we have this: an webcam, which is in front of a white wall. An dark oject is between the webcam and the wall. From this object we need (only) the coordinates of the top edges. This edge-coordinates (where background meets foreground) should be in a matrix (or whatever) to make an collision control.
At the moment we have the videoIn-signal, but we despair of getting coordinates out from this… please give us a hint how to go on!