Self-Recalibration of PTZ Cameras

Pan-tilt-zoom (PTZ) cameras have been widely used for providing flexible view selection and a wider observation range. In order to utilize these cameras for a meaning application, it is necessary to calibrate cameras. However, with camera pan, tilt and zoom, the previous calibrated camera parameters often vary, which are required to be updated automatically. In this paper, we present a novel self-recalibtion method of PTZ cameras under a small pitch angle. The proposed approach is based on the calibrated camera. First, the keypoints from two frames, corresponding to ones before and after the parameters are changed, are matched roughly, then the false matching pairs are removed by the displacement constraint, which is statistical displacement constraint in pan and tilt, while in zoom is principal point constraint. Second, the homography between the two frames can be estimated from the matching ones, then the camera parameters can be updated by combining previous known parameters. Furthermore, we present a evaluation method of recalibration precision. Experimental results demonstrate the effectiveness of the proposed algorithm.