English

Abstract

In this paper, we propose a high-performance object tracking system for obtaining high-quality images of a high-speed moving object at video rate by controlling a pair of active cameras that consists of two cameras with zoom lens mounted on two pan-tilt units. In this paper, “high-quality image” implies that the object image is in focus and not blurred, the size of the object in the image remains unchanged, and the object is located at the image center. To achieve our goal, we use the K-means tracker algorithm for tracking objects in an image sequence captured by the active cameras. We use the results of the K-means tracker to control the angular position and speed of each pan-tilt-zoom unit by employing the PID control scheme. By using two cameras, the binocular stereo vision algorithm can be used to obtain the 3D position and velocity of the object. These results are used in order to adjust the focus and zoom. Moreover, our system allows the two cameras to gaze at a single point in 3D space. However, this system may become unstable when the time response deteriorates by excessively interfering in a mutual control loop or by strict restriction of the camera action. In order to solve these problems, we introduce the concept of reliability into the K-means tracker, and propose a method for controlling the active cameras by using relative reliability. We have developed a prototype system and confirmed through extensive experiments that we can obtain focused and motion-blur-free images of a high-speed moving object at video rate.