.\" Copyright (c) 2001-2003 Leon Bottou, Yann Le Cun, Patrick Haffner,

.\" Copyright (c) 2001 AT&T Corp., and Lizardtech, Inc.

.\"

.\" This is free documentation; you can redistribute it and/or

.\" modify it under the terms of the GNU General Public License as

.\" published by the Free Software Foundation; either version 2 of

.\" the License, or (at your option) any later version.

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.\" and "executables" are to be interpreted as the output of any

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.\" This manual is distributed in the hope that it will be useful,

.\" but WITHOUT ANY WARRANTY; without even the implied warranty of

.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

.\" GNU General Public License for more details.

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.\" You should have received a copy of the GNU General Public

.\" License along with this manual. Otherwise check the web site

.\" of the Free Software Foundation at http://www.fsf.org.

.TH CJB2 1 "10/11/2001" "DjVuLibre-3.5" "DjVuLibre-3.5"

.SH NAME

cjb2 \- Simple DjVuBitonal encoder.

.SH SYNOPSIS

.BI "cjb2  [" "options" "] " "inputfile" " " "outputdjvufile"

.SH DESCRIPTION

This is a simple encoder for bitonal files.

Argument 

.I inputfile

is the name of a 

.SM PBM

or bitonal

.SM TIFF

file containing a single document image.

This program produces a DjVuBitonal file named

.IR 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

.BR -losslevel ,

.BR -lossy ,

or

.BR -clean .

.SH OPTIONS

.TP

.BI "-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 

.SM TIFF

files is the resolution is the resolution specified by the input file.

The default resolution for

.SM PBM

files is 300 dpi.

.TP

.B "-lossless"

Ensure that the encoded image is pixel-per-pixel equal

to the initial image. 

This option is is equivalent to 

.BR "-losslevel 0" 

and is the default.

.TP

.B "-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 

.BR "-losslevel 1" .

.TP

.B "-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 

.BR "-losslevel 100" .

.TP

.BI "-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. 

.TP

.B "-verbose"

Display informational messages while running.

.SH REMARKS

Lossless encoding is competitive with that of the 

Lizardtech commercial encoders. 

.PP

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

.BR -clean 

or reduce the parameter of option

.BR -losslevel .

.PP

Two features are still missing:

.IP "*" 3

Half-tone detection. Collecting small marks belonging 

to half-tone patterns would improve compression speed.

.IP "*" 3

Multi-page compression. Matching characters on several pages

would improve the compression ratios for multi-page documents.

.SH CREDITS

This program was initially written by L\('eon 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.

.SH SEE ALSO

.BR djvu (1),

.BR pbm (5).