Pgmkernel User Manual(0)			      Pgmkernel User Manual(0)



Table Contents <#index>


NAME
       pgmkernel - generate a convolution kernel


SYNOPSIS
       pgmkernel [-weight w] width  [height ]


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 size width by height (or width by
       width if you don't specify height.

       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.

       pgmkernel generates the output PGM file in the Plain  (text)  variation
       of PGM.


OPTIONS
       The  optional  -weight  value  should be a real number greater than -1.
       The default value is 6.0.


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.


SEE ALSO
       pnmconvol(1), pnmsmooth(1) pamgauss(1) pgm(1)



AUTHOR
       Alberto Accomazzi (alberto@cfa.harvard.edu).



netpbm documentation	       10 December 1992	      Pgmkernel User Manual(0)