NAME
cpaldjvu - DjVuDocument encoder for low-color images.
SYNOPSIS
cpaldjvu [options] inputppmfile outputdjvufile
DESCRIPTION
Program 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 GIF or 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.
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
6000. The default value is 300 dpi.
-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.
-bgwhite
Cause the background layer to use the lightest quantified color
instead of the dominant color.
-verbose
Display informational messages while running.
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 ppmquant. Avoid
using the error diffusion dithering algorithm. This algorithm
generates random dithering patterns that might be very costly to
encode.
BUGS
This program should be rewritten as a pre-processor for csepdjvu.
CREDITS
This program was initially written by Leon Bottou
<leonb@users.sourceforge.net> and was improved by Bill Riemers
<docbill@sourceforge.net> and many others.
SEE ALSO
djvu(1), pbm(5), ppmquant(1), pnmtogif(1), pnmtopng(1)