Method and apparatus indentifying halftone regions within a digital image
First Claim
Patent Images
1. A method for identifying halftone regions, comprising:
- performing by a computer;
receiving a region from a digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values;
computing a variation index for the region, wherein the variation index indicates how frequently adjacent pixel values in the region differ;
in response to determining that the variation index for the region is between an upper threshold and a lower threshold, determining whether the variation index is above a middle threshold and the region contains black patches, wherein the variation index being greater than the upper threshold is indicative of the region being a halftone region and the variation index being less than the lower threshold is indicative of the region being a non-halftone region; and
in response to determining that the variation index is above a middle threshold and that the region contains black patches, determining that the region is a halftone region.
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Abstract
One embodiment of the present invention provides a system that identifies halftone regions within a digital image. During operation, the system receives a region from the digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values. Next, the system computes a variation index for a region of the digital image, wherein the variation index indicates how frequently adjacent pixel values in the region differ. If the variation index for the region is greater than an upper threshold, the system determines that the region is a halftone region.
16 Citations
20 Claims
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1. A method for identifying halftone regions, comprising:
performing by a computer; receiving a region from a digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values; computing a variation index for the region, wherein the variation index indicates how frequently adjacent pixel values in the region differ; in response to determining that the variation index for the region is between an upper threshold and a lower threshold, determining whether the variation index is above a middle threshold and the region contains black patches, wherein the variation index being greater than the upper threshold is indicative of the region being a halftone region and the variation index being less than the lower threshold is indicative of the region being a non-halftone region; and in response to determining that the variation index is above a middle threshold and that the region contains black patches, determining that the region is a halftone region. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform:
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receiving a region from a digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values; computing a variation index for the region, wherein the variation index indicates how frequently adjacent pixel values in the region differ; and if the variation index for the region is greater than an upper threshold, determining that the region is a halftone region; otherwise, if the variation index is lower than the upper threshold; testing to determine if black patches exist in the region; and if black patches exist and the variation index for the region is above a lower threshold and a middle threshold, determining that the region is halftone. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. An apparatus that identifies halftone regions within a digital image, comprising:
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a receiving mechanism configured to receive a region from the digital image, wherein the digital image is a bi-level image, wherein each pixel has two possible color values; an index-computing mechanism configured to compute a variation index for the region of the digital image, wherein the variation index indicates how frequently adjacent pixel values in the region differ; and an identification mechanism, wherein if the variation index for the region is greater than an upper threshold, the identification mechanism is configured to determine that the region is a halftone region;
otherwise, if the variation index is lower than the upper threshold the identification mechanism is configured to determine if black patches exist in the region, and if black patches exist and the variation index for the region is above a lower threshold and above a middle threshold, determine that the region is halftone. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification