imnoise does not work as expected
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imnoise(a, 'gaussian', mean, var) seems simple enough in concept: add a Gaussian distribution of noise to an image. However, it does not recover the values expected.
Try: >> a = zeros(16, 16); b = imnoise(a, 'gaussian', 0, 0.1); >> mean(b(:)) ans = 0.1262 >> std(b(:))^2 ans = 0.040
The mean is not zero! The variance is not 0.1!
I can't figure out why the imnoise code produces this result. The code snippet is below.
switch code case 'gaussian' % Gaussian white noise b = a + sqrt(p4)*randn(sizeA) + p3;
If a = 0 and p3 = 0, then the result should have a mean value of zero.