CJB2(1) DjVuLibre-3.5 CJB2(1)NAMEcjb2 - Simple DjVuBitonal encoder.
SYNOPSIScjb2 [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 res‐
olution 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 argu‐
ment 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 unaccept‐
able character substitutions.
-verbose
Display informational messages while running.
REMARKS
Lossless encoding is competitive with that of the Lizardtech commercial
encoders.
Lossy encoding is making 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.source‐
forge.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 <den‐
nis@rkd.math.cornell.edu> and Paul Young.
SEE ALSOdjvu(1), pbm(5).
DjVuLibre-3.5 10/11/2001 CJB2(1)
