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  trans-
	      form  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  use-
	      less 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 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)