Fading:in of white spot into video telephone picture - uses light pencil applied first to bright spot near required point and then moved to that point

摘要

The fading uses a light pencil with a photoresistor, or a similar photosensitive cell, and the spot can be seen on screens of both subscribers. The pencil is attached to a coordinate input device which determines the position of the spot on the screen, when the photoresistor at the light pencil tip touches the screen. When a black area exists at the point where the white spot is to be faded-in, the photoresistor is at first applied to a brighter point of the picture near the point to be marked. The white spot so produced on the screen excites the photoresistor by optical feedback to generate a white spot, when the pencil is moved to the point where the spot should be produced.