Low-frequency Wiener spectra of radiographic screen-film systems

Wiener spectra of radiographic screen-film systems were measured in the low-frequency range from 0.05 to 0.8 mm-1 with a special photometric set-up capable of scanning large film areas with a very long slit. It appears that inhomogeneities in radiographic film and film processing produce a strong low-frequency component of the Wiener spectrum below approximately 0.4 mm-1. Similar disturbances over the whole measured frequency range less than 1 mm-1 can be introduced by technologically-caused inhomogeneities in radiographic screens (low-frequency screen noise). Low-frequency film and screen noise must be considered for calculation of the detectability, especially of large low-contrast details from Wiener spectral data.