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.

   ┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
   │                                           Compression performance                                            │
   │              text   fax    csrc   excl   sprc   tech   poem   html   lisp   man    play   Weighted   Average │
   ├──────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
   │  compress    3.27   0.97   3.56   2.41   4.21   3.06   3.38   3.68   3.90   4.43   3.51     2.55      3.31   │
   │  gzip -9     2.85   0.82   2.24   1.63   2.67   2.71   3.23   2.59   2.65   3.31   3.12     2.08      2.53   │
   │  bzip2 -9    2.27   0.78   2.18   1.01   2.70   2.02   2.42   2.48   2.79   3.33   2.53     1.54      2.23   │
   │  ppmd        2.31   0.99   2.11   1.08   2.68   2.19   2.48   2.38   2.43   3.00   2.53     1.65      2.20   │
   │  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)

DjVuLibre-3.5                                      10/11/2001                                             BZZ(1)