Restoration of retinal images obtained through cataracts

An optical model for imaging the retina through cataracts has been developed. The images are treated as sample functions of stochastic processes. On the basis of the model a homomorphic Weiner filter can be designed that will optimally restore the cataractous image (in the mean-square-error sense). The design of the filter requires a priori knowledge of the statistics of either the cataract transmittance function or the noncataractous image. The cataract transmittance function, assumed to be low pass in nature, can be estimated from the cataractous image of the retina. The statistics of the noncataractous image can be estimated using an old, precataractous photograph of the same retina, which is frequently available. Various modes of this restoration concept were applied to clinical photographs and found to be effective. The best results were obtained with short-space enhancement using averaged short-space estimates of the spectra of the two images.