Masao Takatoo Tadaaki Kitamura Yoshiki Kobayashi Vehicle extraction using spatial differentiation and subtraction. 21-32 1998 29 Systems and Computers in Japan 7 http://dx.doi.org/10.1002/(SICI)1520-684X(19980630)29:7<21::AID-SCJ3>3.0.CO;2-K db/journals/scjapan/scjapan29.html#TakatooKK98