1. Picture Processing by Computer;Rosenfeld,1969
2. G. Szego, Orthogonal Polynomials, American Mathematical Society, Providence, Rhode Island.
3. An operator which locates edges in digitized pictures;Hueckel;J. Assoc. Comput. Mach.,1971
4. A local visual operator which recognizes edges and lines;Hueckel;J. Assoc. Comput. Mach.,1973
5. Finding picture edges through collinearity of feature points;Gorman,1973