DynamicPSF - Question about the documentation

[rcolombari]

Hi Everyone!
I was reading the DynamicPSF documentation and I got stuck at this point:

" Sigmax, Sigmay — Standard deviation of the Gaussian distribution on the horizontal and vertical axes, measured in pixels. "

I was wondering how could these sigmas be in pixels. Isn't sigma something like this: Sqrt(Sum((PixelValue(xi, yj) - mean)^2/TotalPixels))

Thanks.
Cheers!

Roberto