NAME

       pamgauss - create a two-dimensional Gaussian function as a PAM image

SYNOPSIS

       pamgauss width height -sigma=number [-maxval=number] [-tupletype=string] [-maximize] [-oversample=number]

       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.

EXAMPLES

            pamgauss 7 7 -sigma=.5 -maximize -tupletype=GRAYSCALE | pamtopnm >gauss.pgm
            pnmconvol -nooffset -normalize gauss.pgm myimage.ppm >blurred.ppm

DESCRIPTION

       This program is part of Netpbm(1).

       pamgauss generates a one-plane PAM image whose samples are a Gaussian function of their distance from the
       center of the image.  I.e.  the sample value is highest in the center and goes  down,  in  a  bell  curve
       shape, as you move away from the center.

       You can use this image as a convolution kernel with pnmconvol to blur an image.  (This technique is known
       as Gaussian blurring).

       width  and height are the dimensions of the image that pamgauss generates.  Mathematically speaking, they
       are the domain of the two-dimensional Gaussian function.  If you want to be sure you get a whole Gaussian
       function, make sure that you choose a standard deviation and image dimensions so that if you made it  any
       larger, the sample values at the edges would be zero.

       The output image is PAM.  To make it usable with pnmconvol, specify -tupletype=GRAYSCALE so pnmconvol can
       use  it as if it were PGM.  You must use the -nooffset option on pnmconvol because zero means zero in the
       PAM that pamgauss generates.

       Without -maximize, the sum of all the samples is equal to the image's  maxval  (within  rounding  error).
       This  is  true  even  if  you  clip the Gaussian function by making the image too small.  This is what is
       normally required of a convolution kernel.

       pamgauss oversamples and averages to represent the continuous Gaussian function in  discrete  samples  in
       the  PAM output.  Consider an image 11 samples wide and an oversampling factor of 10.  The samples can be
       thought of as contiguous squares one unit wide.  The center of the image is thus the center  of  the  6th
       sample  from  the  left.  The 3rd sample from the left covers a range of distances from 3 to 4 units from
       the center of the image.  Because the oversampling factor is 10,  pamgauss  computes  the  value  of  the
       Gaussian  function  at  10  points  evenly  spaced between 3 and 4 units from the center of the image and
       assigns the 3rd sample from the left the mean of those 10 values.

OPTIONS

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

       -sigma=number
              This  is  the standard deviation of the Gaussian function.  The higher the number, the more spread
              out the function is.  Normally, you want to make this number low enough that the function  reaches
              zero value before the edge of your image.

              number is in units of samples.

              This option is required.  There is no default.

       -maximize
              Causes  pamgauss  to  use the whole dynamic range available in the output PAM image by choosing an
              amplitude for the Gaussian function that causes the maximum value in the image to be the maxval of
              the image.

              If you select this, you probably want to normalize the output  (scale  the  samples  down  so  the
              volume  under  the  surface of the two-dimensional Gaussian function is the maxval) before you use
              it, for example with pnmconvol's -normalize option.  The reason this is different  from  just  not
              using  -maximize  is  that this subsequent normalization can be done with much more precision than
              can be represented in a PAM image.

              Without this option, pamgauss uses an amplitude that makes the volume under  the  surface  of  the
              two-dimensional  Gaussian  function  the  maxval  of the image.  This means all the samples in the
              image are normally considerably less than the maxval.

              This option was new in Netpbm 10.79 (June 2017).

       -maxval=number
              This is the maxval for the output image.  65535 is almost always the best value to use.  But there
              may be some programs (not part of Netpbm) that can't handle a maxval greater than 255.

              The default is 255.

       -tupletype=string
              This is the value of the "tuple_type" attribute of the created PAM image.  It can be any string up
              to 255 characters.

              If you don't specify this, pamgauss generates a PAM with unspecified tuple type.

       -oversample=number
              This sets the oversampling factor.  pamgauss samples the Gaussian function this many  times,  both
              horizontally and vertically, to get the value of each sample in the output.

              An  oversampling  factor  of 1 means no oversampling, which means each sample is based only on the
              value of the Gaussian function at the center of the sample.

              The default is 5 divided by the standard deviation, rounded up to a whole number.

              This option was new in Netpbm 10.79 (June 2017).  Before that, it is essentially 1 - there  is  no
              oversampling.

SEE ALSO

       pnmconvol(1), pamtopnm(1), pgmkernel(1), pamseq(1), pam(1)

HISTORY

       pamgauss was new in Netpbm 10.23 (July 2004).

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/pamgauss.html

netpbm documentation                               18 May 2017                           Pamgauss User Manual(1)