Embedding data in material
First Claim
1. A method of embedding data in an information signal representing material, said method comprising the steps of:
- producing transform coefficients Ci of the material;
comparing the magnitudes of the coefficients with a threshold value T; and
producing modified coefficient value Ci′
by adding an additive offset to the coefficient Ci, wherein said offset is an information symbol of a pseudo random symbol sequence modulated by said data to be embedded;
wherein said step of producing modified coefficient values does not use coefficients of magnitude greater than the said threshold T and does not use the corresponding information symbols of the pseudo random symbol sequence, the value of said threshold T being set to reduce a likelihood of any coefficient having a dominant effect on a correlation of the pseudo random symbol sequence and the information signal in which the data has been embedded.
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Accused Products
Abstract
A spatial domain using image produced by a source is combined with watermark data Ri to produce a spatial domain watermarked image. The watermarked image is produced by an embedder according to equation: Ci′=Ci+α. Ri, where Ci and Ci′ are wavelet transform coefficients of the image, and α is a scaling factor. α is chosen so that the watermark is imperceptible in the image and to resist removal of the watermark by unauthorized processing. It is desirable that a has the smallest value which achieves that. If α is too big the watermark is perceptible in the image. If α is too small the mark may not survive processing of the image.
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Citations
57 Claims
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1. A method of embedding data in an information signal representing material, said method comprising the steps of:
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producing transform coefficients Ci of the material; comparing the magnitudes of the coefficients with a threshold value T; and producing modified coefficient value Ci′
by adding an additive offset to the coefficient Ci, wherein said offset is an information symbol of a pseudo random symbol sequence modulated by said data to be embedded;wherein said step of producing modified coefficient values does not use coefficients of magnitude greater than the said threshold T and does not use the corresponding information symbols of the pseudo random symbol sequence, the value of said threshold T being set to reduce a likelihood of any coefficient having a dominant effect on a correlation of the pseudo random symbol sequence and the information signal in which the data has been embedded. - View Dependent Claims (2, 3, 4, 5, 6, 7, 9, 10, 11)
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8. A computer program product embodied in a computer readable medium arranged to carry out the method of 1, when run on a computer.
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12. Apparatus for embedding data in an information signal representing material, said apparatus comprising:
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a transformer for producing transform coefficients Ci of the information signal; a comparator for comparing the magnitudes of the coefficients with a threshold value T; and a combiner for producing modified coefficient value Ci′
by adding an additive offset to the coefficient Ci, wherein said offset is an information symbol of a pseudo random symbol sequence modulated by said data to be embedded;wherein the combiner does not use coefficients of magnitude greater than said threshold T and does not use the corresponding information symbols of the pseudo random symbol sequence, the value of said threshold T being set to reduce a likelihood of any coefficient having a dominant effect on the correlation of the pseudo random symbol sequence and the information signal in which the data has been embedded. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A method for detecting data embedded in an information signal representing material, the detecting method comprising:
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receiving transform coefficients of the information signal; comparing the magnitudes of the received coefficients with a threshold value T; and correlating, said coefficients with respective symbols of a pseudo random symbol sequence to detect said data, wherein the correlating step does not use coefficients of magnitude greater than said threshold T and corresponding symbols of the pseudo random symbol sequence. - View Dependent Claims (21, 22)
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23. A method of detecting data embedded in an information signal representing material, the method comprising the steps of:
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receiving transform coefficients of the information signal; comparing the magnitudes of the received coefficients with a threshold Tclip; clipping, to a magnitude Tclip, the magnitude of coefficients of magnitude greater than said threshold Tclip; and correlating the clipped and unclipped coefficients with a pseudo random symbol sequence to detect data embedded in the information signal. - View Dependent Claims (24, 25)
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26. A method of embedding data in an information signal representing material, said method comprising the steps of:
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producing transform coefficients Ci of the material; comparing the magnitudes of the coefficients with a threshold value T; and producing, from the coefficients Ci and the said data, modified coefficient values Ci′
which are modified by respective information symbols of a pseudo random symbol sequence modulated by the said data to be embedded;wherein the said step of producing modified coefficient values does not use coefficients of magnitude greater than the said threshold T and does not use the corresponding information symbols; and
detecting the data byreceiving transform coefficients of the material; comparing the magnitudes of the received coefficients with a threshold Tclip; clipping, to a magnitude Tclip, the magnitude of coefficients of magnitude greater than the said threshold Tclip; and correlating the clipped and unclipped coefficients with a pseudo random symbol sequence to detect data embedded in the material.
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27. Apparatus for detecting data embedded in an information signal representing material, the detecting apparatus comprising:
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an input for receiving transform coefficients of an information signal; a comparator for comparing the magnitudes of the received coefficients with a threshold T; and a correlator for correlating said coefficients with respective symbols of a pseudo random symbol sequence to detect said data, wherein the correlation does not use coefficients of magnitude greater than the said threshold T and the corresponding symbols of the pseudo random symbol sequence. - View Dependent Claims (28)
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29. Apparatus for detecting data embedded in an information signal representing material, said apparatus comprising:
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an input for receiving transform coefficients Ci′
of the information signal;a comparator for comparing the magnitudes of the received coefficients with a threshold Tclip; a clipper for clipping, to a magnitude Tclip, the magnitude of coefficients of magnitude greater than said threshold T; and a correlator for correlating the clipped and unclipped coefficients with a pseudo random symbol sequence to detect data embedded in the information signal. - View Dependent Claims (30)
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31. A system including an embedding apparatus, said system comprising:
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a transformer for producing transform coefficients Ci of an information signal representing material, a comparator for comparing the magnitudes of the coefficients with a threshold value T, and a combiner for producing, from the coefficients Ci and the said data, modified coefficient values Ci′
which are modified by respective information symbols of a pseudo random symbol sequence modulated by the said data to be embedded, wherein the combiner does not use coefficients of magnitude greater than the said threshold T and does not use the corresponding information symbols; and
detecting apparatus comprising;an input for receiving transform coefficients of the material; a comparator for comparing the magnitudes of the received coefficients with a threshold T; and a correlator for correlating the said coefficients with respective symbols of a pseudo random symbol sequence to detect the said data, wherein the correlation does not use coefficients of magnitude greater than the said threshold T and the corresponding symbols of the pseudo random symbol sequence.
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32. A method of embedding data in an information signal representing material, the method comprising the steps of:
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producing transform coefficients Ci representing a transform of the information signal; producing a pseudo random symbol stream having L symbols Pi, the pseudo random symbol stream comprising symbol values of +1 or −
1;calculating a correlation value S=Σ
Ci*Pi for i=1 to L; andcalculating modified coefficient values Ci′
=Ci+α
*Pi, where α
is calculated dependent on the value of S being positive or negative to identify a corresponding binary value of the data symbol being embedded. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45)
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46. An apparatus for embedding data in an information signal representing material, the apparatus comprising:
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a transformer for producing transform coefficients Ci representing a transform of the information signal; a generator for producing a pseudo random symbol stream having L symbols Pi, the pseudo random symbol stream comprising symbol values of +1 or −
1;an input for receiving symbols of the data to be embedded; and a data embedder arranged to calculate a correlation value S=Σ
Ci*Pi for i=1 to L; andto calculate modified coefficient values Ci′
=Ci+α
*Pi, where α
is calculated dependent on the value of S being positive or negative to identify a corresponding binary value of the data symbol being embedded. - View Dependent Claims (47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57)
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Specification