Edge detection method based on edge reliability with fixed thresholds: consideration of uniformity and gradation

This paper proposes a robust method of detecting edge points by thresholding edge reliability with fixed threshold values. Traditionally edge detection is done by thresholding edge height. One crucial problem is that the threshold is determined ad hoc for the given input image. We use edge reliability instead of edge height, and show that two fixed thresholds work well. In our previous paper (1996) we proposed an edge vector extractor and stated the necessity of a measure, edge reliability, which can discriminate a low but steady edge from a noisy edge of large edge height. Our idea of extracting edge points is to detect points which are neither in a uniform region nor in a gradational region. The two detection thresholds, √2/π and √3/4, are derived from the analysis of edge reliability in uniform regions and gradational regions contaminated by white Gaussian noises, respectively. Experiments show that our method can detect edge points stably, discriminating them from the points in uniform or gradational regions influenced by noises