Patent ID: 8199199

Claim:
A method for real time judging boundary lines on a tennis court in order to determine whether a tennis ball in play bounces in or out of said court, said method using radiation at least one video camera outputting a video image of said court, said method using at least one said video camera sensitive to near-infrared radiation, and said method using at least one point source of near-infrared radiation, illuminating said court and displaced relative to said at least one video camera, said method comprising: continuously obtaining frames of the video image of said court; within said frames of the video image, locating moving objects; comparing said moving objects to previously calibrated images of said tennis ball and its shadow from said at least one point source of near-infrared radiation so as to filter out any moving object which is not said tennis ball or its shadow and to distinguish said tennis ball and its shadow; fitting a path of said tennis ball and a path of its shadow into two independent trajectories correspondingly; detecting a spot on said court where said tennis ball bounces by locating a point of intersection of said two trajectories; determining whether said tennis ball is in or out of the court by comparing coordinates of said spot with a location of previously calibrated boundary lines of the court; and generating an output signal if said tennis ball is determined to be out of the court, wherein said step of comparing said moving objects to previously calibrated images of said tennis ball and its shadow from said at least one point source of near-infrared radiation so as to filter out any moving object which is not said tennis ball or its shadow and to distinguish said tennis ball and its shadow, and said step of fitting a path of said tennis ball and a path of its shadow into two independent trajectories correspondingly, further comprise: in a digital image of moving objects, an amplitude of every non-zero amplitude pixel is set equal to zero, if said pixel does not have approximately equal amplitude pixels around it in a circle having said pixel in the center of said circle, and said circle having a radius approximately equal to the radius of the image of said tennis ball; an amplitude of each remaining non-zero amplitude pixel is set equal to zero, if there are no pixels with the same amplitude in closest proximity of said each remaining non-zero amplitude pixel; and remaining two arcs of pixels of higher and lower amplitudes are considered trajectories of said tennis ball and its shadow correspondingly.