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 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 numbers 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 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