Patent ID: 7362472

Claim:
A method for multi-toning an input digital image having input pixels with two or more color channels, each color channel, C, having a specified number of input levels, N i , to form an output digital image having modified output levels, each color channel of the output digital image having a specified number of output levels, N o , where 2≦N o <N i , comprising: a) quantizing the input level for each color channel of a pixel in the input digital image to determine a quantized output level for each color channel; b) producing an error signal for each color channel representing a difference between the input level and the quantized output level; c) summing the error signals for each color channel to produce a combined error signal representing a total number of additional output level increments; d) sorting the error signals for each color channel to produce a set of sorted error signals; e) determining modified output levels for each color channel by modifying the quantized output levels for the color channels having the largest magnitude sorted error signals, wherein the number of color channels to be modified is determined from the combined error signal; f) producing a modified error signal for each color channel responsive to the input level and the modified output level; g) weighting the modified error signals for each color channel by a set of error feedback weights and adjusting the corresponding input levels for nearby pixels that have yet to be processed; and h) repeating steps a)-g) for every input pixel of the input digital image to thereby provide the output digital image.