Angle avoidance for color halftone screens
AssigneeXerox Corporation
InventorsShen-ge Wang, Beilei Xu, Robert Loce
Life of this patent
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Abstract
A method for avoiding objectionable moiré in a color image can include identifying a problematic excitation angle associated with a problematic excitation in a marking process or in the color image and selecting a set of at least two halftone screens for rendering at least two separations of the color image wherein the set of screens is selected to avoid including significant screen fundamental, harmonic and beat frequencies at angles closer than about 1 degree of the identified problematic excitation angle. Halftoning the color image according to the selected set of screens avoids objectionable moiré associated with the problematic excitation.
Claims23
a method for avoiding objectionable moiré in a color image, the:
- method comprising:
- identifying a problematic excitation angle associated with a problematic excitation in a marking process or in the color image;
- selecting a set of at least two halftone screens for rendering at least two separations of the color image wherein the set of screens is selected to avoid including significant screen fundamental, harmonic and beat frequencies at angles closer than about 1 degree of the identified problematic excitation angle;
- and
- halftoning the color image according to the selected set of screens.
A method for selecting a set of halftone screens for halftoning a color image, the method comprising:
- identifying a problematic excitation in a marking process or in the color image;
- identifying an available pixel grid to be used to render the image;
- identifying screens that are compatible with the available pixel grid;
- selecting at least two candidate screens from the identified screens;
- determining selected respective vector sums of respective combinations of fundamental and/or harmonic frequency components, of the selected at least two candidate screens;
- determining if respective angles of the respective vector sums are separated by at least about one degree from the problematic excitation angle;
- and
- selecting the set of candidate screens if respective angles of the respective vector sums are separated by at least about one degree from the problematic excitation angle.
The method of claim 13 wherein selecting at least one non-orthogonal screen comprises:
- selecting at least two non-orthogonal screens that are each within about eight degrees of orthogonal.
A set of halftone screens for avoiding objectionable moiré when used in conjunction with a problematic excitation, the set of halftone screens comprising:
- a first screen having respective first screen fundamental frequencies, respective first screen harmonics and respective first screen angles associated with the respective first screen fundamental frequencies and harmonics;
- and
- a second screen having respective second screen fundamental frequencies, respective second screen harmonics and respective second screen angles associated with the respective second screen fundamental frequencies and harmonics, wherein the respective first and second screen angles are separated from an angle of the problematic excitation by at least about 1 degree, and wherein angles of beats, between any of the first and second screen fundamentals and harmonics that would otherwise beat with the problematic excitation at visually objectionable frequencies, are separated from the angle of the problematic excitation by at least about 1 degree.
A color image processing system, the system comprising:
- a set of halftone screens including a first screen having respective first screen fundamental frequencies, respective first screen harmonics and respective first screen fundamental and harmonic angles associated with the respective first screen fundamental frequencies and harmonics and a second screen having respective second screen fundamental frequencies, respective second screen harmonics and respective second screen fundamental and harmonic angles associated with the respective second screen fundamental frequencies and harmonics, wherein the respective first and second screen fundamental and harmonic angles are separated from an angle of a problematic excitation by at least about 1 degree, and wherein angles of beats between any of the first and second screen fundamentals and harmonics that would otherwise beat with the problematic excitation in a visually objectionable manner, are separated from the angle of the problematic excitation by at least about 1 degree;
- and
- a halftoner that is operative to prepare the color image for rendering by a rendering device by using the set of halftone screens to halftone the image.
Dependencies are inferred from the claim text.