man > pgmkernel(1)

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 double hyphens instead of
       single hyphen to denote options.  You may use white space in place of the equals sign to sep‐
       arate an option name from its value.



DESCRIPTION
       This program is part of Netpbm(1).

       pgmkernel generates a convolution kernel that you can use with pnmconvol.  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 arguments.

       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 pnm‐
       convol specifies for representing the real numbers K in PGM.



OPTIONS
       In addition to the options common to all programs based on libnetpbm  (most  notably  -quiet,
       see  Common Options ), pgmkernel recognizes the following command line options:



       -weight=number
              The  distance  from  the  center  is weighted by this; a higher number 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  al‐
              ways 255.





LIMITATIONS
       The  computation  time  is proportional to width*height.  This increases rapidly with the in‐
       crease 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 AT cfa.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)