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ppmquant
!!!ppmquant
NAME
SYNOPSIS
DESCRIPTION
REFERENCES
SEE ALSO
AUTHOR
----
!!NAME


ppmquant - quantize the colors in a portable pixmap down to a specified number
!!SYNOPSIS


__ppmquant__ [[__-floyd__|__-fs__] ''ncolors''
[[''ppmfile'']__
ppmquant__ [[__-floyd__|__-fs__] __-map__
''mapfile'' [[''ppmfile'']
!!DESCRIPTION


Reads a portable pixmap as input. Chooses ''ncolors''
colors to best represent the image, maps the existing colors
to the new ones, and writes a portable pixmap as
output.


The quantization method is Heckbert's


Alternately, you can skip the color-choosing step by
specifying your own set of colors with the __-map__ flag.
The ''mapfile'' is just a ''ppm'' file; it can be any
shape, all that matters is the colors in it. For instance,
to quantize down to the 8-color IBM TTL color set, you might
use:


    P3
8 1
255
0   0   0
255   0   0
0 255   0
0   0 255
255 255   0
255   0 255
0 255 255
255 255 255
If you want to quantize one pixmap to use the colors in another one, just use the second one as the mapfile. You don't have to reduce it down to only one pixel of each color, just use it as is.


The __-floyd__/__-fs__ flag enables a Floyd-Steinberg
error diffusion step. Floyd-Steinberg gives vastly better
results on images where the unmodified quantization has
banding or other artifacts, especially when going to a small
number of colors such as the above IBM set. However, it does
take substantially more CPU time, so the default is
off.


All flags can be abbreviated to their shortest unique
prefix.
!!REFERENCES


!!SEE ALSO


ppmquantall(1), pnmdepth(1), ppmdither(1),
ppm(5)
!!AUTHOR


Copyright (C) 1989, 1991 by Jef Poskanzer.
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Last edited on Monday, June 3, 2002 6:50:59 pm by "perry"

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