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TECHNICAL EELATIONS 537
audience what technical arrangements are used to provide the images. At present, the advantage is with the motion picture, since television images are small* and of poor detail by comparison. It should be remembered that natural viewing by persons with normal vision provides sharp images with much detail; fuzzy images with poor detail tend to destroy the desired illusion and interfere with normal vision.
Technical Relations of Television and Motion Pictures
Film Scanning. Standard black-and-white television transmission calls for a line-by-line scanning of each picture frame to be transmitted. The present television frame frequency is 30 per second. The scanning is interlaced 2 to 1. The number of lines per frame is 525 ; no doubt this will be increased in the not-too-distant future.
In pickup, as in reproduction, the picture is scanned as a series of horizontal parallel lines from left to right (as the viewer faces the reproducing cathode-ray tube or screen). At the end of a scanned line, the trace returns quickly from left to right. The odd lines of the picture (1, 3, 5, 7, etc.) are scanned first ; when the right-hand edge of the bottom of the frame is reached, the trace quickly returns to the top left side where it begins scanning the even lines (2, 4, 6, 8, etc.) of the frame. The alternate scanning of the odd picture lines and the even picture lines is called 2-to-l interlace ; the purpose of interlacing is to reduce flicker viewed on the reproducing cathode-ray tube.
It cannot be assumed that the choice of any or all picture transmission parameters necessarily represent the very best possible. The use of 30 frames per second as the television frame frequency, as one example, would seem to have little scientific justification today. It would seem, rather ' ' a cure for a disease that no longer exists. ' ' About two decades ago it was hoped that the 60-cycle power line might be relied on for frame synchronization; accordingly, the frame frequency chosen was a submultiple of 60. Technical difficulties such as phasing and frequency drift were so serious that the power line synchronizing idea was abandoned; synchronization pulses are now transmitted as an essential part of the signal. There would seem to be no more justification for the selection of 30 frames per second than for any other. Because of the artistic relationships of the motion picture and television, there would be far more just justification for the selection of a multiple of 24 frames per
* There is unmistakable evidence that the buying public is beginning to consider the 10-inch tube television set too small despite its "loss leader" price.