On the Method of Determination of the Noise Levels of Black-and-White Photographic Materials

According to the recent studies on the noise characteristics of photographic materials, two kinds of noise can be defined: the macronoise, trD (mac), and the micronoise, aD (mic). The macronoise is the equivalent of the RMS-granularity of the photographic material, and is believed to include the contribution of the macroscopic non-uniformity of the emulsion layer. On the other hand, the micronoise is thought to be determined by the ultimate limits of the statistical fluctuation in the process of photon recoding on the emulsion layer. In this work, the above mentioned hypothesis was verified experimentally and also by computer simulation. The results showed that σ_D (mac) is generally greater than σ_D (mic), and the standard correlation coefficient, r, is greater than zero. This is obviously not due to the overlapping of the successive sampling spots. When the sampling rate was reduced from 50 s^-l to 11 s^-1 which is equivalent to increase the distance between the successive sampling spots from 52.4 microns to 238 microns, the macronoise remained unchanged, whereas the micronoise became close or equal to the macronoise. The computer simulation showed that the micronoise approaches the macronoise as the distance between the successive sampling spots increases. The authors suggested that the macronoise, i.e. the RMS-granularity, can be used as a figure of merit in the evaluation of photographic materials, whereas the micronoise may be more meaningful when one’s interest is on the influence of AgX emulsion on the image quality. The r-value may serve as a measure of the large-scale non-uniformity of a photographic layer.