LINEAR I'KKDK TION IN TELKVISION 



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ther explanation — namely, "previous value," "slope," "previous line," 

 "planar" and "circular." 



"Previous value" prediction is illustrated in Fig. 5. Here the prediction 

 is taken to be the signal amplitude of the preceding picture element. 

 The pre^'ious amplitude of the signal, »Si.o is subtracted from the present 

 value of the signal, So.o . The error signal is given as 



e = 'jo.o — Si^a 



The filter characteristic can be expressed as 



F(a,) = 



(2.i„^).' 



-\ Ai - "i) 



This method of prediction proves to be rather effective in reducing the 

 average power for most television pictures. The expression for the filter 

 characteristic given above shows that the peak amplitude can be twice 

 that of the original signal. 



"Slope" prediction is illustrated by Fig. 6. "Slope" prediction is so 

 called because it is equivalent to passing a straight line through the 

 two previous signal values, with the assumption that this line will pass 

 through the next signal value. The predicted signal is given by 



Sp = 2oi,o — 'J2,0 



The frequency and phase characteristic is expressed as 



i^(co) = [4 sin2 o)T]e 



i(7r— ut) 



For this method of prediction, the peak amplitude of the error signal 

 can be as much as four times the peak amplitude of the original signal. 



Fig. 5 — Example of "previous value" prediction, where the error signal is the 

 difference between the actual value of the signal and the previous value. 



