Koninklijke Philips Corporation N.v.

Koninklijke Phillips Electronics N.v.

Geert F G Depovere

Antonius A C M Kalker

Jaap Andre Haitsma

Johan P M G Linnartz

Maurice J J J-b Maes

Marten Erik Van Dijk

Peter M J Rongen

Marc J R Op De Beeck

Christianus W F Vriens

An input image is distorted so that it has less correlation to a watermark and the distorted image is subtracted from the input image to provide a preprocessed image. If the correlation between the preprocessed image and a watermark is sufficient then the watermark is detected in the input image. The distortion may be a spatially-variant distortion such as stretching, shrinking, shearing or rotation or the distortion may be a non-linear transforming or filtering such as median, local minimum or local maximum filtering.

Watermark detection

A method and arrangement for detecting a watermark in an information signal. The method may include the steps of computing the correlation (d ) of the watermark (W ) and the information signal (e.g. an image Q) for a plurality of positions (k) of the watermark with respect to the information signal, and detecting whether at least one of the respective correlation values exceeds a given threshold. The step of detecting may include determining the standard deviation (&sgr; ) of the respective correlation values (d ), and setting the threshold to a given multiple (T) of the standard deviation. The multiple (T) is derived form a desired false alarm rate (watermark detected when there is none, or no watermark detected when there is one).

A watermark detector is disclosed to judge whether multimedia content can be copied or not. The watermark detector examines the multimedia content and outputs a signal indicating whether a watermark is present or not. A decision variable indicating to which extent the watermark is present is determined, for example, the amount of correlation between the input signal and a reference copy of the watermark to be detected. The watermark is detected if the decision variable exceeds a predetermined threshold (y ). The detector also generates a random output signal for a predetermined range of decision values between the threshold (y ) and a further threshold (y ).

Device for optically scanning a record carrier

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Eindhoven, Netherlands

Geert F G Depovere