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 ), 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)