US6252971B1
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Digital watermarking using phase-shifted stoclustic screens
Assignee: Xerox Corp
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Filing: 1998-04-29
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Granted: 2001-06-26
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Expires: 2018-04-29
Abstract
Abstract A system and method for digital watermark embedding and retrieval using phase shift stoclustic (stochastically clustered) screens. Watermarks are embedded based on the phase shift of clustered halftone screens. Therefore, the hidden information, or invisible watermark, can be detected and visualized by correlating clusters as opposed to the pixel-based correlation required by other methods. Therefore, the detection of watermarks is much easier, especially when distortions have been introduced into the embedded image. By replacing regular cluster halftone screens with stoclustic screens for hidden watermarks, watermarks can quickly be embedded and retrieved
Inventors
- 👤 Shen-ge Wang
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 11:06
CPC Classifications
G; G06; G06T; G06T1/00; G06T1/0021; H; H04; H04N; H04N1/00; H04N1/32; H04N1/32101; H04N1/32144; H04N1/32149; H04N1/32203; H04N1/32256; H04N2201/00; H04N2201/32; H04N2201/3201; H04N2201/3225; H04N2201/3233; H04N2201/3269; H04N2201/327
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
88 words
A method for embedding an invisible digital watermark in an image using phase-shifted stochastically clustered screens, comprising: inputting an image to be embedded with a watermark; determining the watermark to be embedded; establishing cluster centers in the input image; embedding a phase-shifted cluster containing the watermark into the input image, wherein a size of the phase-shifted cluster is modulated according to a desired phase-shift; repeating the determining, establishing and embedding steps until all water marks have been embedded; and outputting the image containing the embedded invisible digital watermark.
Claim 2
Independent Claim
88 words
A method for embedding an invisible digital watermark in an image using phase-shifted stochastically clustered screens, comprising: inputting an image to be embedded with a watermark; determining the watermark to be embedded; establishing cluster centers in the input image; embedding a phase-shifted cluster containing the watermark into the input image, wherein a size of the phase-shifted cluster is modulated according to a desired phase-shift; repeating the determining, establishing and embedding steps until all water marks have been embedded; and outputting the image containing the embedded invisible digital watermark.
Claim 3
Dependent Claim
19 words
The method of claim 1 , wherein establishing cluster centers comprises stochastically locating cluster centers throughout the input image.
Claim 4
Dependent Claim
21 words
The method of claim 1 , wherein the embedding the phase-shifted cluster comprises importing the phase-shifted cluster into the input image.
Claim 5
Dependent Claim
51 words
The method of claim 1 , wherein embedding a phase-shifted cluster comprises importing a sequence of tiles, the tiles comprising the phase-shifted cluster and corresponding to the desired watermark, the sequence of tiles shifting the phase-shifted cluster from zero phase shift to π phase shift and back to zero phase shift.
Claim 6
Dependent Claim
49 words
The method of claim 4 , wherein the tiles determining the phase shift in the cluster are governed by: Δ P i =K ·sin 2 (π· i/N ) where: N is the number of periods; ΔP i is the pitch difference; and i=0, 1, . . . , N−1.
Claim 7
Dependent Claim
32 words
The method of claim 5 , wherein the coefficient K is determined by: ΣΔ P i =P /2, where P denotes the regular pitch, and the summation is taken over N periods.
Claim 8
Dependent Claim
22 words
The method of claim 1 , wherein embedding the phase-shifted cluster comprises embedding the phase-shifted cluster based on a modified halftone process.
Claim 9
Independent Claim
52 words
A system for embedding digital watermarks comprising: an image input device; a watermark embedding device using phase-shifted stochastically clustered (stoclustic) screens, wherein a size of a portion of the stoclustic screens is modulated according to a desired phase-shift, comprising: A watermark circuit, and A watermark character storage device; and An output device.
Claim 10
Independent Claim
52 words
A system for embedding digital watermarks comprising: an image input device; a watermark embedding device using phase-shifted stochastically clustered (stoclustic) screens, wherein a size of a portion of the stoclustic screens is modulated according to a desired phase-shift, comprising: A watermark circuit, and A watermark character storage device; and An output device.
Claim 11
Dependent Claim
31 words
The system of claim 8 , wherein the watermarker circuit embeds the phase-shifted stoclustic screens and comprises: a cluster center locator; a tile pattern importer; and an embedded watermark image generator.
Claim 12
Dependent Claim
19 words
The system of claim 9 , wherein the cluster center locator stochastically locates cluster centers throughout the input image.
Claim 13
Dependent Claim
16 words
The system of claim 9 , wherein the tile pattern importer imports predefined phase-shifted stoclustic screens.
Claim 14
Dependent Claim
49 words
The system of claim 8 , wherein the watermark character storage device stores predefined watermarks in the form of phase-shifted stoclustic screens and contains a set of predefined tiles which accomplish the cluster phase shift from zero phase shift to π phase shift and back to zero phase shift.
Claim 15
Dependent Claim
13 words
The system of claim 8 , further comprising a controller and a memory.
Claim 16
Independent Claim
83 words
A method for retrieving an embedded invisible digital watermark in an image comprising: inputting an image from which the watermark is to be retrieved; estimating a halftone for the input image; generating a phase-shifted stochastically clustered stoclustic reference pattern based on the estimated halftone, wherein a size of a portion of the stoclustic reference pattern is modulated according to a desired phase-shift; overlapping the reference pattern and the input image; visualizing the watermark; and outputting the image containing the now visible digital watermark.
Claim 17
Independent Claim
83 words
A method for retrieving an embedded invisible digital watermark in an image comprising: inputting an image from which the watermark is to be retrieved; estimating a halftone for the input image; generating a phase-shifted stochastically clustered stoclustic reference pattern based on the estimated halftone, wherein a size of a portion of the stoclustic reference pattern is modulated according to a desired phase-shift; overlapping the reference pattern and the input image; visualizing the watermark; and outputting the image containing the now visible digital watermark.
Claim 18
Dependent Claim
25 words
The method of claim 14 , wherein estimating the halftone comprises estimating an average amplitude and an angle of a halftone frequency of the halftone.
Claim 19
Dependent Claim
19 words
The method of claim 15 , wherein estimating the halftone comprises applying a Fast Fourier Transform to the image.
Claim 20
Dependent Claim
21 words
The method of claim 14 , wherein generating the reference pattern comprises using the estimated halftone to generate a reference pattern.
Claim 21
Dependent Claim
26 words
The method of claim 17 , wherein the reference pattern comprises a checkerboard having the same halftone frequency and the same size as the input image.
Claim 22
Independent Claim
51 words
A system for retrieving digital watermarks comprising: an image input device; a watermark extraction device using phase-shifted stochastically clustered (stoclustic) screens, wherein a size of a portion of the stoclustic screens is modulated according to a desired phase-shift, comprising: A halftone pattern generator, and A watermark visualizer; and An output device.
Claim 23
Independent Claim
51 words
A system for retrieving digital watermarks comprising: an image input device; a watermark extraction device using phase-shifted stochastically clustered (stoclustic) screens, wherein a size of a portion of the stoclustic screens is modulated according to a desired phase-shift, comprising: A halftone pattern generator, and A watermark visualizer; and An output device.
Claim 24
Dependent Claim
24 words
The system of claim 19 , wherein the halftone estimator estimates an average amplitude and an angle of a halftone in the input image.
Claim 25
Dependent Claim
29 words
The system of claim 19 , wherein the reference pattern generator generates a reference pattern comprising a checkerboard having the same halftone frequency and size of the input image.
Claim 26
Dependent Claim
24 words
The system of claim 19 , wherein the watermark visualizer further comprises an image overlapper that overlapps the input image and the reference pattern.
Claim 27
Dependent Claim
13 words
The system of claim 19 , further comprising a controller and a memory.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2004-06-25 | 2004-12-25 | 2005-06-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2008-06-25 | 2008-12-25 | 2009-06-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2012-06-25 | 2012-12-25 | 2013-06-26 | $7700.00 | Window Closed / Lapsed |