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pgmmedian(1) |
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pgmmedian
Updated: 28 August 2005
Table Of Contents
NAME
pgmmedian - apply a median filter to a PGM file
SYNOPSIS
pgmmedian [-width=n] [-height=n] [-type=median_type] [-cutoff=int] [pnmfile]
Minimum unique abbreviation of
option is acceptable. You may use double
hyphens instead of single hyphen to denote options. You may
use white space
in place of the equals sign to separate an option name from
its value.
DESCRIPTION
This program is part of Netpbm.
pgmmedian applies a median
filter to a PGM image, using either the histogram
sort of select kth value method to determine the median.
See the -type and -cutoff
options for information on how pgmmedian chooses
between the two methods.
OPTIONS
-cutoff int
This option provides the cutoff value that pgmmedian uses to
decide
between using the histogram sort or select kth value method
to find
the median. If (maxval / ((width * height) - 1)), where
maxval is the
maxval of the image and width and height are the dimensions
of the
mask, is less than the cutoff value, pgmmedian uses
histogram sort.
Otherwise, it uses kth value.
If expression is less than the cutoff, pgmmedian uses the
histogram
sort. Otherwise it uses the select kth value method.
This option has no effect if you specify -type.
The default is 250
-width=n
Width of the median mask to apply.
Default is 3.
-height=n
Height of the median mask to apply.
Default is 3.
-type median_type
This option selects which method to use to find median
regardless of
cutoff value. Choices are histogram_sort and select.
By default, pgmmedian decides which method to use as
described under
the -cutoff option.
REFERENCES
* "Collected Algorithms
from ACM" Volume II, Algorithm 489 by Robert W.
Floyd
* "A Fast Two-Dimensional Median Filtering
Algorithm" in "IEEE
Transactions on Acoustics, Speech, and Signal
Processing" Vol. ASSP-27,
No. 1, February 1979
* "Digital Image Processing Algorithms" by Ioannis
Pitas, Prentice Hall,
1993 ISBN 0-13-145814-0
SEE ALSO
pgmnoise, pamaddnoise, pgm
HISTORY
pgmmedian was added to Netpbm in
Version 10.29 (August 2005). It had been
distributed by Mike Burns via his own web site before that
(and continued to
be so).
AUTHOR
Copyright (C) 1996 by Mike Burns
<burns@cac.psu.edu>
_________________________________________________________________
Table Of Contents
* SYNOPSIS
* DESCRIPTION
* OPTIONS
* REFERENCES
* SEE ALSO
* HISTORY
* AUTHOR
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pgmmedian(1) | |