NAME
    pbmreduce - read a portable bitmap and reduce it N times

SYNOPSIS
    pbmreduce [-floyd|-fs|-threshold ] [-value val] N [pbmfile]

DESCRIPTION
    Reads a  portable bitmap as input. Reduces it by a factor of N, and
    produces a portable bitmap as output.

    pbmreduce duplicates a lot of the functionality of pgmtopbm; you  could
    do something like pnmscale | pgmtopbm, but pbmreduce is a lot faster.

    pbmreduce can be used to "re-halftone" an image. Let's say you have a
    scanner that only produces black&white, not grayscale, and it does a
    terrible  job of halftoning (most b&w scanners fit this description).
    One way to fix the halftoning is to scan at the highest possible  reso-
    lution, say 300 dpi, and then reduce by a factor of three or so using
    pbmreduce. You can even correct the brightness of an image, by  using
    the -value flag.

OPTIONS
    By default, the halftoning after the reduction is done via boustrophe-
    donic Floyd-Steinberg error diffusion; however, the -threshold flag can
    be used to specify simple thresholding. This gives better results when
    reducing line drawings.

    The -value flag alters the thresholding value for all quantizations.
    It should be a real number between 0 and 1. Above 0.5 means darker
    images; below 0.5 means lighter.

    All flags can be abbreviated to their shortest unique prefix.

SEE ALSO
   pnmenlarge(1),pnmscale(1),pgmtopbm(1), pbm(5)

AUTHOR
    Copyright (C) 1988 by Jef Poskanzer.