pgmmedian(1)

1Pgmmedian User Manual(0)                              Pgmmedian User Manual(0)
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NAME

6       pgmmedian - apply a median filter to a PGM file
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SYNOPSIS

10       pgmmedian
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12       [-width=n]
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14       [-height=n]
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16       [-type=median_type]
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18       [-cutoff=int]
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20       [pnmfile]
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22       Minimum  unique abbreviation of option is acceptable.  You may use dou‐
23       ble hyphens instead of single hyphen to denote options.   You  may  use
24       white space in place of the equals sign to separate an option name from
25       its value.
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DESCRIPTION

30       This program is part of Netpbm(1).
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32       pgmmedian applies a median filter to a PGM image, using either the his‐
33       togram sort or select kth value method to determine the median.
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35       A  median  filter is a convolution filter in which the value of a pixel
36       in the output is the median of a certain set of pixels in the neighbor‐
37       hood  of  the  corresponding  input  pixel.  The effect is to eliminate
38       locally extreme values.  Such pixels typically show up as speckles.
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40       See the -type and -cutoff options  for  information  on  how  pgmmedian
41       chooses between the two methods.
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OPTIONS

46       -cutoff int
47              This  option  provides  the  cutoff value that pgmmedian uses to
48              decide between using the histogram  sort  or  select  kth  value
49              method to find the median.
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51              If (maxval / ((width * height) - 1)), where maxval is the maxval
52              of the image and width and height  are  the  dimensions  of  the
53              mask,  is  less  than the cutoff value, pgmmedian uses histogram
54              sort.  Otherwise, it uses kth value.
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56              This option has no effect if you specify -type.
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58              The default is 250
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61       -width=n
62              Width of the median mask to apply.
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64              Default is 3.
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67       -height=n
68              Height of the median mask to apply.
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70              Default is 3.
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73       -type median_type
74              This option selects which method to use to find  median  regard‐
75              less of cutoff value.  Choices are histogram_sort and select.
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77              By  default,  pgmmedian decides which method to use as described
78              under the -cutoff option.
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REFERENCES

84       ·      "Collected Algorithms from ACM"  Volume  II,  Algorithm  489  by
85              Robert W. Floyd
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88       ·      "A  Fast  Two-Dimensional  Median  Filtering Algorithm" in "IEEE
89              Transactions on Acoustics, Speech, and Signal  Processing"  Vol.
90              ASSP-27, No. 1, February 1979
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93       ·      "Digital Image Processing Algorithms" by Ioannis Pitas, Prentice
94              Hall, 1993 ISBN 0-13-145814-0
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HISTORY

105       pgmmedian was added to Netpbm in Version 10.29 (August 2005).   It  had
106       been  distributed  by  Mike Burns via his own web site before that (and
107       continued to be so).
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AUTHOR

112       Copyright (C) 1996 by Mike Burns <burns@cac.psu.edu>
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DOCUMENT SOURCE

115       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
116       source.  The master documentation is at
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118              http://netpbm.sourceforge.net/doc/pgmmedian.html
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120netpbm documentation            28 August 2005        Pgmmedian User Manual(0)