Vector error diffusion with edge control

An image processing system that is operative to transform a color contone description of an image into a reduced quantization version of the image according to a desired edge modification, the system comprising:

• a pixel value combiner that is operative to receive contone pixel values of target pixels of the image which call for colorant densities of a plurality of colorants of an associated image rendering device, the plurality of colorants including a first colorant associated with at least a first pixel value of the target pixel and a second colorant associated with at least a second pixel value of the target pixel, to receive contone color error values associated with marking decisions made in regard to a previously processed contone pixel of the image or initial contone error values and to combining the contone pixel values with the contone error values, thereby generating a sets of error modified pixel values;
• a marking decision selector that is operative to select marking decisions based on the sets of error modified pixel values and at least one function of at least one of the received contone pixel values of the target pixels, wherein an error modified pixel value of a target pixel associated with at least the first colorant is a factor in selecting a marking decision regarding at least the second colorant of the target pixel, wherein marking decisions for a given pixel may sacrifice color accuracy in favor of placing a mark for a given set of error modified pixel values and wherein the at least one function biases the marking decision associated with a respective error modified pixel value toward making a mark as a respective value of the received contone pixel values increases in darkness when the desired edge modification is an edge enhancement and wherein the at least one function biases the marking decision associated with a respective error modified pixel value away from making a mark as a respective value of the received contone pixel values decreases in darkness when the desired edge modification is an edge attenuation;
• and
• a color error determiner that is operative to determine color error associated with each selected marking decision and make contone color error values describing the determined color error available for the processing of at least one subsequently selected target pixel.

A method for transforming a color contone description of an image into a reduced quantization version of the image according to a desired edge modification, the method comprising:

• defining a marking decision color space that relates sets of color contone pixel values to sets of reduced quantization marking decisions regarding the plurality of colorants, the marking decision space being defined, at least in part, by respective reference points, the respective reference points being those points in the marking decision space that correspond to respective extremes of a range of available contone pixel values and therefore corresponding to marking decisions associated with zero marking decision error for the respective corresponding pixel values, the marking decision space definition associating respective subsets of sets of contone pixel values with the marking decision associated with respective ones of the respective reference points based on respective functions of distance in the color space of points identified by the sets of contone pixel values to respective ones of the respective reference points;
• and
• for each contone pixel in the image, selecting the contone pixel as a target pixel:
• receiving contone pixel values of the target pixel of the image which call for colorant densities of a plurality of colorants of an associated image rendering device, the plurality of colorants including a first colorant associated with at least a first pixel value of the target pixel and a second colorant associated with at least a second pixel value of the target pixel;
• receiving contone color error values associated with marking decisions made in regard to at least one previously processed contone pixel of the image or initial contone error values;
• combining the contone pixel values with the contone error values, thereby generating a set of error modified pixel values;
• combining at least one value of the error modified pixel values with a respective value of at least one function of at least one value of the received contone pixel values of the target pixel, thereby generating a warped error modified pixel value;
• identifying a point in the marking decision color space corresponding to the warped error modified pixel values;
• selecting marking decisions associated with the identified point according to the identified point
• determining color error associated with the selected marking decision;
• storing the determined color error for use in processing a subsequent pixel of the contone image;
• and
• at least one of storing or rendering the selected marking decisions;
• thereby transforming the image into a reduced quantization version of the image.