PPMCONVOL

NAME

      ppmconvol - general MxN convolution on a portable pixmap

SYNOPSIS

      ppmconvol <convolutionfile> [ppmfile]

DESCRIPTION

      Reads two portable pixmaps as input.  Convolves the second using the
      first, and writes a portable pixmap as output.
      Convolution means replacing each pixel with a weighted average of the
      nearby pixels.  The weights and the area to average are determined by
      the convolution matrix.  The unsigned numbers in the convolution file
      are offset by -maxval/2 to make signed numbers, and then normalized,
      so the actual values in the convolution file are only relative.
      Here is a sample convolution file; it does a simple average of the
      immediate neighbors, resulting in a smoothed image:
          P2
          3 3
          18
          10 10 10
          10 10 10
          10 10 10
      The convolution file will usually be a bitmap or graymap instead of a
      pixmap, so that the same convolution gets applied to each color
      component.  However, if you want to use a pixmap and do a different
      convolution to different colors, you can certainly do that.

SEE ALSO

      ppm(5)

AUTHOR

      Copyright (C) 1989 by Jef Poskanzer.
      Permission to use, copy, modify, and distribute this software and its
      documentation for any purpose and without fee is hereby granted,
      provided that the above copyright notice appear in all copies and that
      both that copyright notice and this permission notice appear in
      supporting documentation.  This software is provided "as is" without
      express or implied warranty.