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Pgmmedian User Manual(0)						 Pgmmedian User Manual(0)

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(1)

       pgmmedian  applies  a  median  filter  to  a PGM image, using either the histogram sort or
       select kth value method to determine the median.

       A median filter is a convolution filter in which the value of a pixel in the output is the
       median  of  a  certain set of pixels in the neighborhood of the corresponding input pixel.
       The effect is to eliminate locally extreme values.   Such  pixels  typically  show  up  as
       speckles.

       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.

	      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
       o      'Collected Algorithms from ACM' Volume II, Algorithm 489 by Robert W. Floyd

       o      'A Fast Two-Dimensional Median Filtering Algorithm' in 'IEEE Transactions on Acous-
	      tics, Speech, and Signal Processing' Vol. ASSP-27, No. 1, February 1979

       o      'Digital Image Processing Algorithms' by Ioannis Pitas, Prentice	Hall,  1993  ISBN
	      0-13-145814-0

SEE ALSO
       pgmnoise(1) , pamaddnoise(1) , pnmconvol(1) , pgmmorphconv(1) , pgm(1)

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>

netpbm documentation			  28 August 2005		 Pgmmedian User Manual(0)
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