Digital watermark detection method and apparatus
First Claim
1. A digital watermark detection apparatus to detect watermark information embedded in an input image signal, comprising:
- an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and
a detector to detect the watermark information in the size-reduced image signal, the detector including;
a correlator to compute an auto-correlation function of the size-reduced image signal;
an extraction unit configured to extract a specific frequency component signal by filtering the auto-correlation function; and
an estimation unit configured to estimate the watermark information from the specific frequency component signal,wherein the correlator includes a controller which controls a phase of the size-reduced image signal to generate a phase-controlled image signal, the correlator computing, as the auto-correlation function, a correlation value between the phase-controlled image signal and the size-reduced image signal.
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Abstract
An image size reduction unit reduces the image size of an input image signal, thereby generating a size-reduced image signal. A specific frequency component extraction unit extracts a specific frequency component signal from the size-reduced image signal. A phase controller controls the phase of the specific frequency component signal. A correlator computes a cross-correlation value between the phase-controlled specific frequency component signal and size-reduced image signal. A watermark information estimation unit estimates, from the cross-correlation value, watermark information embedded in the input image signal.
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Citations
7 Claims
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1. A digital watermark detection apparatus to detect watermark information embedded in an input image signal, comprising:
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an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and a detector to detect the watermark information in the size-reduced image signal, the detector including; a correlator to compute an auto-correlation function of the size-reduced image signal; an extraction unit configured to extract a specific frequency component signal by filtering the auto-correlation function; and an estimation unit configured to estimate the watermark information from the specific frequency component signal, wherein the correlator includes a controller which controls a phase of the size-reduced image signal to generate a phase-controlled image signal, the correlator computing, as the auto-correlation function, a correlation value between the phase-controlled image signal and the size-reduced image signal.
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2. A digital watermark detection apparatus to detect watermark information embedded in an input image signal, comprising:
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an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and a detector to detect the watermark information in the size-reduced image signal, the detector including; a correlator to compute an auto-correlation function of the size-reduced image signal; an extraction unit configured to extract a specific frequency component signal by filtering the auto-correlation function; and an estimation unit configured to estimate the watermark information from the specific frequency component signal, wherein the estimation unit estimates the watermark information by determining a polarity of a peak of the specific frequency component signal.
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3. A digital watermark detection apparatus to detect watermark information embedded in an input image signal, comprising:
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an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and a detector to detect the watermark information in the size-reduced image signal, the detector including; a correlator which computes an auto-correlation function of the size-reduced image signal; a first accumulator which accumulates the auto-correlation function for a first period of time to generate a first accumulation signal; an extraction unit configured to extract a specific frequency component signal from the first accumulation signal; a normalizing unit configured to normalize an amplitude of the specific frequency component signal; a second accumulator which accumulates the normalized specific frequency component signal for a second period of time longer than the first period of time to generate a second accumulation signal; and an estimation unit configured to estimate the watermark information from the second accumulation signal; wherein the correlator includes a controller which controls a phase of the size-reduced image signal to generate a phase-controlled image signal, the correlator computing, as the auto-correlation function, a correlation value between the phase-controlled image signal and the size-reduced image signal.
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4. A digital watermark detection apparatus to detect watermark information embedded in an input image signal, comprising:
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an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and a detector to detect the watermark information in the size-reduced image signal, the detector including; an extraction unit configured to extract a specific frequency component signal from the size-reduced image signal; a phase controller to control a phase of the specific frequency component signal; a correlator to compute a cross-correlation value between the phase-controlled specific frequency component signal and the size-reduced image signal; and an estimation unit configured to estimate the watermark information from the cross-correlation value; and an image rotation unit located before the detector and configured to perform an image rotation operation on the size-reduced image signal. - View Dependent Claims (5, 6)
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7. A digital watermark detection apparatus, to detect watermark information embedded in an input image signal, comprising:
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an image-size-reduction unit configured to reduce an image size of the input image signal by reducing resolution of the input image signal and to generate a size-reduced image signal; and a detector to detect the watermark information in the size-reduced image signal, the detector including; an extraction unit configured to extract a specific frequency component signal from the size-reduced image signal; a phase controller to control a phase of the specific frequency component signal; a correlator to compute a cross-correlation value between the phase-controlled specific frequency component signal and the size-reduced image signal; and an estimation unit configured to estimate the watermark information from the cross-correlation value; wherein the size-reduced image signal has a particular reduction ratio with respect to the input image signal, and the specific frequency component signal has a frequency corresponding to the particular reduction ratio of the size-reduced image signal.
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Specification