1BZZ(1)                           DjVuLibre-3.5                          BZZ(1)
2
3
4

NAME

6       bzz - DjVu general purpose compression utility.
7
8

SYNOPSIS

10   Encoding:
11       bzz -e[blocksize] inputfile outputfile
12
13   Decoding:
14       bzz -d inputfile outputfile
15

DESCRIPTION

17       The  first  form  of  the command line (option -e ) compresses the data
18       from file inputfile and writes the  compressed  data  into  outputfile.
19       The  second  form  of  the  command line (option -d ) decompressed file
20       inputfile and writes the output to outputfile.
21
22

OPTIONS

24       -d     Decoding mode.
25
26       -e[blocksize]
27              Encoding mode.  The optional argument  blocksize  specifies  the
28              size  of  the input file blocks processed by the Burrows-Wheeler
29              transform expressed in kilobytes.  The default  block  sizes  is
30              2048  KB.   The  maximal  block  size  is 4096 KB.  Specifying a
31              larger block size usually produces higher compression ratios and
32              increases  the  memory  requirements  of  both  the  encoder and
33              decoder.  It is useless to specify a block size that  is  larger
34              than the input file.
35
36

ALGORITHMS

38       The  Burrows-Wheeler  transform is performed using a combination of the
39       Karp-Miller-Rosenberg and the  Bentley-Sedgewick  algorithms.  This  is
40       comparable  to (Sadakane, DCC 98) with a slightly more flexible ranking
41       scheme. Symbols are then ordered according to  a  running  estimate  of
42       their  occurrence frequencies.  The symbol ranks are then coded using a
43       simple fixed tree and the ZP binary adaptive coder (Bottou, DCC 98).
44
45       The Burrows-Wheeler transform is also used in the well known compressor
46       bzip2.   The  originality  of  bzz is the use of the ZP adaptive coder.
47       The adaptation noise can cost up to 5 percent in file  size,  but  this
48       penalty is usually offset by the benefits of adaptation.
49
50

PERFORMANCE

52       The  following  table shows comparative results (in bits per character)
53       on the Canterbury Corpus ( http://corpus.canterbury.ac.nz ).  The  very
54       good  bzz  performance  on  the spreadsheet file excl puts the weighted
55       average ahead of much more sophisticated compressors such as fsmx.
56
57
58┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
59│                                          Compression performance                                            │
60│             text   fax    csrc   excl   sprc   tech   poem   html   lisp   man    play   Weighted   Average │
61├─────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
62│ 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   │
63│ 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   │
64│ 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   │
65│ 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   │
66│ 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   
67bzz         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   │
68└─────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
69
70       Note that DjVu contributors have several entries in this  table.   Pro‐
71       gram  compress was written some time ago by Joe Orost.  Program ppmd is
72       an improvement of the PPM-C method invented by Paul Howard.
73
74

CREDITS

76       Program bzz was written by  Léon  Bottou  <leonb@users.sourceforge.net>
77       and  was  then  improved  by Andrei Erofeev <andrew_erofeev@yahoo.com>,
78       Bill Riemers <docbill@sourceforge.net> and many others.
79
80

SEE ALSO

82       djvu(1), compress(1), gzip(1), bzip2(1)
83
84
85
86DjVuLibre-3.5                     10/11/2001                            BZZ(1)
Impressum