Trung Thanh Nguyen Claire P. Willis Derek J. Paddon Sinh Hoa Nguyen Hung Son Nguyen Learning Sunspot Classification. 295-309 2006 72 Fundam. Inform. 1-3 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=72&issue=1&spage=295 db/journals/fuin/fuin72.html#NguyenWPNN06