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bzz(1) [debian man page]

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)

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CJB2(1) 							   DjVuLibre-3.5							   CJB2(1)

NAME
cjb2 - Simple DjVuBitonal encoder. SYNOPSIS
cjb2 [options] inputfile outputdjvufile DESCRIPTION
This is a simple encoder for bitonal files. Argument inputfile is the name of a PBM or bitonal TIFF file containing a single document image. This program produces a DjVuBitonal file named outputdjvufile. The default compression process is lossless: decoding the DjVuBitonal file at full resolution will produce an image exactly identical to the input file. Lossy compression is enabled by options -losslevel, -lossy, or -clean. OPTIONS
-dpi n Specify the resolution information encoded into the output file expressed in dots per inch. The resolution information encoded in DjVu files determine how the decoder scales the image on a particular display. Meaningful resolutions range from 25 to 1200. The default resolution for TIFF files is the resolution is the resolution specified by the input file. The default resolution for PBM files is 300 dpi. -lossless Ensure that the encoded image is pixel-per-pixel equal to the initial image. This option is is equivalent to -losslevel 0 and is the default. -clean Only remove flyspecks from the input image. This option enables a heuristic algorithm that removes very small marks. Such marks are often causes by noise and dust during the scanning process. The threshold mark size is chosen according to the resolution spec- ified with option This option is is equivalent to -losslevel 1. -lossy Substitute patterns with small variations. In addition to the flyspeck removal heuristic, this option enables an algorithm that encodes certain characters by simply replicating the shape of a previously encoded character with a similar shape. This option is is equivalent to -losslevel 100. -losslevel x Specify the aggressiveness of the lossy compression. Its argument ranges from 0 to 200. Higher values generate smaller files with more potential distortions. Loss level 0 corresponds to lossless encoding. Loss level 1 performs image cleaning but does not per- form character substitution at all. Loss level 100 is intended to provide a good compromise. Higher loss levels provide marginally better compression at the risk of unacceptable character substitutions. -verbose Display informational messages while running. REMARKS
Lossless encoding is competitive with that of the Lizardtech commercial encoders. Lossy encoding has made much progress thanks to Ilya Mezhirov from the minidjvu project. This also means that the lossy encoding perfor- mance can change from version to version. When lossy compression yields inadequate results, simply revert to only using option -clean or reduce the parameter of option -losslevel. Two features are still missing: * Half-tone detection. Collecting small marks belonging to half-tone patterns would improve compression speed. * Multi-page compression. Matching characters on several pages would improve the compression ratios for multi-page documents. CREDITS
This program was initially written by Leon Bottou <leonb@users.sourceforge.net> and was improved by Bill Riemers <docbill@sourceforge.net> and many others. The pattern matching algorithm for lossy compression was contributed by Ilya Mezhirov <ilya@mezhirov.mccme.ru>. TIFF input routines are inspired by the ones contributed by R. Keith Dennis <dennis@rkd.math.cornell.edu> and Paul Young. SEE ALSO
djvu(1), pbm(5). DjVuLibre-3.5 10/11/2001 CJB2(1)

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