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.TL
Pbmreduce User Manual
.SH 1
pbmreduce
.LP
Updated: 02 August 1989
.br
Table Of Contents
.SH 2
NAME
.LP
pbmreduce - read a PBM image and reduce it N times
.SH 2
SYNOPSIS
.LP
\fBpbmreduce\fR
[\fB-floyd\fR|\fB-fs\fR|\fB-threshold\fR]
[\fB-value\fR \fIval\fR]
\fIN\fR
[\fIpbmfile\fR]
.LP
You can abbreviate any option to its shortest unique prefix.
.SH 2
DESCRIPTION
.LP
.LP
This program is part of Netpbm.
.LP
\fBpbmreduce\fR reads a PBM image as input and reduces it by a
factor of \fIN\fR, producing a PBM image as output.
.LP
\fBpbmreduce\fR duplicates a lot of the functionality of
\fBpamditherbw\fR; you could do something like \f(CWpamscale |
pamditherbw\fR, but \fBpbmreduce\fR is a lot faster.
.LP
You can use \fBpbmreduce\fR 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 \fBpbmreduce\fR.  You can even
correct the brightness of an image, by using the \fB-value\fR option.
.SH 2
OPTIONS
.LP
.LP
By default, \fBpbmreduce\fR does the halftoning after the
reduction via boustrophedonic Floyd-Steinberg error diffusion;
however, you can use the \fB-threshold\fR option to specify simple
thresholding.  This gives better results when reducing line drawings.
.LP
The \fB-value\fR 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.
.SH 2
SEE ALSO
.LP
pamenlarge,
pamscale,
pamditherbw,
pbm
.SH 2
AUTHOR
.LP
Copyright (C) 1988 by Jef Poskanzer.
.br
\l'5i'
.SH 2
Table Of Contents
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AUTHOR
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