Complex-valued feature masks by directional filtering of 3 x 3 compass feature masks
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 x 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 2pi/N. This paper presents complex-valued feature masks formulated by directional filtering of 3x3 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.
directional filtering edge detection compass gradient edge mask discrete fourier transform discrete hartley transform