Comments on ``digital step edges from zero crossings of second directional derivatives''.

In a recent paper,1 Haralick published an edge detection scheme that was supported, in part, by an evaluation against the Prewitt and the Marr-Hildreth (¿2G) operators. This evaluation led to the conclusion that Haralick's method performed the best, and the ¿2G operator performed the worst. The implementation of the ¿2G operator, on which this evaluation was based, differed significantly from that used by Marr and Hildreth. Evaluation of the performance of the Marr-Hildreth implementation of the ¿2G operator on similar images shows that this edge detection method in fact performs comparably to the Prewitt and Haralick operators.