Tribblix: manual page: cpaldjvu.1

CPALDJVU(1) DjVuLibre-3.5 CPALDJVU(1)

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 L'eon Bottou
<leonb@users.sourceforge.net> and was improved by Bill Riemers
<docbill@sourceforge.net> and many others.