An Automatic Calibration Method Based on Feature Point Matching for the Cooperation of Wide-Angle and Pan-tilt-Zoom Cameras

Wide-angle cameras are used to monitor large open areas, but moving objects on the image are often too small to view in detail. However, pan-tilt-zoom (PTZ) cameras have zooming capabilities that can be used to capture close-up images of a moving object. Therefore, the cooperation of these two types of cameras has been studied extensively in recent years. A calibration method is necessary to achieve the above cooperation. For any coordinate on the image plane of a wide-angle camera, this calibration method is needed to obtain the corresponding pan, tilt, and zoom values, known as the point correspondence of the PTZ camera. It is inconvenient to manually establish point correspondences, as shown in previous studies. Therefore, an automatic calibration method is proposed in this paper. The method is mainly based on the matching of feature points on the images of wide-angle and PTZ cameras. A feature point (FP) is extracted based on several edge operators derived from a 2D Gaussian smoothing function. A two-phase FP match is then designed to obtain the point correspondences. In the study of a prototype for capturing close-up images of moving objects, the calibration process took approximately 7 minutes for 44 FPs. The average successful rate of the capturing tasks was 82 percent. It shows that the automatic calibration method is feasible for the cooperation of wide-angle and PTZ cameras.