Patent ID: 7982916

Claim:
A color error diffusion method for multi-toning an input digital image having input pixels with input levels for 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 output pixels with 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) determining intermediate output levels for each color channel by applying a quantization step to the input levels for the corresponding color channels of an input pixel; (b) determining intermediate error signals for each color channel responsive to the input levels and intermediate output levels; (c) determining an error signal offset value as a function of the input levels of the input pixel; (d) combining the error signal offset value and the intermediate error signals for each color channel to produce a combined error signal; e) sorting the intermediate error signals for each color channel to produce a set of sorted error signals; (f) determining output levels for each color channel of the output pixel responsive to the intermediate output levels, the combined error signal, and the sorted error signals; (g) determining error signals for each color channel responsive to the input levels and output levels; (h) weighting the error signals for each color channel to form weighted error signals and adjusting the input levels for the nearby pixels; and (i) repeating steps (a)(-h) for multiple input pixels of the input digital image to thereby provide the output digital image, which is different than the input digital image.