File: cpaldjvu.1

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.\" 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.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" 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.
.\"
.\" 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 CPALDJVU 1 "10/11/2001" "DjVuLibre-3.5" "DjVuLibre-3.5"
.SH NAME
cpaldjvu \- DjVuDocument encoder for low-color images.

.SH SYNOPSIS
.BI "cpaldjvu  [" "options" "] " "inputppmfile" " " "outputdjvufile"

.SH DESCRIPTION
Program 
.B cpaldjvu
is a DjVuDocument encoder for images containing few colors.  It performs best
on images containing large solid color areas such as screen dumps.
Compression ratios on such images can be much higher than those achieved by
.SM GIF
or
.SM PNG
compression.

This program works by first reducing the number of distinct colors to a small
specified value using a simple color quantization algorithm.  The dominant
color is encoded into the background layer.  The other colors are encoded into
the foreground layer.

.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 6000.  The default value is 300 dpi.
.TP
.BI "-colors " "n"
Specify a maximum number of distinct colors for the color quantization
algorithm.  process. The default value is 256.  Smaller values can produce
much smaller files.
.TP
.B "-bgwhite"
Cause the background layer to use the lightest quantified color
instead of the dominant color.
.TP
.B "-verbose"
Display informational messages while running.

.SH REMARKS
The color quantization might introduce severe degradation if the image
contains photographic areas with a large number of very similar colors.
Color quantization problems might be solved by pre-processing
the input file with a different quantization program such as
.BR ppmquant .
Avoid using the error diffusion dithering algorithm.
This algorithm generates random dithering patterns that
might be very costly to encode.

.SH BUGS
This program should be rewritten as a pre-processor for 
.BR csepdjvu .

.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.

.SH SEE ALSO
.BR djvu (1),
.BR pbm (5),
.BR ppmquant (1),
.BR pnmtogif (1),
.BR pnmtopng (1)