I'm currently studying a Deriche filter. I've managed to create python program for derivative smoothing from this article [1]. As I understand it, Deriche used one $\alpha$ for smoothing in both directions - X and Y, so this filter seems to me isotrophic. Is it correct way to use two alphas $-$ $\alpha_x$ and $\alpha_y$ to add anistrophy?
Can someone please explain me the relaion between $\alpha$ in Deriche filter and $\sigma$ in Gaussian filter? In [1] i found an equation 2, but i do not understand the symbol П. Is it $\pi$?
Thank you.
[1]: Deriche, R. (1990). Fast algorithms for low-level vision. IEEE Transactions on Pattern Analysis and Machine Intelligence, 12(1), 78–87. doi:10.1109/34.41386