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Re: variance of pixel values

Posted by gankaku on Jan 19, 2015; 5:20pm
URL: http://imagej.273.s1.nabble.com/variance-of-pixel-values-tp5011278p5011284.html

Dear Rabih,

see attached a modified macro to measure the variance in a selection (if
there is no selection it measures the variance of the complete image).

//-----------------------
original = getTitle();
//w = getWidth();
//h = getHeight();
getStatistics(area, mean);
getSelectionBounds(x, y, width, height);

for(v=0; v<height; v++) {
for(u=0; u<width; u++) {

summedIntensitySquares = summedIntensitySquares + pow((getPixel(u,v) -
mean), 2);
}
}

variance = (1 / (width * height)) * summedIntensitySquares
RMSC = sqrt((1 / (width * height)) * summedIntensitySquares);

print("Var: " + variance);
print("SD: " + RMSC);
//----------------------------

The variance filter calculates the variance in a limited area
(neighborhood). This neighborhood will be defined by the user using the
radius since the neighborhood is created as circular form to preserve
directional isotropy.
You can convert an image under >Image >Type >...

It might be helpful for you to have a look here:
http://rsb.info.nih.gov/ij/docs/guide/146.html

Regards,
Jan

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