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SIGMA

Section: C Library Functions (3)
Updated: 16 Mar 1998
Index

NAME

sigma, sigmat, noiseStDev - noise reduction filtering

SYNTAX

void sigma( IBAND input, IBAND output, int n,
float s );
void sigmat( IBAND input, IBAND output, int n,
int t );
float noiseStDev( IBAND input, int n );

DESCRIPTION

sigmafilters the inputband into the outputband using a sigma filter with window size nx n.The center pixel is replaced with the average of allpixels in the window whose value is within sstandard deviations from the center pixel. The implementationcalls noiseStDevto obtain an estimate of the noisestandard deviation, multiplies with sto obtain theparameter t,and finally calls sigmat.

sigmatfilters the input band into the outputband using a sigma filter with window size nx n.The center pixel is replaced with the average of allpixels in the window whose value is within tcountsfrom the center pixel. Uses histogram updating whenmoving horizontally from pixel to pixel.

noiseStDevestimates the noise standard deviationby measuring the standard deviation within everypossible nx nwindow, and averaging over the10% lowest values. Returns the standard deviation.

RESTRICTIONS

inputand outputmust both have pixel type unsigned byte.

RETURN VALUE

For sigmat

0 : OK
1 : Bad input pixel type
2 : Bad output pixel type

For noiseStDev

-1 : Bad input pixel type
>= 0 : Standard deviation

For sigma

0 : Ok
1 : Bad input pixel type
>1 : Error in sigmat

AUTHOR

Tor Lřnnestad, BLAB, Ifi, UiO

ID

$Id: sigma.c,v 1.24 1997/01/10 16:13:47 svein Exp $

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