Frequency Dependence of Minimum Perceptible Contrasts of Radiographs under the Glare of a Viewer

Abstract

The frequency dependence of minimum perceptible contrasts (differences in diffuse density units) was obtained by observing noiseless sinusoidal patterns placed at the centre of a viewer. The glare around the test piece disturbed the perceptibility. The contrasts increased at high densities by the effect of glare. This effect was appreciable for high frequencies. For frequencies higher than 1 mm^-1, the results were explained by the adaptation luminous exitances calculated by the Stiles-Crawford formula. For lower frequencies, the perceptibility was better than the calculated results. Optimum densities decrease under the disturbance of glare