Method and apparatus for increasing the visibility of low-contrast images

Abstract

Method and apparatus for increasing the visibility of low contrast images. In accordance with the invention, the visibility of a selected area of an image is increased relative to another area of said image which differs only slightly in brightness from said selected area by causing said selected area to periodically vary in brightness while maintaining the brightness of said other area constant. The apparatus for carrying out the invention comprises an optical circuit including an electro-optic photosensitive storage device having a photosensitive characteristic in which the conductance of the device varies as a function of the intensity of the radiation incident upon it, and an electro-optic birefringent characteristic in which the birefringence varies as a function of an electric field applied across it. An image of an object is read into the device which is then read-out onto a screen by placing the device between two polarizers in a readout light beam. Additionally included between the polarizers is an optical retardation means capable of cyclically varying the retardation in the readout path between two chosen values. By cyclically varying the retardation between said chosen values, one area of the output image can be maintained at a constant brightness while all other areas of different original brightness will be caused to cyclically 'flicker' above and below the constant brightness level. This 'flicker' will make those areas more readily discernible.