Method and system for digital watermarking of multimedia signals

A method of watermarking a signal, comprising the steps of:

• (a) dividing the signal into fragments;
• (b) performing a truncated complex orthogonal transform with respect to each fragment, resulting in an approximation of the signal comprising a set of zero-level spectrum coefficients;
• (c) calculating a zero-level adaptive threshold, wherein the zero-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest zero-level spectrum coefficient and (ii) a predefined small positive value, and selecting a subset of the set of zero-level spectrum coefficients based on the value of the zero-level adaptive threshold, then applying a first set of watermark data to the subset of the set of zero-level spectrum coefficients;
• (d) calculating a difference between the signal and the approximation of the signal with respect to each fragment;
• (e) dividing the calculated difference into a plurality of sub-fragments;
• (f) performing a truncated complex orthogonal transform with respect to each sub-fragment, resulting in a set of first-level spectrum coefficients;
• (g) calculating a first-level adaptive threshold, wherein the first-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest first-level spectrum coefficient and (ii) the predefined small positive value, and selecting a subset of the set of first-level spectrum coefficients based on the value of the first-level adaptive threshold, then applying a second set of watermark data to the subset of the set of first-level spectrum coefficients;
• (h) performing a series of inverse complex orthogonal transforms with respect to said fragments and sub-fragments, and adding to the result of such transforms a part of the signal which remained unchanged, resulting in a watermarked signal.

A method for extracting a digital watermark from a first signal utilizing a second signal, comprising the steps of:

• (a) dividing the first and second signals into a plurality of fragments;
• (b) recursively performing an inverse difference pyramid decomposition with respect to the fragments, resulting in a plurality of pyramid levels each comprising a set of spectrum coefficients with respect to each signal;
• (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) comparing the subset of the spectrum coefficients from the first signal with the subset of the spectrum coefficients from the second signal obtaining a comparison result;
• and
• (e) assembling a watermark from the first signal by means of inverse permutations with respect to the comparison result.

A method of extracting a watermark from a first signal utilizing a second signal not containing a watermark, comprising the steps of:

• (a) dividing the first signal and the second signal into fragments;
• (b) performing a truncated complex orthogonal transform with respect to each fragment, resulting in an approximation of the signals comprising a set of zero-level spectrum coefficients;
• (c) calculating a zero-level adaptive threshold, wherein the zero-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest zero-level spectrum coefficient and (ii) a predefined small positive value, and selecting a subset of the set of zero-level spectrum coefficients based on the value of the zero-level adaptive threshold, then comparing the subset of zero-level spectrum coefficients of the first signal to the subset of zero-level spectrum coefficients of the second signal to extract a zero-level difference of spectrum coefficients;
• (d) calculating a difference between each signal and an approximation of each signal with respect to each fragment;
• (e) dividing the calculated difference into a plurality of sub-fragments;
• (f) performing a truncated complex orthogonal transform with respect to each sub-fragment of each signal, resulting in a set of first-level spectrum coefficients;
• (g) calculating a first-level adaptive threshold, wherein the first-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest first-level spectrum coefficient and (ii) the predefined small positive value, and selecting a subset of the set of first-level spectrum coefficients based on the value of the first-level adaptive threshold, then comparing the subset of first-level spectrum coefficients of the first signal to the subset of first-level spectrum coefficients of the second signal to extract a first-level difference of spectrum coefficients;
• and
• (h) combining the zero-level difference of spectrum coefficients with the first-level difference of spectrum coefficients to result in a watermark.

A method for detecting a digital watermark in 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 the fragments of the signal, resulting in a plurality of pyramid levels comprising a set of spectrum coefficients with respect to the signal;
• (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 utilizing the adaptive threshold at each of the plurality of pyramid levels to select a subset of spectrum coefficients;
• (d) comparing the subset of the spectrum coefficients with the watermark to obtain a comparison result;
• and
• (e) comparing a detection threshold with the comparison result to determine if the watermark is found in the signal.

A method of detecting a watermark in a signal, comprising the steps of:

• (a) dividing the signal into fragments;
• (b) performing a truncated complex orthogonal transform with respect to each signal fragment, resulting in an approximation of the signal comprising a set of zero-level spectrum coefficients;
• (c) calculating a zero-level adaptive threshold, wherein the zero-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest zero-level spectrum coefficient and (ii) a predefined small positive value, utilizing the zero-level adaptive threshold to produce a subset of zero-level spectrum coefficients, and comparing the subset of zero-level spectrum coefficients of the signal to a corresponding watermark element to generate a zero-level watermark result;
• (d) calculating a difference between each signal and the approximation of each signal with respect to each fragment;
• (e) dividing the calculated difference into a plurality of sub-fragments;
• (f) performing a truncated complex orthogonal transform with respect to each sub-fragment of the signal, resulting in a set of first-level spectrum coefficients;
• (g) calculating a first-level adaptive threshold, wherein the first-level adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest first-level spectrum coefficient and (ii) the predefined small positive value, utilizing the first-level adaptive threshold to produce a subset of first-level spectrum coefficients, and comparing the subset of first-level spectrum coefficients of the signal to a corresponding watermark element to generate a first-level watermark result;
• and
• (h) comparing a detection threshold with a construction based on the zero-level watermark result and first-level watermark result to determine if the watermark is found in the signal.

An apparatus for applying a watermark to a signal, comprising:

• (a) a transform module comprising a plurality of discrete electronic components operable to receive a segment of the signal and recursively derive a set of spectrum coefficients;
• (b) a permutation module operable to receive the watermark and a key and return an encoded watermark;
• (c) an adaptive threshold module operable to calculate an adaptive threshold 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;
• (d) a comparator and summator module collectively operable to select a subset of spectrum coefficients from the set of spectrum coefficients based on the value of the adaptive threshold;
• (e) a watermarking module operable to receive the subset of the set of spectrum coefficients from said summator module and said encoded watermark from said permutation module and return a transformed watermarked signal comprising a set of modified spectrum coefficients;
• and
• (f) an inverse transform module operable to receive a transformed watermarked signal comprising a set of modified spectrum coefficients and those of the spectrum coefficients that are not modified and return a watermarked signal.

An apparatus for extracting a watermark from a first signal utilizing a second signal, comprising:

• (a) a first transform module comprising a plurality of discrete electronic components operable to receive the first signal and recursively derive a first set of spectrum coefficients;
• (b) a second transform module operable to receive the second signal, and to calculate and return a second set of spectrum coefficients;
• (c) an adaptive threshold module operable to produce a first adaptive threshold from which a first subset of spectrum coefficients based on the first set of spectrum coefficients is selected, wherein the first adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest spectrum coefficient from the first set of spectrum coefficients and (ii) a predefined small positive value, and to produce a second adaptive threshold from which a second subset of spectrum coefficients based on the second set of spectrum coefficients is selected wherein the second adaptive threshold is calculated as the greater of (i) a fraction of a module of a largest spectrum coefficient from the second set of spectrum coefficients and (ii) the predefined small positive value;
• (d) a comparator module operable to calculate a difference between the first subset of the first set of spectrum coefficients with the second subset of the second set of spectrum coefficients and return a transformed encoded watermark;
• and
• (e) an inverse transform module operable to receive a key and the transformed encoded watermark and return the watermark.

An apparatus for detecting a watermark in a signal, comprising:

• (a) a transform module comprising a plurality of discrete electronic components operable to receive a segment of the signal and recursively derive a set of spectrum coefficients;
• (b) a permutation module operable to receive the watermark and a key and return an encoded watermark;
• (c) an adaptive threshold module operable to calculate an adaptive threshold 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;
• (d) a comparator and summator module collectively operable to select a subset of spectrum coefficients from the set of spectrum coefficients based on the value of the adaptive threshold;
• (e) a correlation module operable to determine a watermark correlation factor between the subset of spectrum coefficients and the encoded watermark;
• and
• (f) a watermark comparator module operable to compare the watermark correlation factor to a watermark threshold, and return a watermark detection result.