Journal of the Society of Motion Picture and Television Engineers (1950-1954)

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716 COLOR SENSITOMETRY June The known methods of color sensitometry do not provide exact objective specification of the best possible printing of a color negative or positive. Picture judgments are required to specify the final printing adjustments. But sensitometry has these important functions in printer operation : (1) Specification of printer conditions required for a given negative to a precision sufficient to provide first approximations from which further corrections can be confidently predicted by picture judgments. (2) Specification of printer changes to minimize differences among print film stocks. (3) Specification of printer changes to produce a known desired effect. The efficient use of sensitometry in these functions requires establishment of correlations between printer changes and negative characteristics (assuming a negative-positive process), and between printer changes and print-image characteristics. Theory suggests that the correlations will be most direct when printing densities are used for the former, and equivalent neutral densities for the latter. Most of the sensitometry involved in printer adjustment will make use of a camera-exposed image of a gray scale on the negative material to be printed. For initial adjustment, it may be assumed that this scale is to be reproduced as gray (at least in its middle tones). A trial print which is not gray can yield sensitometric information adequate for approximate correction. The separations of the equivalent neutral density" curves of the reproduction define the corrections to be made in the relative exposures of the red-, green and bluesensitized components. They will also show what step of the negative gray scale is being reproduced at the density which is assumed correct for reproduction of white. Printing densities of the negative gray scale will reveal the differences between the densities of this step and of the step corresponding to white. The printer is to be adjusted in accordance with these differences. These adjustments, or possibly a second round of them, will set the printer well enough to make a series of trial picture prints. When the best possible picture print has been made and chosen, a record can be made of the sensitometric characteristics of the corresponding gray scale. This correlation, corrected and extended by subsequent experience, will serve as a practical guide in making trial prints based on printing density measurements of other camera-ex