Reduction of false contours by chrominance modulation
AssigneeXerox Corporation
InventorSteven J. Harrington
Life of this patent
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Abstract
A system and method for eliminating luminance false contours within rendered documents by sacrificing chrominance accuracy within printer halftones and for using the reduction of chrominance to improve the luminance correctness for any requested color. Ordinary halftone processes are modified such that small hue shifts are traded off for the ability to eliminate luminance false contours. Luminances of colored inks are created in a manner that turns on only one color spot at a time, instead of all three, within a slowly changing gray area because numerically equivalent steps in chrominance are much less visible in printed form than changes in luminance. Removal of false contours is therefore achieved by chrominance variations rather than by spatial variations in a document.
Claims7
A method of reducing luminance false contours within printed documents by sacrificing chrominance accuracy within printed halftones, comprising:
- receiving initial color values for color specifications requested by an image processing system;
- determining a luminance error between said initial color values and typical luminance values produced by halftoning;
- determining a change in luminance for said initial color values which is the difference between said typical luminance values and a value of any next greater halftone levels;
- processing said luminance errors and said luminances to determine adjustment values for said initial color values;
- and
- determining new color specifications as a function of said adjustment values and said initial color values for said initial color values;
- wherein said new color specifications are provided to said image processing system to render documents displaying reduced luminance false contours within printed documents.
A system for reducing luminance false contours within a printed document, comprising:
- receiving means for receiving initial color values for color separation specifications requested by a image processing system;
- error determining means for determining the error between said specified color values and typical luminance values produced by halftoning;
- luminance step determining means for determining the luminance steps for said initial color values which is the difference between said typical luminance values and the value of the next greater halftone levels;
- processing means for processing said luminance errors and said luminance steps to determine adjustment values for said initial color values;
- new color specification means for receiving said adjustment values and said initial color values and for providing new color specifications for said initial color values based on a combination of said adjustment values and said initial color values;
- and
- means for providing said new color specifications to said image processing system wherein said image processing system will render documents displaying reduced luminance false contours within printed documents.
Dependencies are inferred from the claim text.