pbmreduce(1)             UNIX System V(02 August 1989)             pbmreduce(1)


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 resolution,
      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
      boustrophedonic 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.
















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