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The Practical Relationship Retwreen in a tn ni a and Visual Contrast
By S. D. Lund
Laboratory Division. Universal Studio
T7 very industry has at one time or -^another undergone changes brought about by the application of new principles or inventions. In the case of the motion picture, such a change took place when sound, and especially filmrecorded sound, was introduced.
One of the most significant of these changes was in the field of laboratory processing methods. The necessity for faithful sound reproduction — the fact that the photographic quality of the sound-track print must he an exact replica of that of the sound negative if good sound is to be heard -caused a major revolution in the methods of the industry’s film-processing laboratories. The rather loose methods which had previously sufficed, based as they were largely on visual inspection and personal skill and judgement, were not sufficiently accurate for this purpose. and as a result the more accurate methods of sensitometric control were substituted.
This brought a host of new and hitherto unfamiliar technical terms and phrases into the picture. Some of them still seem perplexing and unnecessarily complicated to many cinematographers, since they seem in some
cases to substitute new and complex values for the terms with which the industry grew up. It is the purpose of this article to attempt a simple translation of some of them into the more familiar terms of everyday photographic practice.
Chief among these terms are cryptic references to “the H. & D. Curve” and to “Gamma.”
Basically, these are simple enough, if one will simply consider the former as a skctch-map of the latitude and contrast characteristics of a film and the latter as a numerical expression of contrast.
Every practical photographer knows from experience that with any type of film there is a definite relation between the exposure given and the density produced. Within certain limits, an increase in exposure brings a corresponding increase in density. But in the very low exposure ranges, and in the very high exposure ranges, this does not hold good. In the low region, that is, in the extreme lowest shadows, the exposure has to increase a lot to make a relatively small increase in density. In the very high region — the extreme "hottest” highlights — most
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