Pbmreduce User Manual(0)                              Pbmreduce User Manual(0)



NAME
       pbmreduce - read a PBM image and reduce it N times


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

       You can abbreviate any option to its shortest unique prefix.


DESCRIPTION
       This program is part of Netpbm(1)

       pbmreduce reads a PBM image as input and reduces it by a factor of N,
       producing a PBM image as output.

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

       You can use pbmreduce 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 option.


OPTIONS
       By default, pbmreduce does the halftoning after the reduction via
       boustrophedonic Floyd-Steinberg error diffusion; however, you can use
       the -threshold option to specify simple thresholding.  This gives
       better results when reducing line drawings.

       The -value option 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.


SEE ALSO
       pamenlarge(1) , pamscale(1) , pamditherbw(1) , pbm(5)



AUTHOR
       Copyright (C) 1988 by Jef Poskanzer.

netpbm documentation            02 August 1989        Pbmreduce User Manual(0)