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 lo‐
38       cally extreme values.  Such pixels typically show up as speckles.
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40       Pixels at the edges of the image, pixels where the  convolution  kernel
41       would  go  off the edge of the image, are just copied.  For example, if
42       -height is 9, the first 4 and last 4 rows of the input image  are  just
43       copied to the output.
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46       See  the  -type  and  -cutoff  options for information on how pgmmedian
47       chooses between the two methods.
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OPTIONS

52       In addition to the options common to all programs  based  on  libnetpbm
53       (most notably -quiet, see
54        Common  Options ⟨index.html#commonoptions⟩ ), pgmmedian recognizes the
55       following command line options:
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59       -cutoff int
60              This option provides the cutoff value that pgmmedian uses to de‐
61              cide between using the histogram sort or select kth value method
62              to find the median.
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64              If (maxval / ((width * height) - 1)), where maxval is the maxval
65              of  the  image  and  width  and height are the dimensions of the
66              mask, is less than the cutoff value,  pgmmedian  uses  histogram
67              sort.  Otherwise, it uses kth value.
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69              This option has no effect if you specify -type.
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71              The default is 250
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74       -width=n
75              Width of the median mask to apply.
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77              Maximum allowed is the width of the input image.
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79              Default is 3.
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82       -height=n
83              Height of the median mask to apply.
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85              Maximum allowed is the height of the input image.
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87              Default is 3.
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90       -type median_type
91              This  option  selects which method to use to find median regard‐
92              less of cutoff value.  Choices are histogram_sort and select.
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94              By default, pgmmedian decides which method to use  as  described
95              under the -cutoff option.
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REFERENCES

101       •      "Collected  Algorithms  from  ACM"  Volume  II, Algorithm 489 by
102              Robert W. Floyd
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105       •      "A Fast Two-Dimensional Median  Filtering  Algorithm"  in  "IEEE
106              Transactions  on  Acoustics, Speech, and Signal Processing" Vol.
107              ASSP-27, No. 1, February 1979
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110       •      "Digital Image Processing Algorithms" by Ioannis Pitas, Prentice
111              Hall, 1993 ISBN 0-13-145814-0
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HISTORY

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

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

132       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
133       source.  The master documentation is at
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135              http://netpbm.sourceforge.net/doc/pgmmedian.html
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137netpbm documentation            20 January 2022       Pgmmedian User Manual(0)