In the paper a comparative study of two methods, based on the second order Taylor series, is presented. The 3x3 pixel block modelling is performed with the derived convolution filters. It has been shown, that the 3-D edge detection with Hessian eigenvalues ratio, as suggested in the SIFT algorithm, depends strongly on the computation technique, and therefore an alternative method, also based on the Hessian eigenvalues, has been derived. The study is illustrated with the computational examples.
