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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 usu- ally produces higher compression ratios and increases the memory re- quirements of both the encoder and decoder. It is useless to spec- ify 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 fre- quencies. 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 im- provement 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)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ALGORITHMS | PERFORMANCE | CREDITS | SEE ALSO
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