Rehalftoning of gray halftones with optimal screen frequency for robust suppression of moire
First Claim
1. A method of rendering an image based on an original halftone image, the method comprising:
- determining a frequency of a significant frequency component of the original halftone image;
selecting a rehalftone frequency, based on the frequency of the significant frequency component, the selection being directed toward producing moiré
of unobjectionably high frequency;
rehalftoning the original halftone image at the selected rehalftone frequency; and
, rendering the image based on the rehalftoning.
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Accused Products
Abstract
Optimal rehalftone screen frequencies are found by searching frequency space for points that are maximally spaced from significant frequency components of an input image halftone screen or screens. Selecting a rehalftone screen having a maximally spaced frequency produces moiré of the highest frequency possible. High frequency moiré are visually unobjectionable. Optimal rehalftone frequencies may be found near the maximally spaced points where system or other constraints limit the usefulness of the maximally spaced points. Rehalftone screen frequencies in the range of about 1.4 to about 1.8 times the fundamental frequency of the input image halftone screen are often optimal. A rehalftone screen frequency of 1.5 times the fundamental frequency of the input image halftone screen is often optimal when the input image is monochrome and uses a dot screen.
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Citations
25 Claims
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1. A method of rendering an image based on an original halftone image, the method comprising:
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determining a frequency of a significant frequency component of the original halftone image;
selecting a rehalftone frequency, based on the frequency of the significant frequency component, the selection being directed toward producing moiré
of unobjectionably high frequency;
rehalftoning the original halftone image at the selected rehalftone frequency; and
,rendering the image based on the rehalftoning. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of rendering an image based on an original halftone image, the method comprising:
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determining a halftone frequency of the original halftone image;
selecting a rehalftone frequency to be 1.4 to 1.8 or 2.4 to 2.8 times the fundamental frequency of the original halftone image;
rehalftoning the original halftone image at the selected rehalftone frequency; and
,rendering the image based on the rehalftoning, thereby ensuring that no visually objectionable moiré
occur. - View Dependent Claims (12, 13, 14, 15)
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16. A system operative to render an image based on an original halftone image, the system comprising:
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a halftone frequency classifier operative to determine a significant frequency component of the original halftone image;
a screen selector operative to select a rehalftone screen having a rehalftone frequency based on the significant frequency component, the selection being directed toward producing moiré
of unobjectionably high frequency;
a rehalftoner operative to rehalftone an image, based on the original halftone image, with the selected rehalftone screen; and
,a rendering device operative to render the image. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification