Method for colorizing a digital halftone

Abstract

An improved method for colorizing a digital halftone that uses both input color density and output halftone luminance to quantize and relocate color thereby reducing digital storage and transmission overhead capacity. The method utilizes a synergy between color and luminance inherent within the input image to enable the available space for color within the output luminance halftone to not exceed that necessary to allocate all of the input color information. An input color image is digitally reproduced using a separation of input primary color information from input grayscale information. A digital halftone, derived from the grayscale or luminance channel of a four-channel input image, is colorized by the invention's method of processing the remaining three additive or subtractive primary color channels. The halftone's two output colors are designated 'black' and 'transparent.' The three color channels are combined, quantized and assigned to localized output bitmap segments each described by three bits, one for each primary color. Each segment's three-bit descriptor is assigned to all transparent pixels contained within the corresponding multi-pixel cell of the digital halftone. As a result, output file size is decreased while relative accuracy of color placement is maintained. Both the original halftone file and the colorization file then may be stored or transmitted following which they are combined for display by a computer monitor or printer.