Patent ID: 7471807

Claim:
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.