NAME
    pbmtopgm - convert PBM image to PGM 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 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.

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, 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.