I saw an imaging program some time ago on an Amiga that had
Cross, Sobel and Roberts filters for edge detection. 

Can anybody direct me to these algorithms.

Paul Denize

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Paul Denize                                Internet: PDenize@Waikato.ac.nz
Department of Computer Science
University of Waikato                         phone: ++64 7 8562-889
Hamilton                                                          Ext 8743
NEW ZEALAND                                   fax  : ++64 7 8560-135