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ppmquant.1
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ppmquant(1) USER COMMANDS ppmquant(1)
NAME
ppmquant - quantize the colors in a portable pixmap down to
a specified number
SYNOPSIS
ppmquant [-floyd|-fs] _✓n_✓c_✓o_✓l_✓o_✓r_✓s [_✓p_✓p_✓m_✓f_✓i_✓l_✓e]
ppmquant [-floyd|-fs] -map _✓m_✓a_✓p_✓f_✓i_✓l_✓e [_✓p_✓p_✓m_✓f_✓i_✓l_✓e]
DESCRIPTION
Reads a portable pixmap as input. Chooses _✓n_✓c_✓o_✓l_✓o_✓r_✓s 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 "median cut".
Alternately, you can skip the color-choosing step by speci-
fying your own set of colors with the -map flag. The _✓m_✓a_✓p_✓-
_✓f_✓i_✓l_✓e is just a _✓p_✓p_✓m 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
The -floyd/-fs flag enables a Floyd-Steinberg error diffu-
sion 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 pre-
fix.
REFERENCES
"Color Image Quantization for Frame Buffer Display" by Paul
Heckbert, SIGGRAPH '82 Proceedings, page 297.
SEE ALSO
pnmdepth(1), ppmquantall(1), ppm(5)
AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
Sun Release 4.0 Last change: 12 January 1991 1