Patent US 3,961,133

An image generated by a television camera is combined with an image generated from digitally stored information to form a composite scene wherein objects appearing in either image properly occlude one another with respect to the eyepoint from which the scene is viewed. This is accomplished by processing the camera video signal to provide pulses for each raster line which indicate the starting and stopping points of an object viewed by the camera. At the same time, the camera video signal is provided on a delay line to a video switch which also receives the digitally generated video signal. The switch is controlled by logic circuitry in accordance with the established occlusion priority to pass to the video display device the proper signal from either the camera or the image generator.