N-color printing with hexagonal rosettes
AssigneeXerox Corporation
InventorsShen-Ge Wang, Robert P Loce
Life of this patent
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Abstract
What is provided herein are systems and methods for digitally reproducing a moiré-free color halftone image using an enhanced halftone screen set consisting of a halftone screen for each of N colorants, where N>4. Also disclosed is an enhanced color halftoning screening apparatus for reproducing a moiré-free color halftone image using an enhanced halftone screen set consisting of a halftone screen for each of N colorants, N>4. Further disclosed are embodiments for generating a plurality of non-orthogonal halftone screen outputs for moiré-free enhanced color halftoning.
Claims25
An image forming method for digitally reproducing a moiré-free color halftone image using an enhanced halftone screen set consisting of a halftone screen for each of N colorants, N>4, the method comprising:
- using a color halftoning screening apparatus to perform:
- defining rosette fundamental frequency vectors (VR1, VR2) that satisfy a length and sum requirement to meet visual acceptability standards according to |VR1|>fmin, |VR2|>fmin, and |VR1±VR2|>fmin;
- defining N halftone screens for colorants i=1, N, respectively possessing first and second frequency vectors (Vi1, Vi2), where no two screens possess identical fundamental frequency vector pairs;
- selecting fundamental frequency vectors for the N halftone screens according to:
- (Vi1, Vi2)=(mi1VR1+mi2VR2, ni1VR1+ni2VR2) for integer m's and n's, where at least one fundamental frequency vector or its conjugate satisfies one of the following:
- Vik=VR1, Vik=VR2, and |Vik|>2max [|VR1|, |VR2|];
- such that the set of N different halftone screens used in combination produces a moiré-free halftone output;
- and
- using said N halftone screens, as further specified by said selected fundamental frequency vectors, in an image forming apparatus for digital reproduction of a moiré-free color halftone image.
A method for generating a plurality of non-orthogonal halftone screen outputs for moiré-free enhanced color halftoning, the method comprising:
- using a color halftoning screening apparatus to perform:
- defining rosette fundamental frequency vectors (VR1, VR2) that satisfy a length and a sum requirement to meet visual acceptability standards according to:
- |VR1|>fmin, |VR2|>fmin, and |VR1±VR2|>fmin;
- and,
- specifying a first and a second color halftone screen fundamental frequency vector for each of N halftone screens, N>4 according to:
- (Vi1, Vi2)=(mi1VR1+mi2VR2, ni1VR1+ni2VR2) for integer m's and n's, where at least one of the fundamental frequency vectors or its conjugate must also occur off of a second-order spectral hexagon which connects frequency components that lie just outside of a first-order spectral hexagon;
- and
- using said N halftone screens, as further specified by said first and second fundamental frequency vectors, in an image forming apparatus for digital reproduction of a moiré-free color halftone image.
A color halftoning screening apparatus for reproducing a moiré-free color halftone image using an enhanced halftone screen set consisting of a halftone screen for each of N colorants, N>4, the apparatus comprising:
- rosette fundamental frequency vectors VR1, VR2 that satisfy a length and sum requirement to meet visual acceptability standards according to |VR1|>fmin, |VR2|>fmin, and |VR1±VR2|>fmin;
- N halftone screens for colorants i=1, N, respectively possessing first and second frequency vectors (Vi1, Vi2), where no two screens possess identical fundamental frequency vector pairs;
- and
- fundamental frequency vectors for the N halftone screens according to (Vi1, Vi2)=(mi1VR1+mi2VR2, ni1VR1+ni2VR2) for integer m's and n's, where at least one fundamental frequency vector or its conjugate also satisfies one of the following:
- Vik=VR1, Vik=VR2, and |Vik|>2max [|VR1|, |VR2|].
Dependencies are inferred from the claim text.