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)