Production of color coded equidensities using nonlinear filtering

An optical method to generate a family of color coded equidensities from a continuous tone input is presented. A halftone screen technique is used together with the method of theta modulation to encode each density slice independently. The resulting coded image is demodulated in a spatial filtering system using a polychromatic extended source. With a simple screen, the method allows the number of slices and their density levels to be adapted to the input to be processed while a color code can easily be added to the processed output.