xfree86 man page for pbmreduce

pbmreduce(1)						      General Commands Manual						      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 res-
       olution, 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.

								  02 August 1989						      pbmreduce(1)