Scans in Measuring Wiener Spectra for Photographic Granularity

Abstract

The Wiener spectrum obtained in one dimensional scanning method is proved theoretically to be given as an integral of the two dimensional Wiener spectrum along one spatial frequency axis perpendicular to the scanning direction. This relation is verified experimentally by studying the changes of the Wiener spectrum affected by slit widthes of a scanning aperture. The slit width along the scanning direction determines the frequency pass band of the Wiener spectrum, and the slit width perpendicular to the scanning direction determines the sectional area of two dimensional Wiener spectrum. A new granularity factor (b·\varPhi _m (ν)=c o n s t. for a given film) is suggested as an objective measure for the photographic granularity, where b is the slit width perpendicular to the scanning direction and \varPhi _m (ν) is the Wiener spectrum at the spatial frequency ν. This simple formula similar to the Selwyn relation is confirmed theoretically and experimentally to be valid, when b is large enough.