“…1. edge detectors based on cellular NNs [36], [37], [38], [39], [40], [41], [42], [43]; 2. edge detectors based on self-organizing maps [44], [45], [46]; 3. edge detectors based on Hopfield networks [47], [48], [49], [50]; 4. edge detectors based on multilayer NNs [51], [52], [53], [54]. The above edge detectors, except class 4, are unsupervised ones and, thus, they do not have the function of enhancing the desired edges.…”