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System and method of retrieving a watermark within a signal

  • US 7,529,941 B1
  • Filed: 09/12/2006
  • Issued: 05/05/2009
  • Est. Priority Date: 06/04/2001
  • Status: Expired due to Term
First Claim
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1. A computing device for retrieving a watermark in a watermarked signal, the watermarked signal comprising odd and even overlapped blocks where the watermark is contained in even blocks, the computing device comprising:

  • a processor;

    a module configured to control the processor to subtract odd blocks from a k-th block of the watermarked signal to generate a first signal;

    a module configured to control the processor to apply a Fast Fourier Transform (FFT) to the first signal to generate a phase Sk(f);

    a module configured to control the processor to calculate a phase of Sk(f) as φ

    (f) and a phase of an original signal Sk(f) as φ

    (f);

    a module configured to control the processor to calculate the difference Ψ

    (f) between φ

    (f) and φ

    (f); and

    a module configured to control the processor to use a Viterbi search to retrieve the watermark embedded in Ψ

    (f), wherein if during a phase-modulation stage of generating the watermarked signal, the result of adding a phase-modulation to the phase of the original signal has an absolute value greater than π

    , then the computing device further;

    unwraps Ψ

    (f) to obtain a correct phase modulation {tilde over (Φ

    )}k(f) only when φ

    (f)>

    π

    /2 and Ψ

    (f) is greater than a dynamic range of the phase modulation; and

    uses the Viterbi search to retrieve the watermark embedded in {tilde over (Φ

    )}k(f).

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