Patent ID: 8098403

Claim:
A color printing system having two or more color channels, each color channel having a specified number of printable output levels, N o , for printing input digital images having input pixels with corresponding color channels having a specified number of input levels, N i , where 2≦N o <N i , comprising: a printing module for printing colorant for the two or more color channels onto a receiver medium; a data processor; a program memory communicatively connected to the data processing system and storing instructions configured to cause the data processing system to implement a error diffusion method, wherein the color error diffusion method includes: 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; i) repeating steps (a)(-h) for multiple input pixels of the input digital image to thereby provide an output digital image, which is different than the input digital image; and j) printing the output digital image using the printing module.