An Instrument for the Measurement of the Graininess of Photographic Materials *†

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Abstract
The term “graininess” as applied in this paper refers to the subjective factor which has been well defined by Jones and Deisch as: “the sensation or impression of nonuniformity in a photographic deposit, produced upon the consciousness of the observer when such a deposit is viewed.” The physical aspect of the problem, that is, the size of the ultimate silver grains, the size frequency and the number of grains per given area, has been defined in this laboratory as “granularity” and in this paper the term will be so used. Jones and Deisch used a method of measurement in which the observer determined the distance at which a magnified image of the deposit ceased to appear as nonhomogeneous. This is essentially the same as measuring the necessary magnification when the viewing distance is kept constant. It is the latter method which has been applied in the design of the instrument to be described. A number of methods for the measurement of graininess have been proposed at various times, among which have been the so-called physical methods, such as the measurement of Callier’s “Q” factor or the scanning of the silver deposit and recording its nonhomogeneity by means of the response of a photoelectric cell or other light-sensitive device. These methods measure the granularity of the deposit rather than its graininess. In the last analysis the point of chief interest is the effect upon the consciousness of the observer, and so far as present knowledge is concerned a subjective method is the only one which gives promise of direct interpretation. Following the description of the apparatus and the defining equation some results showing the relation between field brightness and graininess are given for a range of brightnesses from 6 to 100 millilamberts. Data showing the effect of constant field brightness upon the graininess of several different emulsions are presented and a proposal for applying the results to the problem of graininess measurement is made. Results are also included on Q factor determinations as a measurem nt of graininess, together with a description of the apparatus used for this investigation.

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