Manual: pgmkernel

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 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 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 be‐
       yond 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 rep‐
       resenting 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 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 nonnegative 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)