ppmquant(1)          AMIGA (12 January 1991)          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] -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 "median cut".

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

     SEE ALSO
          ppmquantall(1), pnmdepth(1), ppmdither(1), ppm(5)



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     ppmquant(1)          AMIGA (12 January 1991)          ppmquant(1)



     AUTHOR
          Copyright (C) 1989, 1991 by Jef Poskanzer.





















































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