1. Research and Technology Group, Fuji Xerox Co. Ltd., 430 Sakai, Nakai, Kanagawa, 259-0157, Japan
2. Research and Technology Group, Fuji Xerox Co. Ltd., 6-1 Minatomirai, Nishi-ku, Yokohama, Kanagawa, 220-8668, Japan
3. Graduate School of Information Systems, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan