Yuan Li Haizhou Ai Chang Huang Shihong Lao Robust Head Tracking Based on a Multi-State Particle Filter. 335-340 2006 conf/fgr/2006 FG http://doi.ieeecomputersociety.org/10.1109/FGR.2006.96 db/conf/fgr/fgr2006.html#LiAHL06