US 4674824, Goodman, Joseph W.; Hesselink, Lambertus & Ochoa, Ellen, "System for enhancement of optical features", published June 23, 1987, assigned to Stanford University
US 4838644, Ochoa, Ellen; Schils, George F. & Sweeney, Donald W., "Position, rotation, and intensity invariant recognizing method", published June 13, 1989, assigned to United States Department of Energy
US 4949389, Allebach, Jan P.; Ochoa, Ellen & Sweeney, Donald W., "Optical ranked-order filtering using threshold decomposition", published August 14, 1990, assigned to United States Department of Energy