Experiments with Linear Prediction 

 in Television 



By C. W. HARRISON 



(Manuscript received February 28, 1952) 



The correlation present in a signal makes possible the prediction of the 

 future of the signal in terms of the past and present. If the method used for 

 prediction makes full use of the entire pertinent past, then the error signal — 

 the difference between the actual and the predicted signal — will be a com- 

 pletely random wave of lower power than the original signal but contaiyiing 

 all the information of the original. 



One method of prediction, which does not make full use of the past, but 

 which is nevertheless remarkably effective with certain signals and also 

 appealing because of its relative simplicity, is linear prediction. Here the 

 prediction for the next signal sample is simply the sum of previous signal 

 samples each midtiplied by an appropriate weighting factor. The best values 

 for the weighting coefficients depend upon the statistics of the signal, but 

 once they have been determined the prediction may be done with relatively 

 simple apparatus. 



This paper describes the apparatus used for some experiments on linear 

 prediction of television signals, and describes the residts obtained to date. 



INTRODUCTION 



Linear prediction is perhaps the most expedient elementary means of 

 removing first order correlation in a television message. Before discussing 

 the advantages and disadvantages of linear prediction, it might be well 

 to consider what is generally meant by correlation in a tele\dsion pic- 

 ture and why it should be removed. 



Almost every picture that has recognizable features contains both 

 linear and non-linear correlation. Each type of correlation helps in 

 identifying one picture from another; however, linear prediction is only 

 effective in removing linear correlation, and for this reason, future ref- 

 erences to correlation ^\'ill refer only to its linear properties. With tele- 

 vision, a signal is obtained as the result of scanning; hence, the cor- 



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