\
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.TH "Pbmreduce User Manual" 0 "02 August 1989" "netpbm documentation"

.SH NAME

pbmreduce - read a PBM image and reduce it N times

.UN synopsis
.SH SYNOPSIS

\fBpbmreduce\fP
[\fB-floyd\fP|\fB-fs\fP|\fB-threshold\fP]
[\fB-value\fP \fIval\fP] \fIN\fP
[\fIpbmfile\fP]
.PP
You can abbreviate any option to its shortest unique prefix.

.UN description
.SH DESCRIPTION
.PP
This program is part of
.BR Netpbm (1)
.
.PP
\fBpbmreduce\fP reads a PBM image as input and reduces it by a
factor of \fIN\fP, producing a PBM image as output.
.PP
\fBpbmreduce\fP duplicates a lot of the functionality of
\fBpamditherbw\fP; you could do something like \f(CWpamscale |
pamditherbw\fP, but \fBpbmreduce\fP is a lot faster.
.PP
You can use \fBpbmreduce\fP 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\fP.  You can even
correct the brightness of an image, by using the \fB-value\fP option.

.UN options
.SH OPTIONS
.PP
By default, \fBpbmreduce\fP does the halftoning after the
reduction via boustrophedonic Floyd-Steinberg error diffusion;
however, you can use the \fB-threshold\fP option to specify simple
thresholding.  This gives better results when reducing line drawings.
.PP
The \fB-value\fP 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.

.UN seealso
.SH SEE ALSO
.BR pamenlarge (1)
,
.BR pamscale (1)
,
.BR pamditherbw (1)
,
.BR pbm (5)


.UN author
.SH AUTHOR

Copyright (C) 1988 by Jef Poskanzer.