) {
	  printf("Ufffe%s",$unique_str);
	  # set to start over fresh
          $unique_str='';$unique_run=0;
          $last=$1;
	  # $repeating should be set to 0
	}
        $last=$1;
      }
    }
  }
}
&end;
sub end {
  printf STDERR "Statistics:\n" ;
  printf STDERR "r's:%5d\n",$r ;
  printf STDERR "R's:%5d\n",$R ;
  printf STDERR "u's:%5d\n",$u ;
  printf STDERR "U's:%5d\n",$U ;
  ($user,$system,$cuser,$csystem)=times;
  printf STDERR "Times:\tuser,\tsystem,\tcuser,\tcsystem\n";
  printf STDERR "Times:\t%5f,\t%5f,\t%5f,\t%5f\n",
		 $user,$system,$cuser,$csystem;
  exit;
		 }
__END__
%-------------------------------------------------------------------------------
%
% header to define 'decompress' which will replace the
% { currentfile string readhexstring pop } proc commonly used with 'image'
%
% to be placed just before the 'image' command
% the 'pop' on the following line is to remove bogus 'proc' (as above)
pop
/repeater 1 string def
/char     1 string def
/charx2   2 string def
/charx4   4 string def
/hexnum2  5 string def
/hexnum4  7 string def
/debug   30 string def
/big  65535 string def
/hexnum2 (16#00)   def
/hexnum4 (16#0000) def
/gethexpair	{ currentfile char readhexstring pop } def
/getcount	{ hexnum2 3
		  currentfile charx2 readstring pop
		  putinterval hexnum2 cvi } def
/getbigcount	{ hexnum4 3
		  currentfile charx4 readstring pop
		  putinterval hexnum4 cvi } def
/codeu		{ pop /cnt getcount def
                  big 0 1 cnt { gethexpair putinterval big } for
                  0 cnt 1 add getinterval
		 } def
/codeU		{ pop /cnt getbigcount def
                  big 0 1 cnt { gethexpair putinterval big } for
                  0 cnt 1 add getinterval
		 } def
/coder		{ pop /cnt getcount    def
		  /repeater gethexpair def % get repeater unit
                  big 0 1 cnt {repeater putinterval big} for
		  0 cnt 1 add getinterval
		} def
/codeR		{ pop /cnt getbigcount def
		  /repeater gethexpair def % get repeater unit
                  big 0 1 cnt {repeater putinterval big} for
		  0 cnt 1 add getinterval
                } def
/codeX		{ pop big 0 cnt 1 add getinterval } def
/done		{ currentfile debug readstring pstack exit } def
/skip		{ pop decompress } def
#
# the following order of r,u,R,U was chosen by noting the frequency
# of occurance from a small number of examples but can easily be changed.
/others0	{ dup (u)  eq { codeu } { others1 } ifelse } def
/others1	{ dup (R)  eq { codeR } { others2 } ifelse } def
/others2	{ dup (U)  eq { codeU } { others3 } ifelse } def
/others3	{ dup (a)  eq { codeX } { others4 } ifelse } def
/others4	{ dup (\n) eq { skip  } {  done   } ifelse } def
/decompress	{ currentfile char readstring pop
		  dup (r)  eq { coder } { others0 } ifelse } def
{ decompress }
%-----------------------------------------------------------------------------