A new approach to camera calibration with respect to a computer monitor is proposed. The camera location parameters, including three position and three orientation parameters, obtained from such calibration are useful for many virtual reality applications in which a camera is mounted on or located near the monitor to “look at” a user in front of the monitor. The calibration problem is solved indirectly by introducing an auxiliary tool, a pair of specially designed eyeglasses, with a laser pointer mounted on the nosepiece between the two glass frames. In the calibration procedure, the pose of the eyeglasses with respect to the camera is first computed analytically using the eyeglasses’ shape information, which is composed of two circles coming from the glass frames and two parallel lines coming from the nosepiece. Next, the line equations of the laser beams with respect to the camera are derived from the pose of the eyeglasses, and the relative position of a corner on the monitor plane with respect to the camera is computed from the information of the intersection of the two laser beam lines created by the laser pointer pinpointing the corner from two different places. After three corners’ positions with respect to the camera are computed, the plane equation of the monitor screen and the six location parameters with respect to the monitor are obtained. The proposed method is easy and practical for fast camera calibration, which is required each time the camera is moved. Experimental results show the effectiveness of the proposed approach. Three applications of the proposed method, namely, VR scene display, cursor control by the head direction, and face view rectification for preserving eye contact in video conferencing or Internet
telephony, are also discussed, with their respective mathematics derived in detail.
Pattern Recognition and Image Analysis (EI) 12 (1): 80-96