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cpaldjvu(1) [debian man page]

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 val- ues 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 col- ors. 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) DjVuLibre-3.5 10/11/2001 CPALDJVU(1)

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CJB2(1) 							   DjVuLibre-3.5							   CJB2(1)

NAME
cjb2 - Simple DjVuBitonal encoder. SYNOPSIS
cjb2 [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 resolution 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 spec- ified 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 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 per- form 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. -verbose Display informational messages while running. REMARKS
Lossless encoding is competitive with that of the Lizardtech commercial encoders. Lossy encoding has made much progress thanks to Ilya Mezhirov from the minidjvu project. This also means that the lossy encoding perfor- mance 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 Leon 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. SEE ALSO
djvu(1), pbm(5). DjVuLibre-3.5 10/11/2001 CJB2(1)

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