Abstract
The optical image of a chart, seen through a diffusing screen, decreases its contrast as the distance between the diffusing screen and the chart is increased. If the diffusing screen, especially of small diffusibility, is moved farther away, the image becomes sharper and increases its contrast again. The former image of poor contrast is due to diffuse light in proportion to intensity distribution and the latter one of sharp contrast to direct light. In case of the diffusing screen moved apart, the intensity of diffuse light decreases gradually, but the intensity of direct light remains constant. Intensity distribution curves of diffuse light, emitted from one point of the diffusing screen, can be given approximately by an error function, and in case of the diffusing screen that produces reappearance of sharper image, the direct light component is superposed to the error function. The contrast transfer function in case of reappearance decreases quickly in gain near zero spatial frequency and the decrease stops.
