Variance using median filter

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Albert Tagtum
Albert Tagtum on 20 Jun 2022
Edited: DGM on 21 Jun 2022
Hi,
In calculating variance using definition and implementing median filter why does in the code
variance = medfilt2(double(I_noise).^2, [N N], 'symmetric') - (medfilt2(double(I_noise), [N N],'symmetric')).^2;
produce zero in all points of an image?
How do I correctly calculate the variance of a median filtered image?

Answers (1)

Jon
Jon on 20 Jun 2022
In your expression:
variance = medfilt2(double(I_noise).^2, [N N], 'symmetric') - (medfilt2(double(I_noise), [N N],'symmetric')).^2;
both of the terms on the right hand side of the expression are identical. Subtracting one from the other will obviously give zero.
This is the same for example as the expression:
x = 2 - 2
which of course gives an answer of x = 0;
Also I think you are getting confused about median and average.

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