convert portable bitmap to portable graymap by averaging
width height [pbmfile]
reads a portable bitmap as input. It outputs a portable
graymap in which each pixel’s gray level is the
average the surrounding black and white input pixels. The
surrounding area is a rectangle of width by
In other words,
this is a convolution. pbmtopgm is similar to a
special case of pnmconvol.
You may need a
ppmsmooth step after pbmtopgm.
has the effect of anti-aliasing bitmaps which contain
distinct line features.
works best with odd sample width and heights.
need pbmtopgm just to use a PGM program on a PBM
image. Any PGM program (assuming it uses the Netpbm
libraries to read the PGM input) takes PBM input as if it
were PGM, with only the mininum and maximum gray levels. So
unless your convolution rectangle is bigger than one pixel,
you’re not gaining anything with a pbmtopgm
1990 by Angus Duggan Copyright (C) 1989 by Jef
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