黑白胶片噪声测定方法的研究

本文采用实验测定和计算机模拟的方法,研究了黑白胶片的宏观噪声与微观噪声的性质及其相互关系。实验结果表明,黑白胶片的宏观噪声通常大于微观噪声,这是由于宏观噪声包括了胶片的宏观不均匀性的影响,而微观噪声则反映了由乳剂性质所决定的密度的统计涨落。因此,宏观噪声(相当于均方根粒度)适于用做感光材料的评价,而如果要研究卤化银乳剂的性质对影像质量的影响则微观噪声更有意义。在大面积范围内的多次测定结果表明,宏观噪声波动幅度较大,而微观噪声则重复性较好。实验结果表明,标准相关系数(r)在一定程度上可以作为感光材料宏观不均匀性的量度。

STUDIES ON THE METHOD OF DETERMINATION OF NOISE LEVEL OF BLACK-AND-WHITE PHOTOGRAPHIC MATERIALS

According to the recent studies on the noise character of photographic materials, two kinds of noise can be defined: the macronoise, σ_D (mac), and the micronoise, σ_D (mic). The macronoise is equivalent to the KMS-granularity of the photographic material, which is defined as and is belived to include the effect of large-scale nonuniformity of the emulsion layer. On the other hand, the micronoise, which is defined as is thought to be determined by the ultimate limit of the statistical fluctuation in the process of photon recording on the emulsion layer. This was verified experimentally and also by computer simulation. The results show that σ_D (mac) is generally greater than σ_D (mic), and the standard correlation coefficientis r=1-σ_D²(mic)/σ_D²(mac) greater than zero. This is apparently not due to the overlaping of the successive sampling spots. When the sampling rate was reduced from 50s^-1 to 11s^-1, which is equivalent to increase the distance between the successive sampling spots from 4.4 microns to 190 microns, the micronoise became close or equal to the macronoise, whereas the latter remained unchanged. 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 materrials, whereas the micronoise may be more meaningful when one ’s interest is on the influence of silver halide emulsion on the photographic image quality. The standard correlation coefficient may serve as a measure of the effect of large-scale nonuniformity of a photographic layer.