public static interface AnisotropicDiffusion.DiffusionFunction
The interface that function suitable to be diffusion function must implement.
It is very simple and has some limitation: in Perona & Malik scheme, the gradient
at each arc location is approximated by the absolute value of its projection along the
direction of the arc (see paper, p. 633). Functions implementing this interface are
therefore provided only with a single component of the gradient, and must return the
diffusion contribution in that direction.