Decoding watermark information items of a watermarked audio or video signal using correlation

US8041073B2 · kind B2 · utility

Assignee

• Thomson Licensing · FR

Inventors

• Peter Georg Baum · Hannover, DE
• Walter Voessing · Hannover, DE

Key dates

• Filing date: Dec 1, 2006
• Grant date: Oct 18, 2011
• Expiry date: Feb 1, 2029

Classification

• Technology area (CPC G): Physics
• CPC primary: G06T2201/0065
• WIPO field: Computer technology
• WIPO sector: Electrical engineering

Abstract

Watermark information consists of several data symbols which are embedded continuously in an audio or a video signal using modulation with a pseudo-random sequence if spread spectrum technology is used. At decoder site the watermark information is regained using correlation of the received signal with a candidate pseudo-random sequence. Such correlation can be performed by one-dimensional real-symmetric fast Fourier transform of the two input signal vectors, which each consist of a section of N values of the input signal, to which section N−1 zeroes are attached, by multiplying one of the transformed vectors by the conjugated version of the other transformed vector, followed by inverse RFFT transform of that frequency domain product vector. However, if the level of a spread-spectrum watermark is too low or if too much noise had been added during the transmission of the audio or video signals, the correlation does not show a clear peak, which means that the watermark information bits cannot be recovered. According to the invention, the correlation result is improved by setting to zero in the frequency domain frequency bins of the vector which do not have a positive impact on the cor…