Statistics of Television Signals 



By E. R. KRETZMER 



(Manuscript irceivcd February 28, 1952) 



Measurements have been made of some basic statistical quantities characteri- 

 zing picture signals. These include various amplitiule distributions, auto- 

 correlation, and correlation among successive frames. The methods of meas- 

 urement are described, and the residts are used to estimate the amount by 

 which the channel capacity required for television transmission 7nay be re- 

 duced through e.vploitation of the statistics measured. 



INTRODUCTION 



One of the teachings of information theory is that most communica- 

 tion signals convey information at a rate well below the capacity of the 

 channels proWded for them. The excess capacity is required to accom- 

 modate 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 

 remo\'e redundancy, one must first understand it; the amount and nature 

 of the redundancy can be completely defined in terms of various statis- 

 tical parameters characterizing the signal. 



It has been pointed out that the existence of redundancy is particularly 

 exadent in the case of television ; moreover, its elimination is highly de- 

 sirable because of the large bandwith presently required for transmis- 

 sion. Evidence of redundancy is found in the subject matter of televi- 

 sion — 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 pre- 

 diction about the next frame. In either case, knowledge of the past re- 

 moves uncertainty as to the future, leaving less actual information to ])e 

 ti'ansmitted. 



Another way of looking at this is to visualize the picture as an array 

 of approximately 210,000 dots, 500 vertically, 420 horizontally, cor- 

 responding, respectively, to the 500 scanning lines and 420 resolvable 



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