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1995-01-23
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pnmconvol(1) AMIGA (26 November 1994) pnmconvol(1)
NAME
pnmconvol - general MxN convolution on a portable anymap
SYNOPSIS
pnmconvol convolutionfile [pnmfile]
DESCRIPTION
Reads two portable anymaps as input. Convolves the second
using the first, and writes a portable anymap 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 nine immediate neighbors, resulting in a smoothed
image:
P2
3 3
18
10 10 10
10 10 10
10 10 10
To see how this works, do the above-mentioned offset: 10 -
18/2 gives 1. The possible range of values is from 0 to 18,
and after the offset that's -9 to 9. The normalization step
makes the range -1 to 1, and the values get scaled
correspondingly so they become 1/9 - exactly what you want.
The equivalent matrix for 5x5 smoothing would have maxval 50
and be filled with 26.
The convolution file will usually be a graymap, 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
pnmsmooth(1), pnm(5)
AUTHORS
Copyright (C) 1989, 1991 by Jef Poskanzer.
Modified 26 November 1994 by Mike Burns, burns@chem.psu.edu
Page 1 (printed 1/23/95)