Tribblix: manual page: cjb2.1

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 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