Patent Document ID: 8077917
Application ID: 11917741
Patent Status: 1

Claim One:
1. A system for producing a video signal representing a sports scene wherein, during at least a period, a ball moves in front of an essentially static background, the system comprising: an image recording means adapted to register a series of source images of the scene; a tracking means adapted to track a path of the moving ball through at least a sub-set of the images in said series, the tracking involving a differencing between consecutively registered images wherein image areas are identified that have been updated in a later registered image in relation to an earlier registered image; and a graphics generator adapted to, based on said source images, generate a composite image sequence wherein synthetic image elements are combined with the images in said series, such that a trace representing the path of the moving ball is shown in the form of added image data successively overlaid the image contents of the images in said series, wherein the tracking means is adapted to automatically identify an initial image position for the moving ball by: producing, for each image in said series, a difference image between the image and an image subsequent thereto, wherein in the difference image all image elements representing a contents alteration below a threshold level are allocated a first value, and all image elements representing a contents alteration above or equal to the threshold level are allocated a second value, identifying a set of ball candidates in which each ball candidate is represented by a group of neighboring image elements which all contain the second value and said group fulfills a ball size criterion, and selecting the initial image position from the set of ball candidates based on a ball selection algorithm, wherein the ball selection algorithm implies a stroke estimation procedure wherein the ball candidates in the set of ball candidates are analyzed in three consecutively registered images, the stroke estimation procedure comprising: defining a respective path candidate line extending straight between each ball candidate in a first registered image and each ball candidate in a third registered image, discarding each ball candidate for which, in a second image registered between the first and third registered images, no ball candidate is found within a threshold range from the path candidate line, and defining a tentative ball path for all other path candidate lines.