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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 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 |
+=============================================================================================================+
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 <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)