Comparison of Wiener spectra of quantum mottle for screen-film systems with modulation transfer functions

Rossmann proposed that the Wiener spectrum of the quantum mottle was proportional to the square of the modulation transfer function(MTF) of the screen-film system. On the other hand, Lubberts pointed out that the shape of the Wiener spectrum of the quantum mottle depended on the sum of the squares of the MTFs for different depths in the screen phosphor layer, rather than the square of the sum of the MTFs for the different depths, i.e., the square of the MTF of the screen-film system. The purpose of this study is to experimentally investigate the proportionality between the Wiener spectrum of the quantum mottle and the square of the MTF of the screen-film system using two screen-film systems having different screen thicknesses. For the purpose, we determined correction factors for the square of the MTF of the screen-film system in the Wiener spectrum of the quantum mottle, that is, the ratios of the sums of the squares of the MTFs for different depths to the squares of the MTFs of the screen-film systems so that the theoretical Wiener spectral values of the screen mottle fitted the experimental values. For the thin screen, the correction factors were unity for all spatial frequencies, that is, the Wiener spectra of the quantum mottle were proportional to the square of the MTF of the screen-film system. On the contrary, for the thick screen, the factor increased with the spatial frequency, that is, the Wiener spectra were proportional to the sum of the squares of the MTFs. Therefore, we can conclude that the relation between the Wiener spectrum of the quantum mottle and the MTF of the screen-film system, for thin screen, agrees with Rossmann's theory, whereas, for thick screen, agrees with Lubberts' theory.