[1] Chinese Univ Hong Kong, Dept Informat Engn, Shatin, Hong Kong, Peoples R China
[2] Chinese Acad Sci, Inst Automat, Natl Pattern Recognit Lab, Beijing 100080, Peoples R China
[3] Avaya Labs Res, Basking Ridge, NJ 07920 USA
[4] Univ Genoa, Dept Commun Comp & Syst Sci, Comp Vis Lab, I-16126 Genoa, Italy