Patent ID: 8050446

Claim:
A method for applying a digital watermark to a signal, comprising the steps of: (a) dividing the signal into a plurality of fragments; (b) recursively performing an inverse difference pyramid decomposition with respect to said fragments, resulting in a plurality of pyramid levels each comprising a set of spectrum coefficients; (c) calculating an adaptive threshold for each of the plurality of pyramid levels, wherein the adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest spectrum coefficient and (ii) a predefined small positive value, and selecting a subset of spectrum coefficients from the set of spectrum coefficients based on the value of the adaptive threshold; (d) modifying the subset of spectrum coefficients with a watermark, resulting in a set of watermarked spectrum coefficients; and (e) constructing from said set of watermarked spectrum coefficients and those of the spectrum coefficients that are not modified a watermarked signal.