Statistics of Television Signals

One of the teachings of information theory is that most communication signals convey information at a rate well below the capacity of the channels provided for them. The excess capacity is required to accommodate the redundancy, or repeated information, which the signals contain in addition to the actual information. Removal of some of this redundancy would reduce the channel capacity required for transmission, thus opening the way for possible bandwidth reduction. In order to remove redundancy, one must first understand it; the amount and nature of the redundancy can be completely defined in terms of various statistical parameters characterizing the signal. It has been pointed out that the existence of redundancy is particularly evident in the case of television; moreover, its elimination is highly desirable because of the large bandwith presently required for transmission. Evidence of redundancy is found in the subject matter of television--the average scene or picture. Knowing part of a picture, one can generally draw certain inferences about the remainder; or, knowing a sequence of frames, one can, on the average, make a good guess or prediction about the next frame. In either case, knowledge of the past removes uncertainty as to the future, leaving less actual information to be transmitted. Another way of looking at this is to visualize the picture as an array of approximately 210,000 dots, 500 vertically, 420 horizontally, corresponding, respectively, to the 500 scanning lines and 420 resolvable 751