Equidensitometry by coherent optical filtering

A new and simple method has been developed for fabrication of multilevel halftone screens that have proved useful for generation of equidensity contours by means of coherent optical filtering. Up to ten contours of constant brightness have been generated on a picture by coherent optical filtering of a single halftone copy of that picture. The possible application of this method to optical analog-to-digital conversion using a single halftone photograph is discussed.