Tracking head positions in three-dimensional space by using a single omnidirectional camera

We propose a novel method using a single catadioptric omnidirectional camera to track 3-D head positions in nonintrusive biometric systems. Existing methods have not been able to deal with cases in which the ground plane is nonorthogonal to the optical axis of the camera. To overcome this problem, our proposed method presents the following three improvements: (i) By using 1-D tracking of the feet and head positions combined with a circular constraint in images instead of conventional 2-D tracking methods, the accuracy and computational efficiency of the tracking process is significantly improved, (ii) based on the detected 2-D head position in images with the precalibration information of the camera, the 3-D head positions can be obtained, and (iii) the 3-D head positions can be obtained without having the optical axis of the camera orthogonal to the ground plane. This makes the proposed method feasible in practical environments that use omnidirectional camera systems. Experimental results showed that the proposed method was able to track 3-D head positions at real-time speed.