On Thursdays the USPTO publishes pending patent applications. Both of today's Spotlight Applications address aspects of digital watermarking. Assigned to AT&T, the first application discloses techniques for retrieving a watermark within a signal. Assigned to Thomson, the second application discloses techniques for determining whether or not a reference pattern is present in a received and possibly watermarked signal.
20090185692, "System and Method of Retrieving a Watermark Within a Signal," assigned to AT&T.
Abstract
A system and method of retrieving a watermark in a watermarked signal are disclosed. The watermarked signal comprises odd and even overlapped blocks where the watermark is contained in the even blocks. The method comprises, for each k-th even block, subtracting the two adjacent odd numbered blocks from the k-th even block of the watermarked signal to retrieve s*.sub.k(n), transforming s*.sub.k(n) into the frequency domain to generate S.sub.k(f), calculating a phase of S.sub.k(f) as .phi.(f) and a phase of S.sub.k(f) as .phi.(f), calculating the difference .PSI.(f) between .phi.(f) and .phi.(f), unwrapping .PSI.(f) to obtain the phase modulation {tilde over (.PHI.)}.sub.k(f), and using a Viterbi search to retrieve the watermark embedded in {tilde over (.PHI.)}.sub.k(f).
20090187765, "Method and apparatus for determining whether or not a reference pattern is present in a received and possibly watermarked signal," assigned to Thomson Licensing.
Abstract
Many watermarking systems make use of correlation for calculating a detection metric, which means that several reference patterns are generated at encoder side and one or more of them are embedded inside the content signal, dependent on the message to be embedded. To decode the embedded message, it is necessary to discover which reference pattern was embedded at encoder side. This is determined by correlating the known reference patterns with the content signal. A watermark detector decides, depending on the size of the correlation result values, whether or not a given pseudo-random sequence was embedded. However, this does not provide correct decisions if watermarked audio is emitted by a loudspeaker and then captured with a microphone. According to the invention, it is taken advantage of the received signal echoes instead of treating them as noise. The watermark detection result is improved by integrating the correlation values resulting from echoes into the main correlation peak, thereby using correlation result amplitude values located within a predetermined neighborhood of a correlation result peak amplitude value and exceeding a predetermined threshold.
