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NAME

       bzz - DjVu general purpose compression utility.

SYNOPSIS

   Encoding:
       bzz -e[blocksize] inputfile outputfile

   Decoding:
       bzz -d inputfile outputfile

DESCRIPTION

       The first form of the command line (option -e) compresses the data from
       file inputfile and writes the compressed  data  into  outputfile.   The
       second form of the command line (option -d) decompressed file inputfile
       and writes the output to outputfile.

OPTIONS

       -d     Decoding mode.

       -e[blocksize]
              Encoding mode.  The optional argument  blocksize  specifies  the
              size  of  the input file blocks processed by the Burrows-Wheeler
              transform expressed in kilobytes.  The default  block  sizes  is
              2048  KB.   The  maximal  block  size  is 4096 KB.  Specifying a
              larger block size usually produces higher compression ratios and
              increases  the  memory  requirements  of  both  the  encoder and
              decoder.  It is useless to specify a block size that  is  larger
              than the input file.

ALGORITHMS

       The  Burrows-Wheeler  transform is performed using a combination of the
       Karp-Miller-Rosenberg and the  Bentley-Sedgewick  algorithms.  This  is
       comparable  to (Sadakane, DCC 98) with a slightly more flexible ranking
       scheme. Symbols are then ordered according to  a  running  estimate  of
       their  occurrence frequencies.  The symbol ranks are then coded using a
       simple fixed tree and the ZP binary adaptive coder (Bottou, DCC 98).

       The Burrows-Wheeler transform is also used in the well known compressor
       bzip2.   The  originality  of  bzz is the use of the ZP adaptive coder.
       The adaptation noise can cost up to 5 percent in file  size,  but  this
       penalty is usually offset by the benefits of adaptation.

PERFORMANCE

       The  following  table shows comparative results (in bits per character)
       on the Canterbury Corpus ( http://corpus.canterbury.ac.nz ).  The  very
       good  bzz  performance  on  the spreadsheet file excl puts the weighted
       average ahead of much more sophisticated compressors such as fsmx.

┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
├─────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ fsmx        2.10   0.79   1.89   1.48   2.52   1.84   2.21   2.24   2.29   2.91   2.35     1.63      2.06   │
│ bzz         2.25   0.76   2.13   0.78   2.67   2.00   2.40   2.52   2.60   3.19   2.52     1.44      2.16   │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

       Note that  DjVu  contributors  have  several  entries  in  this  table.
       Program  compress was written some time ago by Joe Orost.  Program ppmd
       is an improvement of the PPM-C method invented by Paul Howard.

CREDITS

       Program bzz was written by  Léon  Bottou  <leonb@users.sourceforge.net>
       and  was  then  improved  by Andrei Erofeev <andrew_erofeev@yahoo.com>,
       Bill Riemers <docbill@sourceforge.net> and many others.

SEE ALSO

       djvu(1), compress(1), gzip(1), bzip2(1)



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