Automatic adjustment of image watermark strength based on computed image texture
First Claim
1. A method of determining a watermark strength of a watermarked image, the watermarked image formed from an image and a watermark, the watermark strength corresponding to a reference watermark strength of a reference image and the reference image having a set of parameters associated with a measured texture value of the reference image, the method comprising the steps of:
- a) changing the reference watermark strength until a human observer indicates that the watermark is visible;
b) measuring a texture value of at least a portion of the image; and
c) calculating the watermark strength for the watermarked image based on the measured texture value of the image and the set of parameters of the reference image.
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Accused Products
Abstract
A system and method of automatically adjusts watermark strength of a watermarked image based on the content of the image. The described system includes a process by which the correct watermark strength is estimated with a model of preferred watermark strength based upon human perception as measured with a test group. Preferred watermark strength of a watermark within a watermarked reference image is determined and parameter constants associated with measured image texture values for the reference image are then determined. Image texture values are measured for a particular image to be watermarked, and these determined parameter constants are used to predict the strength of the watermark for the particular image. Images are watermarked by modifying the luminance of those pixels that fall within a mask specifying the watermark design. In this way, the chromaticity of the pixel remains constant but the luminance changes. The amount by which the luminance is changed is dependent on the desired strength of the watermark: a stronger watermark demands a larger change in the luminance.
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Citations
17 Claims
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1. A method of determining a watermark strength of a watermarked image, the watermarked image formed from an image and a watermark, the watermark strength corresponding to a reference watermark strength of a reference image and the reference image having a set of parameters associated with a measured texture value of the reference image, the method comprising the steps of:
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a) changing the reference watermark strength until a human observer indicates that the watermark is visible;
b) measuring a texture value of at least a portion of the image; and
c) calculating the watermark strength for the watermarked image based on the measured texture value of the image and the set of parameters of the reference image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for setting a watermark strength of a watermark within a watermarked image, the watermarked image formed from an image and the watermark, the watermark strength corresponding to a reference watermark strength of a reference image and having a set of parameters associated with a measured texture value of the reference image, comprising:
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receiving means for receiving from at least one human subject, an indication that the watermark is visible in said reference image which corresponds to said image;
measuring means for measuring a texture value of at least a portion of the image;
calculating means for calculating the watermark strength for the watermarked image based on the measured texture value of the image and the set of parameters of the reference image; and
adjusting means for adjusting a current strength of at least one portion of the watermarked image so as to provide the strength level for the watermarked image. - View Dependent Claims (11, 12, 13)
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14. Apparatus for watermarking a plurality of images, each watermarked one of the plurality of images having a watermark strength, the apparatus comprising:
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receiving means for receiving from at least one human subject, an indication that the watermark is visible in a reference image which corresponds to said image;
storage means for storing a plurality of watermarks and for storing a plurality of sets of parameters, each of the sets of parameters associated with at least one measured texture value of said reference image; and
processing means for processing a received one of the plurality of images with a selected one of the plurality of watermarks, the processing means including;
measuring means for measuring at least one texture value of at least a portion of the received one of the plurality of images;
selecting means for selecting one set of the plurality of sets of parameters based on the selected one of the plurality of watermarks and the received one of the plurality of images;
calculating means for calculating the watermark strength based on the at least one measured texture value and the selected set of the plurality of sets of parameters;
watermarking means for applying the selected one of the plurality of watermarks to the received one of the plurality of images to obtain a watermarked image having a current strength; and
adjusting means for adjusting the current strength level of the watermarked image to the calculated watermark strength to provide the one watermarked image. - View Dependent Claims (15)
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16. A method of determining a watermark strength of a watermarked source image, the watermarked source image formed from a source image and a watermark, the watermark strength based on the source image and a reference watermark strength of a reference image and the reference image having a set of parameters associated with a measured texture value of the reference image, the method comprising the steps of:
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a) selecting an image for use as a reference image;
b) determining the reference watermark strength by adjusting the strength of the watermark applied to said reference image until a human observer indicates that the watermark has been seen;
c) measuring the texture of said reference image; and
developing a set of parameters of the reference image that describe the texture for said reference image;
d) measuring a texture value of at least a portion of the source image; and
e) calculating the watermark strength for the watermarked image based on the measured texture value of the source image, the reference watermark strength, and the set of parameters of the reference image.
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17. A method of determining a watermark strength of a watermarked source image, the watermarked source image formed from a source image and a watermark, the watermark strength based on the source image and a reference watermark strength of a reference image and a set of parameters associated with a measured texture value of said reference image, the method comprising the steps of:
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a) selecting a set of prototype images;
b) for each of the prototype images;
determining a just-visible watermark strength by adjusting the strength of the watermark applied to said prototype image until a human observer indicates that the watermark has been seen; and
measuring the texture of said prototype image and developing a set of parameters that describe the texture for said prototype image;
c) selecting one of the prototype images as a reference image wherein the reference watermark strength is the just-visible strength of the selected prototype image and the set of reference parameters is the set of parameters describing the texture of said selected prototype image;
d) measuring a texture value of at least a portion of the source image; and
e) calculating the watermark strength for the watermarked image based on the measured texture value of the source image, the reference watermark strength, and the set of parameters of the reference image.
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Specification