Pgmkernel User Manual(1) General Commands Manual Pgmkernel User Manual(1)
NAME
pgmkernel - generate a convolution kernel
SYNOPSIS
pgmkernel [-weight=number] [-maxval=] {size | width height}
Minimum unique abbreviation of option is acceptable. You may use dou-
ble 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).
pgmkernel generates a convolution kernel that you can use with pnmcon-
vol. The kernel is one where the weight of each location is inversely
proportional to its distance from the center of the kernel.
pgmkernel generates a PGM image of width and height size if you specify
one argument, or width width and height height if you specify two argu-
ments.
pgmkernel computes the convolution function K as follows.
K(i,j) = 1 / ( 1 + w * sqrt(i^2 + j^2))
where w is a coefficient specified via the -weight option. i and j are
measured in pixels. K is zero everywhere beyond the specified kernel
width and height.
The sample values in the PGM output have this value scaled and biased
using the protocol pnmconvol specifies for representing the real num-
bers K in PGM.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pgmkernel recognizes the
following command line options:
-weight=number
The distance from the center is weighted by this; a higher num-
ber means the value falls off more quickly as you go away from
the center.
This must be a positive real number.
The default is 6.0.
-maxval=maxval
The maxval for the PGM kernel.
Default is 255.
This option was new in Netpbm 10.65 (December 2013). Before
that, the maxval is always 255.
LIMITATIONS
The computation time is proportional to width*height. This increases
rapidly with the increase of the kernel size. A better approach could
be using a FFT in these cases.
HISTORY
Before Netpbm 10.65 (December 2013), the output was always in Plain
(text) PGM format. (Now, like standard Netpbm programs, the default is
raw PGM and you can get Plain PGM with a -plain option).
Before Netpbm 10.65 (December 2013), this manual said negative values
for -weight were valid (as long as they were greater than -1.0). But
the program never worked with negative numbers and it isn't clear that
the result would be useful, so -weight is now required to be nonnega-
tive and the program fails gracefully if you specify a negative value.
SEE ALSO
pnmconvol(1), pnmsmooth(1) pamgauss(1) pgm(1)
AUTHOR
Alberto Accomazzi (alberto@cfa.harvard.edu).
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/pgmkernel.html
netpbm documentation 19 December 2013 Pgmkernel User Manual(1)
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