sigma
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Name
sigma - noise reduction filtering
Syntax
sigma -t <t> <input> <output> [<n>]
sigma -s <s> <input> <output> [<n>]
Description
sigma filters the input image into the output
image using a sigma filter with window size n x n.
The center pixel is replaced with the average of all
pixels in the window whose value is within t
counts from the center pixel, or whose value is
within s standard deviations from the center
pixel.
The standard deviation (of the noise) is estimated
by measuring the standard deviation within every
possible n x n window, and averaging over the 10%
lowest values.
Uses histogram updating when moving horizontally
from pixel to pixel.
Default value of n is 3.
See also
sigma(3), mean(1), median(1), knn(1), kncn(1), snn(1),
minarea(1), maxarea(1), mode(1), rank(1)
Restrictions
The input image must have bands with pixel type unsigned byte.
If n is even, n is set to n+ 1.
Author
Tor Lønnestad, BLAB, Ifi, UiO.
Examples
sigma -t 20 mona.img monaSig.img 7
sigma -s 2.0 mona.img monaSig.img 7
Id
$Id: sigma.c,v 1.24 1997/01/10 16:13:47 svein Exp $