476 



BELL SYSTEM TECHNICAL JOURNAL 



Thus for motions in the picture which are not too fast to be expected to 

 be reproduced with reasonable fideHty, this diffuseness of the funda- 

 mental lines and their satellites will not obliterate their identity. 



A diagrammatic arrangement of some of the possible lines in a fre- 

 quency spectrum, with their corresponding m and n indices, is shown 

 in Fig. 7. 



It is important to note that the correlation between the wave lengths 

 of the field components and the frequencies of the current components 

 is not the one that is naturally assumed on first consideration. We 



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o — OJ t*! 



ro (M — o — 



FREQUENCY 



Fig. 7 — Diagram of signal frequency spectrum. 



are quite likely to make the erroneous assumption that high frequencies 

 correspond to all sharp changes in brightness and that low frequencies 

 correspond only to slow changes. The error in this assumption is 

 readily realized by noting that sharp changes in brightness may gener- 

 ate very low frequencies if the scanning point passes over them in a 

 sloping direction. An actual correlation is shown schematically in 

 Fig. 8. It is seen that the same general type of correlation is repeated 

 periodically over the frequency scale at multiples of the line scanning 

 frequency. There are evidently numerous regions of the spectrum in 

 which short image waves, or fine grained details of the image field, may 

 appear in the signal. They are not confined to the high-frequency 

 region alone. 



