Abstract

Image enhancement potentially provides low-vision patients better use and enjoyment of printed photographs and TV. A variety of equipment and techniques exist for enhancements, but there is no systematic method of designing appropriate enhancement for low-vision patients. Most image enhancement techniques may be classified as either contrast modification or spatial-filtering techniques. Although global contrast modification may be beneficial for the visually impaired, there is no way to optimize the selection of the modification paradigm or the parameters to be used. We propose a linear model of impaired vision in which the degradation transfer function resulting from the impairment is described by the ratio of the spatial contrast sensitivity function (CSF) of the low-vision eye to the CSF of a normal eye. The inverse of the degradation transfer function may be used as a spatial filter to preemphasize the image before it is displayed to the low-vision patient. Based on the CSF, the appropriate filter may be tailored for each patient or group of patients. Both threshold and suprathreshold CSF data may be required for the filter design. Results with optically simulated cataracts indicate that this approach may be feasible for patients with high spatial frequency loss.

© 1985 Optical Society of America