An averaging edge detector

Abstract

The problem of improving the accuracy of edge angle measurements using a hardware Sobel edge detector and a three pixel square convolver has been considered. Better edge angle estimates can be obtained by averaging the output of the Sobel masks over a 3×3 window. The exclusion of the contribution of the central pixel of the window gives the best performance from the point of view of both angle measurement bias and resilience to noise. The superior performance of the above averaging strategy has been explained with the help of the equivalent 5 × 5 mask which would yield identical results in one pass through the image. It is further shown that an additional improvement in the edge angle measurement can be obtained by prefiltering the image using a 5 × 5 median filter. © 1987.