Complex-Valued Feature Masks by Directional Filtering of 3×3 Compass Feature Masks

Abstract

: A two-dimensional (2D) N-directional edge detection filter was represented as a pair of real masks, i.e. by one complex-valued matrix [1]. The 3 × 3 compass gradient edge masks have often been used because of their simplicity, where N compass masks are constructed by rotating the kernel mask by an incremental angle of 2ź/N. This paper presents complex-valued feature masks formulated by directional filtering of 3 × 3 feature masks (e.g. Prewitt, Sobel, Frei-Chen, Kirsch and roof masks), with the different number of directions N (= 8, 4 and 2). The same concept can be applied to any types of filtering/masks with arbitrary N.