Recently, there has been an increase in the use of video and statistical data in sports practice and coaching. A player-tracking function plays an important role in order to obtain players' trajectories which are essential for performing statistical analyses of players. Usually, in video-based tracking systems, sensor cameras are mounted to ceiling to prevent players from overlapping on the image, because the overlapping makes it difficult to detect overlapped further players, which may lead wrong trajectories. So, the ceiling cameras are useful for tracking but it is expensive to mount on ceiling, thus a system using wall-mounted cameras that can be installed at low cost is desired. However, wall-mounted cameras cause a problem that players may overlap each other on the image. To overcome this problem which is inevitable for such wall-mounted camera systems, we propose a stable tracking method which determines the position of the player having less overlapping ratio earlier and determines ones having more overlapping ratio later with using previously determined players' positions. The overlapping ratio is defined by using the positional relation between the target player and one's surrounding players from all of those images where the target player exists. Experimental results with real basketball scenes show that the positional error is less than 15cm, and the processing time is less than 10ms/frame at 3.0 GHz CPU, which proved that our method has enough performance for using real-time player tracking system.
