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US5799112A
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Method and apparatus for wavelet-based universal halftone image unscreening
Assignee: Xerox Corp
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Filing: 1996-08-30
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Granted: 1998-08-25
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Expires: 2016-08-30
Abstract
Abstract A universal halftone image unscreening method includes: 1) decomposing the halftone image into a plurality of subband image levels, where each subband image level includes a plurality of subband images; 2) selectively filtering the plurality of subband images of each subband image level; and 3) recomposing the plurality of filtered subband images into a continuous tone image. The continuous tone image can then be further filtered to enhance its appearance. The subband images are preferably formed using the discrete wavelet transform, but can be formed using any known transform. The subband images are selectively filtered using a non-edge areas noise attenuating filter and a plurality of oriented filters. The halftone image is preferably decomposed using an N-stage halftone image decomposer, wherein each of the N decomposer stages comprises a set of low-pass and high-pass filters. Similarly, the continuous tone image is preferably recomposed using an N-stage continuous tone image recomposer, wherein each of the N recomposer stages comprises a set of low-pass and high-pass filters. The universal halftone unscreening method and apparatus are able to unscreen any halftone image to form the continuous tone image without needing any information about the halftone image halftoning process, and are able to unscreen both original, electronically stored, halftone image data and printed halftone images which have been scanned to generated the electronic image data.
Inventors
- 👤 Ricardo L. de Queiroz
- 👤 Jiebo Luo
- 👤 Zhigang Fan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 10:43
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/40075
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
50 words
A method for creating a continuous tone image from a halftone image, comprising: decomposing the halftone image into a plurality of subband images; selectively removing at least one of noise and patterns from the plurality of subband images; and recomposing the plurality of subband images into the continuous tone image.
Claim 2
Independent Claim
50 words
A method for creating a continuous tone image from a halftone image, comprising: decomposing the halftone image into a plurality of subband images; selectively removing at least one of noise and patterns from the plurality of subband images; and recomposing the plurality of subband images into the continuous tone image.
Claim 3
Dependent Claim
33 words
The method for creating the continuous tone image from the halftone image of claim 1, further comprising filtering the continuous tone image using an edge-preserving filter to form an enhanced continuous tone image.
Claim 4
Dependent Claim
40 words
The method for creating the continuous tone image from the halftone image of claim 2, wherein the continuous tone image filtering step comprises non-linearly filtering the continuous tone image using spatial smoothness constraints modeled using a Huber Markov random field.
Claim 5
Dependent Claim
23 words
The method for creating the continuous tone image from the halftone image of claim 2, wherein the edge-preserving filter is a non-linear filter.
Claim 6
Dependent Claim
23 words
The method for creating the continuous tone image from the halftone image of claim 4, wherein the edge preserving filter is a σ-filter.
Claim 7
Dependent Claim
39 words
The method for creating the continuous tone image from the halftone image of claim 1, wherein the halftone decomposing step comprises decomposing the halftone image into a plurality of different frequency subband images based on a discrete wavelet transform.
Claim 8
Dependent Claim
72 words
The method for creating the continuous tone image from the halftone image of claim 1, wherein the halftone decomposing step comprises: decomposing the halftone image into a plurality of different first level frequency subband images; decomposing one of the plurality of first level subband images into a plurality of second level different frequency subband images; and repeating the subband image decomposing step for at least the plurality of second level subband images.
Claim 9
Dependent Claim
46 words
The method for creating the continuous tone image from the halftone image of claim 1, wherein the selectively removing step comprises: attenuating noise from non-edge areas of each of the plurality of subband images; and oriented filtering of each of the plurality of noise-attenuated subband images.
Claim 10
Dependent Claim
31 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein the noise-attenuating step comprises clipping the magnitudes of the pixels of high frequency subband images.
Claim 11
Dependent Claim
61 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein the noise-attenuating step comprises: weighting magnitudes of coefficients for a parent subband image for each high frequency subband image; and clipping magnitudes of coefficients of the high frequency subband images to at most the weighted magnitudes of the coefficients of the corresponding parent subband image.
Claim 12
Dependent Claim
33 words
The method for creating the continuous tone image from the halftone image of claim 10, wherein the magnitude weighting step comprises varying the weighing based on a level of the high frequency subband.
Claim 13
Dependent Claim
28 words
The method for creating the continuous tone image from the halftone image of claim 10, wherein the clipping step adapts to edges in the high frequency subband images.
Claim 14
Dependent Claim
33 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein the oriented filtering step comprises applying a one-dimensional low-pass filter along an orientation of each subband image.
Claim 15
Dependent Claim
53 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein oriented filtering step comprises applying one of a plurality of oriented filters to each of the subband images, the plurality of oriented filters comprising a horizontal low-pass filter, a vertical low-pass filter and a X-shaped low-pass filter.
Claim 16
Dependent Claim
49 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein the oriented filtering step comprises: applying a horizontal low-pass filter to vertical subband images; applying a vertical low-pass filter to horizontal subband images; and applying a X-shaped low-pass filter to diagonal subband images.
Claim 17
Dependent Claim
32 words
The method for creating the continuous tone image from the halftone image of claim 8, wherein the oriented filtering step comprises adapting the oriented filtering to a resolution of the subband images.
Claim 18
Dependent Claim
32 words
The method for creating the continuous tone image from the halftone image of claim 16, wherein the oriented filtering step further comprises selecting appropriate filters based on estimates of the screen parameters.
Claim 19
Independent Claim
58 words
An apparatus for converting a halftone image into a continuous tone image, comprising: decomposing means for decomposing the halftone image into a plurality of subband images; means for selectively removing at least one of noise and patterns from the plurality of subband images; and recomposing means for recomposing the plurality of subband images into the continuous tone image.
Claim 20
Independent Claim
58 words
An apparatus for converting a halftone image into a continuous tone image, comprising: decomposing means for decomposing the halftone image into a plurality of subband images; means for selectively removing at least one of noise and patterns from the plurality of subband images; and recomposing means for recomposing the plurality of subband images into the continuous tone image.
Claim 21
Dependent Claim
24 words
The apparatus for converting a halftone image into a continuous tone image of claim 18, further comprising means for filtering the continuous tone image.
Claim 22
Independent Claim
29 words
An apparatus for converting a halftone image into a continuous tone image, comprising: an N-stage halftone image decomposer; a subband noise/pattern filter system; and an N-stage subband image recomposer.
Claim 23
Independent Claim
29 words
An apparatus for converting a halftone image into a continuous tone image, comprising: an N-stage halftone image decomposer; a subband noise/pattern filter system; and an N-stage subband image recomposer.
Claim 24
Dependent Claim
23 words
The apparatus for converting a halftone image into a continuous tone image of claim 20, further comprising a continuous tone image filter system.
Claim 25
Dependent Claim
39 words
The apparatus for converting a halftone image into a continuous tone image of claim 20, wherein the N-stage halftone image decomposer comprises: a halftone image to subband image decomposer; and at least one subband image to subband image decomposer.
Claim 26
Dependent Claim
91 words
The apparatus for converting a halftone image into a continuous tone image of claim 22, wherein the halftone image to subband image decomposer and each at least one subband image to subband image decomposer comprises: a first low-pass filter and a first high-pass filter inputting one of the halftone image and a subband image; a second low-pass filter and a second high-pass filter connected to an output of the first low-pass filter; and a third low-pass filter and a third high-pass filter connected to an output of the first high-pass filter.
Claim 27
Dependent Claim
40 words
The apparatus for converting a halftone image into a continuous tone image of claim 20, wherein the N-stage subband image recomposer comprises: at least one subband image to subband image recomposer; and a subband image to continuous tone image recomposer.
Claim 28
Dependent Claim
140 words
The apparatus for converting a halftone image into a continuous tone image of claim 24, wherein the subband image to continuous tone image recomposer and each at least one subband image to subband image recomposer comprises: a first low-pass filter, a second low-pass filter, a first high-pass filter and a second high-pass filter, each filter inputting a different one of a plurality of subband images of a previous subband image level; a third low-pass filter connected to outputs of each of the first low-pass filter and the first high-pass filter; and a third high-pass filter connected to outputs of each of the second low-pass filter and the second high-pass filter; wherein outputs of the third low-pass and third high-pass filters are combined to form one of a subband image of a current subband image level and the continuous tone image.
Claim 29
Dependent Claim
35 words
The apparatus for converting a halftone image into a continuous tone image of claim 20, wherein the subband noise/pattern filter system comprises: a non-edge area noise attenuating filter; and a subband image oriented filter system.
Claim 30
Dependent Claim
65 words
The apparatus for converting a halftone image into a continuous tone image of claim 26, wherein the subband image oriented filter system comprises: a subband image orientation analyzer; and a plurality of oriented filters; wherein each of the subband images is filtered by one of the plurality of oriented filters based on an orientation of that subband image determined by the subband image orientation analyzer.
Claim 31
Dependent Claim
35 words
The apparatus for converting a halftone image into a continuous tone image of claim 27, wherein the plurality of oriented filters comprises: a horizontal subband filter; a vertical subband filter; and a diagonal subband filter.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2001-08-24 | 2002-02-23 | 2002-08-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2005-08-24 | 2006-02-23 | 2006-08-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2009-08-24 | 2010-02-23 | 2010-08-25 | $7700.00 | Window Closed / Lapsed |