Embedding data in material
First Claim
1. A method of embedding data in an information signal representing material, the method comprising:
- combining the information signal with a function of the data and a scaling factor, the data being recoverable from the combination by a decoding process;
wherein the information signal, prior to forming the combination, is subject to the decoding process as trial; and
the scaling factor is generated as a function of the trial decoding process.
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Abstract
A spatial domain image I produced by a source 1 is combined with watermark data Ri to produce a spatial domain watermarked image I′. The watermarked image is produced by an embedder 3 according to the equation
Ci′=Ci+α.Ri
where Ci and Ci′ are wavelet transform coefficients of the image, and a 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 it is too small the mark may not survive processing of the image.
α is determined from a trial decoding of the image I in a decoder 4. The decoding is that which would be used to decode the watermarked image I′. A value α′ is produced by a calculator S3-S8, to which an offset value is added by an adder S9 to produce α. This produces values of a over the image, which are used to scale the data Ri so as to conceal the data. An image is one example of material to which the invention is applicable.
The step of producing modified coefficient values Ci may not use coefficients of magnitude greater than a threshold T and does not use corresponding information symbols Ri. Alternatively, a threshold Tclip may be set. The scaling factor α is calculated using clipped coefficient values and coefficients Ci of magnitude less than Tclip.
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Citations
66 Claims
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1. A method of embedding data in an information signal representing material, the method comprising:
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combining the information signal with a function of the data and a scaling factor, the data being recoverable from the combination by a decoding process;
wherein the information signal, prior to forming the combination, is subject to the decoding process as trial; and
the scaling factor is generated as a function of the trial decoding process. - View Dependent Claims (2, 16)
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3. A method of embedding data in an information signal representing material comprising the steps of:
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combining, as a trial, a representation of the material with a function of the data and a trial scaling factor;
performing, as a trial, a predetermined process on the combined material and data;
Performing a trial decoding of the processed combined material and data; and
Adjusting the scaling factor as a function of the trial decoding of the processed combined material and data.
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4. A method of embedding data bits in material, the method comprising the steps of:
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producing transform coefficients Ci representing a transform of the material;
producing a pseudo random symbol stream having L symbols Pi of values +1 and −
1;
calculating a correlation S=Σ
Ci.Pi, for i=1 to i=L; and
calculating modified coefficient values Ci′
=Ci+α
*Pi, where α
is calculated dependent on S and the value of the data bit to be embedded in the coefficient. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18, 63)
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17. Apparatus for embedding data in an information signal representing material, the apparatus comprising:
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a combiner for producing a combination of the information signal with a function of the data and a scaling factor;
a decoder for decoding the information signal to recover the data therefrom; and
a generator for generating the scaling factor wherein the scaling factor is generated as a function of a trial decoding of the information signal prior to forming the combination.
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19. Apparatus for embedding data in an information signal representing material, comprising a combiner arranged to combine, as a trial, a representation of the material with a function of the data and a trial scaling factor:
and further comprising;
a processor for performing, a predetermined process on the combined information signal and data;
a decoder for recovering the data from the processed combined information signal and data and a generator for generating the scaling factor as a function of decoding of the processed combined information signal and data.
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20. Apparatus for embedding data in material, the apparatus comprising:
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a transformer for producing transform coefficients Ci representing a transform of the material;
a generator for producing a pseudo random symbol stream having L bits Pi;
an input for receiving symbol representing the data to be concealed; and
a data embedder arranged to calculate a correlation S=Y Ci*Pi, for i=1 to i=L and calculate modified coefficient values Ci′
=Ci+α
*Pi, where α
is calculated dependent on S and the value of the data bit to be embedded in the coefficient. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A method of embedding data in material, 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. - View Dependent Claims (33, 34, 35, 36, 37, 38, 40, 43, 60, 61, 62, 64)
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39. A method for detecting data embedded in material, the detecting method comprising
receiving transform coefficients of the material; -
comparing the magnitudes of the received coefficients with a threshold value T; and
correlating, the said coefficients with a respective symbols of a pseudo random symbol sequence to detect the said data, wherein the correlating step does not use coefficients of magnitude greater than the said threshold T and corresponding symbols of the pseudo random symbol sequence.
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41. A method of detecting data embedded in material, the method comprising;
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receiving 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. - View Dependent Claims (42, 65)
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44. A method of embedding data in material, the method comprising
receiving transform coefficients Ci representing the material; -
comparing the magnitudes of the said transform coefficients Ci with a threshold Tclip;
clipping, to the magnitude Tclip, the magnitudes of those of the coefficients having a magnitude exceeding Tclip to produce clipped coefficients, and producing modified coefficients Ci′
values dependent on a scaling factor and the data to be embedded, and the scaling factor is calculated using the said clipped coefficients and the coefficients Ci of magnitude less than Tclip. - View Dependent Claims (47, 48, 49, 50, 51, 52, 53, 59, 66)
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45. A computer program product arranged to carry out the method of 32, when run on a computer.
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46. Apparatus for embedding data in material, comprising:
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a transformer for producing transform coefficients Ci of the 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.
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54. Apparatus for detecting data embedded in material, the 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. - View Dependent Claims (55, 57)
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56. Apparatus for detecting data embedded in material, comprising:
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an input for receiving transform coefficients Ci′
of the material;
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 the 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 material.
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58. Apparatus for embedding data in material, the apparatus comprising:
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an input for receiving transform coefficients Ci representing the material;
a comparator for comparing the magnitudes of the said transform coefficients with a threshold Tclip;
a clipper for clipping, to the magnitude Tclip, the magnitudes of those of the coefficients having a magnitude exceeding Tclip; and
a processor for producing modified coefficients Ci′
values dependent on a scaling factor and the data to be embedded, and the scaling factor is calculated using the said clipped coefficients and the coefficients Ci of magnitude less than Tclip.
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Specification