pbmreduce

   Updated: 02 August 1989
   Table Of Contents

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.

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

   pbmreduce duplicates a lot of the functionality  of	pgmtopbm;
you could do
   something  like  pnmscale  |	 pgmtopbm, 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  de-
scription). 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  pbmre-
duce. You can
   even	 correct  the brightness of an image, by using the -value
option.

OPTIONS

   By  default,	 pbmreduce  does  the  halftoning after	 the  re-
duction 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 quan-
tizations. It
   should be a real number between 0 and 1. Above 0.5 means dark-
er images;
   below 0.5 means lighter.

SEE ALSO

   pnmenlarge, pnmscale, pgmtopbm, pbm

AUTHOR

   Copyright (C) 1988 by Jef Poskanzer.
     _________________________________________________________________



Table Of Contents

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * SEE ALSO
     * AUTHOR

UNIX/Linux commands referenced on this page:

1. as
2. pnmscale
3. pgmtopbm
4. at
5. factor
6. pnmenlarge