Optimal linear filters for preliminary processing of images

Heuristic methods of-prel iminary image processing used some position-invariant operators [ I ] [ 3 ] . This term was used to denote operators on images, which are permutable with any image-transfer operation in the field of view. Thus, in order to isolate a contour one makes use either of a discrete analog of the Laplace operator or of the gradient modulus; for smoothing purposes one uses the operator consisting of averaging over a vicinity.