Pamgauss User Manual(1) General Commands Manual Pamgauss User Manual(1)
NAME
pamgauss - create a two-dimensional Gaussian function as a PAM image
SYNOPSIS
pamgauss width height -sigma=number [-maxval=number] [-tuple-
type=string] [-maximize] [-oversample=number]
Minimum unique abbreviation of option is acceptable. You may use dou-
ble 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 gener-
ates. Mathematically speaking, they are the domain of the two-dimen-
sional 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 nor-
mally 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 im-
age 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 ⟨index.html#commonoptions⟩ ), 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. Nor-
mally, 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 func-
tion 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 func-
tion 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 unspec-
ified tuple type.
-oversample=number
This sets the oversampling factor. pamgauss samples the Gauss-
ian 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)
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