redundanzverringerungseinrichtung

摘要

In a conditional replenishment video system a coder selects only those samples from an input video signal which represent a significant change in amplitude for their corresponding spatial points within the video frame. A buffer memory in the coder stores the selected samples prior to their being transmitted to a receiving location. In response to an overload signal from the buffer memory, all selection by the coder is stopped for an interval at least as long as one video frame, and a special code word is coupled into the buffer memory. In a plurality of video frames following the cessation of all selecting, only those samples from the center area of the video frame are processed by the coder for transmission to a receiving location. Upon receiving the special code word, the receiver apparatus establishes a constant video amplitude at the edges of the picture outside of the center area. After the above-mentioned plurality of video frames has elapsed, the number of samples processed in each video frame is increased at a rate of one line of picture elements per frame along each edge of the center area of the picture until the entire video frame of samples is again processed by the coder. Visual indication that only the center area of the picture is being processed is given to the party in a visual-telephone system whose activity is causing a cropping of the picture either by means of a display device such as a pilot light or by means of a novel circuit in which the video picture which he sees of the other party is cropped by substantially the same amount as the picture which he is transmitting.