A method of designing filters for filtering digitized images includes constructing a set of difference-of-Gaussian (DoG) filters that partition a frequency space, forming a linear combination of said DoG filters to form a trial filter, convolving said trial filter with a training image to obtain a trial image, summing a square difference of said trial image and a target image, wherein if said sum is a minimum, outputting said trial filter as a final filter, and using a singular value decomposition on said final filter wherein an eigenvector corresponding to the largest eigenvalue of the final filter is obtained.