The Earth Resources Technology Satellite (ERTS) system produces a large volume of images of the Earth, with exposed film as the final output. These Images are presented to the user in pictorial form for interpretation and analysis. Specifications for this output film include MTF requirements, development method requirements, geometric tolerance and the number of DDL\u27s (distinguishable density levels). Given the specification of 64 levels of gray, with a minimum density range of 2.0, the following investigation is warranted. Using theoretical calculations, granularity will be determined at different density levels. Assuming that Selwyn\u27s Law is valid for the range of apertures and films in this specific investigation, granularity as a function of density will be calculated. Further, assuming these calculations are valid, a procedure will be established by which films can be selected for the ERTS project, solely on the basis of these calculations. Several experiments were performed to evaluate the merit of the theoretical calculations. The results were similar, however inconclusive. A series of experiments were performed in attempt to establish a new measure by which the films could be judged. The sum of the variations caused by granularity, area to area variation and pixel to pixel interaction were generated with this new technique
