Toshiyuki Sakai Makoto Nagao Hitoshi Matsushima Extraction of invariant picture sub-structures by computer. 81-96 1972 1 Comput. Graph. Image Process. 1 https://doi.org/10.1016/S0146-664X(72)80008-X db/journals/cvgip/cvgip1.html#SakaiNM72