EDGE DETECTION
Macro: -not applicable-
Function: Gradient operators: sobel and roberts, second derivative operator such as Laplacian, orthogonal templates defined by Frei-Chen for combined detection of point lines and edges, Mero-Vassy operator and the zero crossing technique to detect edges.  
Operation: '=>' implies choice of mask available for the edge operator, keep the right mouse button pressed till the mask is selected, then release the mouse button. Panels appear for image plane or parameter specification. 
