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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 con-
       taining 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  resolu-
              tion  information  encoded in DjVu files determine how the decoder scales the image on a particular dis-
              play.  Meaningful resolutions range from 25 to 1200.  The default resolution for TIFF files is the reso-
              lution  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  equiva-
              lent 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 specified 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 perform 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  performance 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  <leonbATusers.net>  and  was  improved  by  Bill
       Riemers  <docbillATsourceforge.net>  and  many others.  The pattern matching algorithm for lossy compression was
       contributed by Ilya Mezhirov <ilyaATmezhirov.ru>.  TIFF input routines  are  inspired  by  the  ones  con-
       tributed by R. Keith Dennis <dennisATrkd.edu> and Paul Young.


SEE ALSO
       djvu(1), pbm(5).



DjVuLibre-3.5                     10/11/2001                           CJB2(1)