Patent US6694041B1 successfully refreshed from Google Patents.
US6694041B1
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Halftone watermarking and related applications
Assignee: Digimarc Corp
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Filing: 2000-10-11
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Granted: 2004-02-17
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Expires: 2020-10-11
Abstract
Abstract One method for halftone image watermarking assigns halftone watermark dot values to pseudorandom locations in an image and diffuses the error of the watermark to neighboring pixel locations of these dots. This method may be used in conjunction with a robust watermark spread throughout image before embedding the halftone watermark. The robust watermark carries a key used to decode the halftone watermark. Another method for halftone image watermarking computes a watermark image at the resolution of a halftone image. The method modulates the halftone image with the watermark image.
Inventors
- 👤 Hugh L. Brunk
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 12:30
CPC Classifications
G; G06; G06T; G06T1/00; G06T1/0021; G06T1/005; G06T1/0071; H; H04; H04N; H04N17/00; H04N17/004; H04N21/00; H04N21/40; H04N21/43; H04N21/442; H04N21/4425; H04N21/80; H04N21/83; H04N21/835; H04N21/8358; G06T2201/00; G06T2201/005; G06T2201/0051
Claims Analysis
Total Claims: 40
Claim 1
Independent Claim
102 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein error associated with the halftone watermark values is diffused in one direction in the image, and error associated with converting multilevel pixel values in the image to a halftone image is diffused in another direction.
Claim 2
Independent Claim
102 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein error associated with the halftone watermark values is diffused in one direction in the image, and error associated with converting multilevel pixel values in the image to a halftone image is diffused in another direction.
Claim 3
Dependent Claim
17 words
A computer readable medium on which is stored software for performing the method of claim 1 .
Claim 4
Independent Claim
80 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein the locations and values of halftone watermark dots are specified by a key.
Claim 5
Independent Claim
80 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein the locations and values of halftone watermark dots are specified by a key.
Claim 6
Dependent Claim
18 words
The method of claim 3 wherein the key is carried in a separate watermark embedded in the image.
Claim 7
Dependent Claim
25 words
The method of claim 3 wherein the key is used to seed a pseudorandom process that specifies the values and locations of the halftone watermark.
Claim 8
Independent Claim
85 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; embedding a watermark into a multilevel pixel representation of an image before converting the image to the halftone image.
Claim 9
Independent Claim
85 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; embedding a watermark into a multilevel pixel representation of an image before converting the image to the halftone image.
Claim 10
Dependent Claim
34 words
The method of claim 6 wherein the watermark embedded in the multilevel pixel representation of the image includes a watermark orientation signal used to detect the watermark in an image after undergoing geometric distortion.
Claim 11
Dependent Claim
25 words
The method of claim 6 wherein the watermark in the multilevel pixel representation carries a message including a key specifying locations of the halftone watermark.
Claim 12
Independent Claim
55 words
A method of decoding a halftone watermark from an image comprising: deriving a key from data embedded in the image; using the key to identify locations and values of a halftone watermark; and analyzing pixel values at the locations to determine whether the values at the locations correspond to the values specified by the key.
Claim 13
Independent Claim
55 words
A method of decoding a halftone watermark from an image comprising: deriving a key from data embedded in the image; using the key to identify locations and values of a halftone watermark; and analyzing pixel values at the locations to determine whether the values at the locations correspond to the values specified by the key.
Claim 14
Dependent Claim
40 words
The method of claim 9 including: scanning a printed version of the image at a suitably high resolution to read halftone watermark dots embedded into the printed version of the image; and then performing the actions of claim 9 .
Claim 15
Dependent Claim
17 words
The method of claim 9 wherein the key is derived from a watermark embedded in the image.
Claim 16
Dependent Claim
23 words
The method of claim 11 wherein the watermark from which the key is derived is embedded so as to survive printing and scanning.
Claim 17
Dependent Claim
40 words
The method of claim 11 including: detecting an orientation signal and using the orientation signal to determined orientation parameters of the watermark; and using the orientation parameters to read a message embedded in the watermark, the message including the key.
Claim 18
Dependent Claim
14 words
A computer readable medium having software for performing the method of claim 9 .
Claim 19
Independent Claim
75 words
A method of embedding a watermark in a halftone image comprising: computing a watermark image comprising an array of values corresponding to pixel locations in a halftone image; embedding the watermark image in the halftone image by using the values of the watermark image to modulate thresholds at the pixel locations, where the thresholds are used to convert multilevel pixel values in a multilevel per pixel image into halftone pixel values of the halftone image.
Claim 20
Independent Claim
75 words
A method of embedding a watermark in a halftone image comprising: computing a watermark image comprising an array of values corresponding to pixel locations in a halftone image; embedding the watermark image in the halftone image by using the values of the watermark image to modulate thresholds at the pixel locations, where the thresholds are used to convert multilevel pixel values in a multilevel per pixel image into halftone pixel values of the halftone image.
Claim 21
Dependent Claim
25 words
The method of claim 15 wherein the watermark image comprises an orientation watermark signal enabling a watermark decoder to compensate for rotation, scale and translation.
Claim 22
Dependent Claim
22 words
The method of claim 15 wherein the watermark image comprises a watermark message signal carrying a message of two or more symbols.
Claim 23
Dependent Claim
17 words
A computer readable medium on which is stored software for performing the method of claim 15 .
Claim 24
Independent Claim
86 words
A method of embedding a watermark in a halftone image comprising: computing a watermark image comprising an array of values corresponding to pixel locations in a target halftone image at a resolution; combining the array of values of the watermark image with corresponding multilevel pixel values of a multilevel per pixel image to create a watermarked multilevel per pixel image at the resolution of the target halftone image; and performing a halftone process to convert the watermarked multilevel per pixel image to a watermarked halftone image.
Claim 25
Independent Claim
86 words
A method of embedding a watermark in a halftone image comprising: computing a watermark image comprising an array of values corresponding to pixel locations in a target halftone image at a resolution; combining the array of values of the watermark image with corresponding multilevel pixel values of a multilevel per pixel image to create a watermarked multilevel per pixel image at the resolution of the target halftone image; and performing a halftone process to convert the watermarked multilevel per pixel image to a watermarked halftone image.
Claim 26
Dependent Claim
28 words
The method of claim 19 wherein combining comprises adding the array of values of the watermark image with the corresponding pixel values of the multilevel per pixel image.
Claim 27
Dependent Claim
23 words
The method of claim 19 wherein performing the halftone process includes performing an error diffusion process on the watermarked multilevel per pixel image.
Claim 28
Dependent Claim
23 words
The method of claim 19 wherein performing the halftone process includes performing an ordered dithering process on the watermarked multilevel per pixel image.
Claim 29
Dependent Claim
25 words
The method of claim 19 wherein the watermark image comprises an orientation watermark signal enabling a watermark decoder to compensate for rotation, scale and translation.
Claim 30
Dependent Claim
22 words
The method of claim 19 wherein the watermark image comprises a watermark message signal carrying a message of two or more symbols.
Claim 31
Dependent Claim
17 words
A computer readable medium on which is stored software for performing the method of claim 19 .
Claim 32
Dependent Claim
124 words
A watermark decoder comprising: a watermark detector for analyzing portions of an image to detect a watermark signal embedded in the image, the image having been scanned from a halftone printed image at a sufficiently high resolution to discern a watermark image embedded at a resolution of the halftone image; and a watermark reader for reading a watermark signal from the portions of the image; wherein the decoder is operable to use a key to identify locations and values of a halftone watermark, and is operable to detect alteration of the image by analyzing pixel values at the locations to determine whether the values at the locations correspond to the values specified by the key; and wherein the key is derived from the image.
Claim 33
Dependent Claim
124 words
A watermark decoder comprising: a watermark detector for analyzing portions of an image to detect a watermark signal embedded in the image, the image having been scanned from a halftone printed image at a sufficiently high resolution to discern a watermark image embedded at a resolution of the halftone image; and a watermark reader for reading a watermark signal from the portions of the image; wherein the decoder is operable to use a key to identify locations and values of a halftone watermark, and is operable to detect alteration of the image by analyzing pixel values at the locations to determine whether the values at the locations correspond to the values specified by the key; and wherein the key is derived from the image.
Claim 34
Dependent Claim
29 words
The watermark decoder of claim 26 wherein the key is decoded from a primary watermark in the image and the halftone watermark is a secondary watermark in the image.
Claim 35
Dependent Claim
78 words
The watermark decoder of claim 26 wherein the watermark signal is encoded by computing a watermark image comprising an array of values corresponding to pixel locations in a halftone image, and embedding the watermark image in the halftone image by using the values of the watermark image to modulate thresholds at the pixel locations, where the thresholds are used to convert multilevel pixel values in a multilevel per pixel image into halftone pixel values of the halftone image.
Claim 36
Dependent Claim
22 words
The method of claim 28 wherein the watermark decoder is operable to detect alteration of the image by analyzing the watermark signal.
Claim 37
Dependent Claim
88 words
The watermark decoder of claim 26 wherein the watermark signal is encoded by computing a watermark image comprising an array of values corresponding to pixel locations in a target halftone image at a resolution, combining the array of values of the watermark image with corresponding multilevel pixel values of a multilevel per pixel image to create a watermarked multilevel per pixel image at the resolution of the target halftone image, and performing a halftone process to convert the watermarked multilevel per pixel image to a watermarked halftone image.
Claim 38
Dependent Claim
23 words
The watermark decoder of claim 30 wherein the watermark decoder is operable to detect alteration of the image by analyzing the watermark signal.
Claim 39
Independent Claim
82 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein values and locations of the halftone watermark are chosen using a human visual system model.
Claim 40
Independent Claim
82 words
A method of halftone image watermarking comprising: assigning a set of halftone watermark values to locations within a halftone image; and diffusing error associated with the halftone watermark values to neighboring locations within the halftone image, where the error is characterized as a difference between multilevel pixel value at a location of a halftone watermark dot, and the halftone watermark value of the halftone watermark dot; wherein values and locations of the halftone watermark are chosen using a human visual system model.
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