GradientType → Automatic
computes the gradient using the formula
is a directional derivative. Typically, n=2 and the derivatives are taken along the rows and columns of the image (PrewittFilter
). In the case of the Frei-Chen edge operator, n=4.
GradientType → None
returns a list of directional derivative images resulting from the application of each of the edge operators to the image img
The option NonMaxSuppress→True
permits the elimination (i.e., suppression) of edge responses that are not locally maximum. In effect this causes the thinning of the edges in the gradient image by suppressing gradient values with larger neighbors in the direction of the gradient.