Walsh descriptors for polygonal curves

Abstract

Shape discrimination using boundary information is well established and a number of methods are available to extract features from the boundary trace. In this paper a boundary scalar transform technique, wherein the pattern boundary is expressed in finite Walsh series expansion, is presented for the description and discrimination of polygonal curves. As the Walsh sequency spectra are not invariant to cyclic shift of the starting point on the boundary, two preprocessing methods have been suggested to normalize the starting point. A method is also presented for the reconstruction of the pattern boundary using Walsh descriptors. Finally, computer simulation results of experiments conducted to test the discriminatory power of Walsh descriptors and the effectiveness of the normalization of the starting point are presented and discussed.