Pbmtopgm User Manual(0) Pbmtopgm User Manual(0)NAMEpbmtopgm - convert PBM image to PGM by averaging areas
SYNOPSISpbmtopgm width height [pbmfile]
DESCRIPTION
This program is part of Netpbm(1).
pbmtopgm reads a PBM image as input. It outputs a PGM image in which
each pixel's gray level is the average of the surrounding black and
white input pixels. The surrounding area is a rectangle of width by
height pixels.
In other words, this is a convolution. pbmtopgm is similar to a spe‐
cial case of pnmconvol.
You may need a pnmsmooth step after pbmtopgm.
pbmtopgm has the effect of anti-aliasing bitmaps which contain distinct
line features.
pbmtopgm works best with odd sample width and heights.
You don't 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 step.
The opposite transformation (which would turn a PGM into a PBM) is
dithering. See pamditherbw.
SEE ALSOpamditherbw(1), pnmconvol(1), pbm(1), pgm(1)AUTHOR
Copyright (C) 1990 by Angus Duggan.
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, pro‐
vided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in sup‐
porting documentation. This software is provided 'as is' without
express or implied warranty.
netpbm documentation 05 Feb 2003 Pbmtopgm User Manual(0)
