Watermark detection
First Claim
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1. A method of detecting a watermark in an information signal, comprising the steps of:
- computing a value indicative of the correlation of said information signal and said watermark; and
detecting whether said correlation value is larger than a predetermined threshold;
characterized in that said computing comprises the steps of Fourier transforming the information signal and the watermark into respective Fourier coefficients, multiplying corresponding coefficients to obtain Fourier coefficients representing correlation values each corresponding with one of a plurality of positions of the watermark with respect to the information signal, and inverse transforming the Fourier coefficients representing the correlation values;
said step of detecting comprises detecting whether at least one of said correlation values is larger than the predetermined threshold;
the method further including the step of normalizing the Fourier coefficients representing the correlation values to substantially the same magnitudes.
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Abstract
An improved method and arrangement for detecting a watermark in an information (e.g. image or video) signal are disclosed. The detection is more reliable and less vulnerable to image processing by subjecting the suspect image (q) and the watermark to be detected (w) to Symmetrical Phase Only Matched Filtering (24-28,16) prior to detecting (29) the amount of correlation (d) between said signals.
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8 Claims
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1. A method of detecting a watermark in an information signal, comprising the steps of:
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computing a value indicative of the correlation of said information signal and said watermark; and
detecting whether said correlation value is larger than a predetermined threshold;
characterized in that said computing comprises the steps of Fourier transforming the information signal and the watermark into respective Fourier coefficients, multiplying corresponding coefficients to obtain Fourier coefficients representing correlation values each corresponding with one of a plurality of positions of the watermark with respect to the information signal, and inverse transforming the Fourier coefficients representing the correlation values;
said step of detecting comprises detecting whether at least one of said correlation values is larger than the predetermined threshold;
the method further including the step of normalizing the Fourier coefficients representing the correlation values to substantially the same magnitudes. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An arrangement for detecting a watermark (w) in an information signal (q), comprising:
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means (24-28) for computing a value (d) indicative of the correlation of said information signal and said watermark; and
means (29) for detecting whether said correlation value is larger than a predetermined threshold;
characterized in that said computing means comprise means (24,25) for Fourier transforming the information signal and the watermark into respective Fourier coefficients, means (27) for multiplying corresponding coefficients to obtain Fourier coefficients representing correlation values each corresponding with one of a plurality of positions of the watermark with respect to the information signal, and means (28) for inverse transforming the Fourier coefficients representing the correlation values;
said detecting means (29) are arranged to detect whether at least one of said correlation values is larger than the predetermined threshold;
the arrangement further including means (30) for normalizing the Fourier coefficients representing the correlation values to substantially the same magnitudes. - View Dependent Claims (8)
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Specification