HALFTONE SCREEN TECHNIQUES FOR PHOTOGRAPHIC FILM RESPONSE SHAPING WITH APPLICATION TO OPTICAL-PROCESSING OF MEDICAL X-RAY IMAGES

Optical image processing is notoriously sensitive to nonlinearities in the input medium; many otherwise successful optical processors fail to perform adequately outside the laboratory environment because of this problem. The usual solutions to the problem-use of special photographic emulsions, developers, and even preexposure (bias)-severely limit the applicability of many optical processing schemes and may also degrade the SNR of the input image. We present several methods, all using halftone screens, to obtain proper response from the input photographic film. We then demonstrate one particular method, both theoretically and experimentally, as applied to x-ray recording of coded images that are to be used as input for an optical transaxial tomography processor. © 1979 Optical Society of America.