Abstract
It is shown experimentally that, although the granularity correlogram of a uniformly exposed and developed black-and-white photographic emulsion ordinarily extends only over a correlation distance equal to the diameter of the scanning aperture, correlation is exhibited over significantly greater distances when clumping is produced, e.g., by exposing to x-rays or developing to a high density. The difference between the effects produced by large and small scanning apertures is discussed, and it is shown that the variance for one aperture size cannot always be predicted from the variance for another. The procedure for combining the correlogram of a negative as affected by the printing procedure with the correlogram of the positive stock to give the correlogram of the print is discussed with examples. In the appendix, it is shown that the ordinates of the correlogram of the negative, as transferred to the print, are proportional to the square of the gamma of the positive stock and to the density of the negative. The importance of knowing the behavior of the microphotometer used to obtain the correlograms is demonstrated by a practical example.
© 1959 Optical Society of America
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