pgmkernel(1)

1Pgmkernel User Manual(0)                              Pgmkernel User Manual(0)
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NAME

9       pgmkernel - generate a convolution kernel
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SYNOPSIS

13       pgmkernel [-weight=number] [-maxval=] {size | width height}
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15       Minimum  unique abbreviation of option is acceptable.  You may use dou‐
16       ble hyphens instead of single hyphen to denote options.   You  may  use
17       white space in place of the equals sign to separate an option name from
18       its value.
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DESCRIPTION

23       This program is part of Netpbm(1).
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25       pgmkernel generates a convolution kernel that you can use with  pnmcon‐
26       vol.   The kernel is one where the weight of each location is inversely
27       proportional to its distance from the center of the kernel.
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29       pgmkernel generates a PGM image of width and height size if you specify
30       one argument, or width width and height height if you specify two argu‐
31       ments.
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33       pgmkernel computes the convolution function K as follows.
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35              K(i,j) = 1 / ( 1 + w * sqrt(i^2 + j^2))
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37       where w is a coefficient specified via the -weight option.  i and j are
38       measured  in  pixels.  K is zero everywhere beyond the specified kernel
39       width and height.
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41       The sample values in the PGM output have this value scaled  and  biased
42       using  the  protocol pnmconvol specifies for representing the real num‐
43       bers K in PGM.
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OPTIONS

48       -weight=number
49              The distance from the center is weighted by this; a higher  num‐
50              ber  means  the value falls off more quickly as you go away from
51              the center.
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53              This must be a positive real number.
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55              The default is 6.0.
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58       -maxval=maxval
59              The maxval for the PGM kernel.
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61              Default is 255.
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63              This option was new in Netpbm  10.65  (December  2013).   Before
64              that, the maxval is always 255.
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LIMITATIONS

71       The  computation  time is proportional to width*height.  This increases
72       rapidly with the increase of the kernel size.  A better approach  could
73       be using a FFT in these cases.
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HISTORY

77       Before  Netpbm  10.65  (December  2013), the output was always in Plain
78       (text) PGM format.  (Now, like standard Netpbm programs, the default is
79       raw PGM and you can get Plain PGM with a -plain option).
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81       Before  Netpbm  10.65 (December 2013), this manual said negative values
82       for -weight were valid (as long as they were greater than  -1.0).   But
83       the  program never worked with negative numbers and it isn't clear that
84       the result would be useful, so -weight is now required to  be  nonnega‐
85       tive and the program fails gracefully if you specify a negative value.
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AUTHOR

94       Alberto Accomazzi (alberto@cfa.harvard.edu).
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DOCUMENT SOURCE

97       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
98       source.  The master documentation is at
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100              http://netpbm.sourceforge.net/doc/pgmkernel.html
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102netpbm documentation           19 December 2013       Pgmkernel User Manual(0)