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

You can abbreviate any option to its shortest unique prefix.

This program is part of Netpbm.

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

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 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 option.

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 bet-
ter 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.

pamenlarge, pamscale, pamditherbw, pbm

Copyright (C) 1988 by Jef Poskanzer.

netpbm documentation 02 August 1989 Pbmreduce User Manual(0)