1CJB2(1)                          DjVuLibre-3.5                         CJB2(1)
2
3
4

NAME

6       cjb2 - Simple DjVuBitonal encoder.
7
8

SYNOPSIS

10       cjb2  [options] inputfile outputdjvufile
11
12

DESCRIPTION

14       This  is a simple encoder for bitonal files.  Argument inputfile is the
15       name of a PBM or bitonal TIFF file containing a single document  image.
16       This program produces a DjVuBitonal file named outputdjvufile.
17
18       The  default  compression process is lossless: decoding the DjVuBitonal
19       file at full resolution will produce an image exactly identical to  the
20       input  file.   Lossy  compression  is  enabled  by  options -losslevel,
21       -lossy, or -clean.
22
23

OPTIONS

25       -dpi n Specify the resolution information encoded into the output  file
26              expressed  in  dots per inch. The resolution information encoded
27              in DjVu files determine how the decoder scales the  image  on  a
28              particular  display.   Meaningful  resolutions  range from 25 to
29              1200.  The default resolution for TIFF files is  the  resolution
30              is the resolution specified by the input file.  The default res‐
31              olution for PBM files is 300 dpi.
32
33       -lossless
34              Ensure that the encoded image is pixel-per-pixel  equal  to  the
35              initial image.  This option is is equivalent to -losslevel 0 and
36              is the default.
37
38       -clean Only remove flyspecks from the input image.  This option enables
39              a heuristic algorithm that removes very small marks.  Such marks
40              are often causes by noise and dust during the scanning  process.
41              The  threshold  mark  size is chosen according to the resolution
42              specified with option This option is is equivalent to -losslevel
43              1.
44
45       -lossy Substitute  patterns  with small variations.  In addition to the
46              flyspeck removal heuristic, this  option  enables  an  algorithm
47              that  encodes certain characters by simply replicating the shape
48              of a previously encoded character with a  similar  shape.   This
49              option is is equivalent to -losslevel 100.
50
51       -losslevel x
52              Specify  the aggressiveness of the lossy compression.  Its argu‐
53              ment ranges from 0 to 200.  Higher values generate smaller files
54              with  more  potential  distortions.  Loss level 0 corresponds to
55              lossless encoding.  Loss level 1  performs  image  cleaning  but
56              does  not perform character substitution at all.  Loss level 100
57              is intended to provide a good compromise.   Higher  loss  levels
58              provide  marginally  better compression at the risk of unaccept‐
59              able character substitutions.
60
61       -verbose
62              Display informational messages while running.
63
64

REMARKS

66       Lossless encoding is competitive with that of the Lizardtech commercial
67       encoders.
68
69       Lossy  encoding has made much progress thanks to Ilya Mezhirov from the
70       minidjvu project.  This also means that the lossy encoding  performance
71       can  change  from  version  to  version.  When lossy compression yields
72       inadequate results, simply revert to only using option -clean or reduce
73       the parameter of option -losslevel.
74
75       Two features are still missing:
76
77       *  Half-tone  detection.  Collecting small marks belonging to half-tone
78          patterns would improve compression speed.
79
80       *  Multi-page compression. Matching characters on several  pages  would
81          improve the compression ratios for multi-page documents.
82
83

CREDITS

85       This  program was initially written by Léon Bottou <leonb@users.source‐
86       forge.net> and was improved by Bill  Riemers  <docbill@sourceforge.net>
87       and  many others.  The pattern matching algorithm for lossy compression
88       was contributed by Ilya Mezhirov <ilya@mezhirov.mccme.ru>.  TIFF  input
89       routines  are inspired by the ones contributed by R. Keith Dennis <den‐
90       nis@rkd.math.cornell.edu> and Paul Young.
91
92

SEE ALSO

94       djvu(1), pbm(5).
95
96
97
98DjVuLibre-3.5                     10/11/2001                           CJB2(1)
Impressum