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Pbmreduce User Manual
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pbmreduce
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Updated: 02 August 1989
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Table Of Contents
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NAME
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pbmreduce - read a PBM image and reduce it N times
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SYNOPSIS
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\fBpbmreduce\fR
[\fB-floyd\fR|\fB-fs\fR|\fB-threshold\fR]
[\fB-value\fR \fIval\fR]
\fIN\fR
[\fIpbmfile\fR]
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You can abbreviate any option to its shortest unique prefix.
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DESCRIPTION
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This program is part of Netpbm.
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\fBpbmreduce\fR reads a PBM image as input and reduces it by a
factor of \fIN\fR, producing a PBM image as output.
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\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.
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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.
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OPTIONS
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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.
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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.
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SEE ALSO
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pamenlarge,
pamscale,
pamditherbw,
pbm
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AUTHOR
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Copyright (C) 1988 by Jef Poskanzer.
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Table Of Contents
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