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Alex Schuster wrote:

> For some 3x3 pixels x_i (and a mean of x_mean), the standard deviation
> is
> s = 1/9 * sqrt( sum( (x_i-x_mean)^2 ) ). img=img-smooth(img,3) does the
> inner subtraction of the x_means,

unfortunately, that's not quite true (except for special cases) since the x_i
get only their respective mean subtracted, not the center pixel mean. I came
up with the same solution initially but it would not stand the test ...

haven't had a better idea since :(

Benno Puetz
Max-Planck-Institut f. Psychiatrie            Tel.: +49-89-30622-413
Kraepelinstr. 10                              Fax : +49-89-30622-520
80804 Muenchen, Germany