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BZZ(1)                           DjVuLibre-3.5                          BZZ(1)



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 com-
       pressed 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://cor-
       pus.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 Leon Bottou <leonbATusers.net> and was then improved by Andrei Erofeev
       <andrew_erofeevATyahoo.com>, Bill Riemers <docbillATsourceforge.net> and many others.


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



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