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PROGRAM:

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 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 Léon 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.

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