Journal of the Society of Motion Picture Engineers (1930-1949)

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at the good signal-to-noise ratio they have been able to obtain. By scrupulous attention to every element in the chain they have been able to preserve a good relationship between contrast in the object and in the image photographed on film up to the highest resolution powers of which the system is capable. They are confident that this result is capable of extension to higher definition by expedients which they hope to describe in due course. It should be mentioned in passing that particular attention has been given to the design of kinescope recording tube screens so as to maintain high contrast at the finest detail and eliminate as far as possible reflections and diffusion effects which militate against the desired result. (e) The factor attributed to Kemp was omitted from the published version of his paper. (f) The acceptable ratio between signal and noise seems to depend largely on the nature of the noise. The authors took a number of examples of optically produced film exhibiting normal grain structure and made a series of statistical tests against television picture recordings on fine-grain film in which the noise was of a fairly high-frequency type. When the two results were adjudged to be as nearly comparable as could be determined by observation, the level of peak noise in the television picture was found to be some 30 db below peak white. Had there been a preponderancy of lowfrequency noise in the television picture it is highly probable that some ratio of the 40-50 db order would have been required, because not only is the highfrequency noise attenuated in the photographic process, but it is less apparent to the eye because of its finer structure. As regards shading and phase distortion, the authors have worked to a condition of no visible shading in the photographic image, but with a progressive increase in brightness towards the edges of the picture amounting to some 15% at the extremes to compensate for lens vignetting. It has been found advantageous in some cases to overcorrect the final product to compensate for the projector objective. Phase compensation throughout the system is advocated so that no visible overshoot occurs at any frequency within the limits of the response of the system. (g) The authors regret that they cannot quote any scientific evidence regarding the greater incidence of vertical as opposed to horizontal edges in a natural scene, but they have frequently heard the view expressed that the former tend to preponderate. In conclusion, the question of nicker on the director's viewing screen has proved curiously unimportant. At a brightness consistent with fairly low levels of ambient illumination the flicker is singularly inobvious and after a few minutes the observer gets used to it and forgets it entirely. The wearing of dark glasses has been recommended and certainly assists in this connection, but never at any time during the authors' work has any serious complaint of flicker been voiced. Reproducing tubes having a moderate decay are used at present and the development of tubes having some approximation to a square decay has made some advance. Unfortunately, however, no information can be disclosed on such tubes at the present time for security reasons. Collins and Macnamara: Electronic Camera 461