On the Evaluation of Strongly Enlarged Photographs

摘要

The accuracy of the evaluation of a photographic plate is limited by its grain structure. One approximates the value for the light density at a given point by the average light density in a small area (the 'test area') surrounding the point. The paper establishes confidence limits for evaluation procedures of this kind. It is assumed that the grains on the photographic plate arise in independent random processes controlled by the local density of the light flux. In the evaluation procedure one counts the number of grains in the test area. Generalizing the method one attaches to each grain a weight factor depending upon the grain position within the test area and then determines the sum of the weight factors for the grains found in the test area. By such a procedure one can determine quantities related to the light density, e.g. the density gradient; one also can scan for patterns of a special kind, e.g. a sudden jump of the light density. There are two kinds of errors due to the randomness inherent in the process of grain generation. The variance due to errors of both kinds must be minimized. (Author)