pbmtopgm Man page

pbmtopgm General Commands Manual pbmtopgm


pbmtopgm – convert portable bitmap to portable graymap by averaging


pbmtopgm width height [pbmfile]


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 spe‐
cial 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.


netpbm(1), pgmtopbm, pbm(5)


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.

03 Sep 2001 pbmtopgm