NAME¶
pbmtopgm - convert portable bitmap to portable graymap by averaging areas
SYNOPSIS¶
pbmtopgm width height [
pbmfile]
DESCRIPTION¶
pbmtopgm 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
height pixels.
In other words, this is a convolution.
pbmtopgm is similar to a special
case of
pnmconvol.
You may need a
ppmsmooth 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.
SEE ALSO¶
netpbm(1),
pgmtopbm(1),
pbm(5)
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, 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.