Pbmreduce User Manual(0) Pbmreduce User Manual(0)
pbmreduce - read a PBM image and reduce it N times
pbmreduce [-floyd|-fs|-threshold] [-value val] N [pbmfile]
You can abbreviate any option to its shortest unique prefix.
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
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 bous-
trophedonic 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.
pnmenlarge(1), pamscale(1), pamditherbw(1), pbm(1)
Copyright (C) 1988 by Jef Poskanzer.
netpbm documentation 02 August 1989 Pbmreduce User Manual(0)
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