DENSITY-DEPENDENCE OF HIGH-FREQUENCY WIENER SPECTRA OF RADIOGRAPHIC MOTTLES MADE USING RARE-EARTH SCREEN-FILM SYSTEMS

An optical system for obtaining high-frequency behaviour of the Wiener spectra of radiographic mottle was installed. This system was constru cted from a high-power He-Ne laser, a focussing lens, a zoom lens, and a recording system. The Fourier-transform action of the zoom lens was utilized. Spatial frequency range was changed by changing various fac tors. The density dependence of the Wiener spectra of radiographic mot tle, made using typical rare-earth screen-film systems, was easily obt ained using the optical system but the spectral values were relative. The high-frequency spectral curves were connected to the absolute low- frequency spectral values obtained from microdensitometric traces. Thu s the spectral values up to 200 mm-1, even for high-density films, wer e obtained. At frequencies of more than about 30 mm-1, only the film g ranularity existed. As the average density decreased, the Wiener spect ral values were smaller and decayed faster.