LINEAR PREDICTION IN TELEVISION 



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relation is pvidout in both space and time. Briefly, correlation is that 

 relation which the "next" elemental part of the signal has with its past. 

 To lea\e correlation in a, message is to be I'edundant, and this effec- 

 tively loads the transmission medinm with a lot of excess "words" not 

 necessar}' to the description of the picture at the receiving end. It is 

 then more "efficient" to send only the information necessary to identify 

 the picture, and to restore the redundancy at the receiver. 



EFFICIENT TR.\NSMISSION 



The more efficient we are in sending pictures over a given transmission 

 line, the more alarmed we become at the increasing amount of equipment 

 that is required at the transmitting and receiving terminals. Cei'tainly 

 the design wll be a compromise between the complexity of apparatus and 

 the efficiency achieved. The ingenuity of engineers will be taxed along 

 these lines for years to come; however basically, the general form of 

 these systems will be similar to that shown in Fig. 1. Although not 

 always separable, four essential operations are required-namely, decor- 

 relating, encoding, decoding and correlating. The transmitting decor- 

 relator and the encoder encompass the principal design problems, since 

 the decoder and correlator at the receiving end perform the reverse 

 operations which interpret the code and add in the redundancy that was 

 removed. 



Decorrelation involves prediction, and as the predictors are more 

 nearly made to predict the future of the signal, the more the output 

 signal from the decorrelator resembles random noise. The essential 

 picture information is still present, which means that our original picture 

 signal can be obtained at the receiving end without theoretical degrada- 

 tion. The basic job of the encoder is to match the picture information 

 out of the decorrelator to the channel over which it is to be transmitted. 

 There are several encoding operations. The first concerns the rate of 

 information into the encoder, and that required out of it. In the case 

 of television, there are fiat, highly correlated areas as well as areas 

 containing more concentrated detail. This means that the information 



OUT 



Fig. 1— Block diagram of an efficient transmission system employing reversible 

 decorrelating and encoding means. 



