pgmmedian




                                   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] [-cut-
off=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  pgm-
median 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 dimen-
sions 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, pnmaddnoise, 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

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * REFERENCES
     * SEE ALSO
     * HISTORY
     * AUTHOR


















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