System and method for the generation of multiple angle correlation-based digital watermarks
First Claim
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1. A method creating digital watermarks in grayscale images, comprising:
- receiving the first image to be watermarked;
determining the first watermark to be embedded in the first image;
embedding the first watermark into the first image by halftoning the first image using a three-dimensional threshold array having a phase shift value as an input and a first halftone structure defined by the spatial vectors Va1(xa1, ya1) and Vb1(xb1, yb1);
outputting a first watermarked grayscale image containing the first digital watermark embedded with the first halftone structure;
receiving the second image to be watermarked;
determining the second watermark to be embedded in the second image;
embedding the second watermark into the second image by halftoning the second image with a three-dimensional threshold array having a phase shift value as an input and a second halftone structure defined by the spatial vectors Va2(xa2, ya2) and Vb2(xb2, yb2), wherein the interior angle between the two vectors Va1(xa1, ya1) and Vb1(xb1, yb1) of the first halftone structure is equal to the interior angle between the two vectors Va2(xa2, ya2) and Vb2(xb2, yb2) of the second halftone structure, the vector amplitude |Va1(xa1, ya1)| of the first vector of the first halftone structure is equal to the vector amplitude |Va2(xa2, ya2)| of the first vector of the second halftone structure, and the vector amplitude |Vb1(xb1, yb1)| of the second vector of the first halftone structure is equal to the vector amplitude |Vb2(xa2, yb2)| of the second vector of the second halftone structure; and
outputting a second watermarked grayscale image containing the second watermark embedded with the second halftone structure.
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Abstract
Disclosed are systems and methods directed to the generation of digitally watermarked grayscale images having a watermark embedded at different arbitrary Rotation Angles. A single public key can be used to retrieve the otherwise invisible watermarks from the watermarked images when overlaid atop the images at Orientation Angles corresponding to the Rotation Angles.
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Citations
19 Claims
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1. A method creating digital watermarks in grayscale images, comprising:
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receiving the first image to be watermarked; determining the first watermark to be embedded in the first image; embedding the first watermark into the first image by halftoning the first image using a three-dimensional threshold array having a phase shift value as an input and a first halftone structure defined by the spatial vectors Va1(xa1, ya1) and Vb1(xb1, yb1); outputting a first watermarked grayscale image containing the first digital watermark embedded with the first halftone structure; receiving the second image to be watermarked; determining the second watermark to be embedded in the second image; embedding the second watermark into the second image by halftoning the second image with a three-dimensional threshold array having a phase shift value as an input and a second halftone structure defined by the spatial vectors Va2(xa2, ya2) and Vb2(xb2, yb2), wherein the interior angle between the two vectors Va1(xa1, ya1) and Vb1(xb1, yb1) of the first halftone structure is equal to the interior angle between the two vectors Va2(xa2, ya2) and Vb2(xb2, yb2) of the second halftone structure, the vector amplitude |Va1(xa1, ya1)| of the first vector of the first halftone structure is equal to the vector amplitude |Va2(xa2, ya2)| of the first vector of the second halftone structure, and the vector amplitude |Vb1(xb1, yb1)| of the second vector of the first halftone structure is equal to the vector amplitude |Vb2(xa2, yb2)| of the second vector of the second halftone structure; and outputting a second watermarked grayscale image containing the second watermark embedded with the second halftone structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of creating a plurality of grayscale images each having a retrievable invisible digital watermark comprising:
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receiving the grayscale image to be watermarked; determining the grayscale watermark to be embedded in the image; and creating a plurality of digital watermarked grayscale images by embedding a digital watermark into the image by halftoning the image with different halftone structures each defined by the spatial vectors Va(xa, ya) and Vb(xb, yb) having the same interior angle α
, the same vector amplitudes |Va(xa, ya)| and |Va(xa, ya)|, and a different Rotation Angle, wherein the watermark can be retrieved from the plurality of images using a single public key. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A system for digital watermarking of an image, comprising:
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an input image source; image memory for storing the input image to be watermarked; watermark memory for storing the watermark to be embedded in the image; and an image processor including a three-dimensional threshold array where at least one input thereto is a phase shift value for embedding an invisible digital watermark into the image by halftoning the image with the three-dimensional threshold array using a plurality of halftone structures each defined by the spatial vectors Va(xa, ya) and Vb(xb, yb) having the same interior angle α
, the same vector amplitudes |Va(xa, ya)| and |Va(xa, ya)|, and a different Rotation Angle to produce a plurality of digitally watermarked output images.
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17. A method for retrieving a watermark image from a plurality of digitally watermarked grayscale images, each formed by halftoning an image with a halftone structure having a different arbitrary Rotation Angle comprising:
overlaying a single public key transparency having halftone frequencies and angles matching the halftone structure used for forming the plurality of digital watermarked grayscale images atop each of the watermarked images and orienting the key with respect to the watermarked images at Orientation Angles matching the Rotation Angles used for embedding the watermark image into the corresponding digitally watermarked images to retrieve the watermark image. - View Dependent Claims (18, 19)
Specification