Patent ID: 7564589

Claim:
A color error diffusion 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) using a computer to determine output levels for each color channel using a process that includes a quantization step that produces intermediate error values and an error sorting step that is applied to the intermediate error values; b) determining error signals for each color channel responsive to the input levels and output levels; c) producing first error signal offset values that are a function of the input levels of the input pixel and producing shifted error signals by adding the first error signal offset values to the error signals for each color channel; d) weighting the shifted error signals for each color channel by a set of error feedback weights to determine weighted error signals for nearby pixels that have yet to be processed; e) producing additional error signal offset values that are a function of the input levels of the corresponding nearby input pixels and producing shifted weighted error signals by adding the additional error signal offset values to the weighted error signals for each color channel; f) adjusting the input levels for the nearby pixels responsive to the shifted weighted error signals; and g) repeating steps a)-f) for multiple input pixels of the input digital image to thereby provide the output digital image.