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Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
RedHat 6.2(Zoot) |
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pnmconvol(1) |
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pnmconvol - general MxN convolution on a portable anymap
pnmconvol convolutionfile [pnmfile]
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.
pnmsmooth(1), pnm(5)
Copyright (C)
1989, 1991 by Jef Poskanzer.
Modified 26 November 1994 by Mike Burns,
burns@chem.psu.edu
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pnmconvol(1) | |