ppmquant(1)						      General Commands Manual						       ppmquant(1)

NAME

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

SYNOPSIS

       ppmquant [-floyd|-fs] ncolors [ppmfile]
       ppmquant [-floyd|-fs] [-nofloyd|-nofs] -mapfile mapfile [ppmfile]

       All  options  can  be abbreviated to their shortest unique prefix.  You may use two hyphens instead of one to designate an option.  You may
       use either white space or equals signs between an option name and its value.

DESCRIPTION

       pnmquant is a newer, more general program that is backward compatible with ppmquant.  ppmquant may be faster, though.

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

       The quantization method is Heckbert's "median cut".

       Alternately, you can skip the color-choosing step by specifying your own set of colors with the -mapfile option.  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 image 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.

       If you use a mapfile, the output image has the same maxval as the mapfile.  Otherwise, the output maxval is the same as the  input  maxval,
       or less in some cases where the quantization process reduces the necessary resolution.

       The  -floyd/-fs	option	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.   How-
       ever, it does take substantially more CPU time, so the default is off.

       -nofloyd/-nofs means not to use the Floyd-Steinberg error diffusion.  This is the default.

REFERENCES

       "Color Image Quantization for Frame Buffer Display" by Paul Heckbert, SIGGRAPH '82 Proceedings, page 297.

SEE ALSO

       pnmquant(1), ppmquantall(1), pnmdepth(1), ppmdither(1), ppm(5)

AUTHOR

       Copyright (C) 1989, 1991 by Jef Poskanzer.

								  12 January 1991						       ppmquant(1)