1. Océ-Technologies B.V. P.O. Box 101, 5900 MA Venlo The Netherlands
2. University of Twente Department of Electrical Engineering P.O. Box 217, 7500 AE Enschede The Netherlands
3. ATO-DLO P.O. Box 17, 6700 AA Wageningen The Netherlands
4. Free University Amsterdam Computer Science Department De Boelelaan 1081a, 1081 HV Amsterdam The Netherlands