Method and apparatus for quantisation index modulation for watermarking an input signal

Patent metadata

Field	Value
Publication number	US-10019997-B2
Application number	US-201214131027-A
Country	US
Kind code	B2
Filing date	Jun 25, 2012
Priority date	Jul 8, 2011
Publication date	Jul 10, 2018
Grant date	Jul 10, 2018

Abstract

With quantization index modulation QIM it is possible to achieve a very high data rate, and the capacity of the watermark transmission is mostly independent of the characteristics of the original audio signal, but the audio quality suffers from degradation with each watermark embedding-and-removal step. In order to avoid degradation of the audio quality, the inventive audio signal watermarking uses specific quantizer curves in time domain and in particular in frequency domain for embedding the watermark message into the audio signal, whereby the processing is almost perfectly reversible. Furthermore, it has embedded a power constraint in order to guarantee that the modifications of the audio signal due to the watermark embedding are inaudible.

First claim

The invention claimed is:

1. An apparatus for quantisation index modulation for watermarking an input signal x, wherein different quantiser curves Q m are used for quantising said input signal x and a current characteristic of said quantiser curves is controlled by a current content of a watermark message m to be embedded into said input signal x so as to form a watermarked output signal y from which said input signal x and said watermark message m can be recovered, said apparatus comprising:
at least one input adapted to receive said input signal x and the watermark signal m,
at least one processor adapted to quantise, using said quantiser curves Q m , said input signal x, a current quantiser curve Q m being selected for quantizing a current content of said input signal x so that the current characteristic of said current quantiser curve Q m corresponds to the current content of said watermark signal m, and an input value of said input signal x being transformed to an output value of said output signal y according to said selected current quantiser curve Q m , wherein the difference between input value and output value at any position is not greater than T, and said quantising curves Q m are reversible in that for any output value of the output signal y there is a unique input value of the input signal x,

said at least one processor being further configured to define the y shift towards y=0 of outer sections of said quantiser curves Q m by a value ±T, which is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal, and to establish the different quantiser curves Q m according to the current value of m by different shifts of the complete quantiser curve in x direction,
at least one output adapted to output the watermarked output signal y obtained from quantizing said input signal x with said quantiser curves Q m , wherein said input signal x is an audio signal or a video signal, wherein the output signal y is configured to avoid degradation upon playback.

2. The apparatus according to claim 1 , wherein said quantising is carried out according to y=Q m (x)+max(x−T,min(x+T,α(x−Q m (x)))), wherein α is a predetermined steepness of the medium section of said quantiser curves Q m , ±T is a value defining the y shift towards y=0 of the other sections of said quantiser curves Q m and is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal.

3. The apparatus according to claim 1 , wherein said quantising is carried out in frequency domain.

4. The apparatus according to claim 3 , in which said at least one processor is further configured for time-to-frequency transform and frame pair combining, wherein of every successive frame pair one frame is treated as representing a real part of one current frame and the other frame is treated as representing an imaginary part of that current frame, and for frequency-to-time transform, so as to form said watermarked output signal y.

5. The apparatus according to claim 4 , wherein said time-to-frequency transform is an MDCT and said frequency-to-time transform is an IMDCT.

6. The apparatus according to claim 4 , wherein said quantizing is applied to phases of individual coefficients of a complex spectrum given by said real part and said imaginary part corresponding to said every successive frame pair.

7. An apparatus for regaining an original input signal x which has been processed by quantizing, by an embedder and using different quantiser curves Q m , the input signal x, a current characteristic of said quantiser curve being controlled by a current content of a watermark message m embedded in said input signal x so as to form a watermarked output signal y from which said input signal x and said watermark message m can be recovered, a current quantiser curve Q m being selected for quantizing a current content of said input signal x so that the current characteristic of said current quantiser curve Q m corresponds to the current content of said watermark signal m, and an input value of said input signal x being transformed to an output value of said output signal y according to said selected current quantiser curve Q m , wherein in said quantising the difference between input value and output value at any position is not greater than T, and that said quantising curves Q m are reversible in that for any output value of the output signal y there is a unique input value of the input signal x, defining, by a psycho-acoustic masking level calculator, the y shift towards y=0 of outer sections of said quantiser curves Q m by a value ±T, which is determined by the current psycho-acoustic masking level of said input signal x, and y is the watermarked output signal, and establishing the different quantiser curves Q m according to the current value of m by different shifts of the complete quantiser curve in x direction, said apparatus comprising:
at least one input adapted to receive the output signal y,
at least one processor configured for re-quantising the received watermarked signal using said quantiser curves Q m in a corresponding manner, wherein different candidate quantiser curves Q m are checked by applying different shifts of the complete quantiser curve in x direction, and wherein said re-quantisation is carried out with a bit depth that is greater than the bit depth that was applied originally;
said at least one processor being further configured to select that candidate quantiser curve Q m which matches best in the frequency domain, and based on the current Q m so determined, to remove the corresponding current watermark signal m from signal y so as to provide said regained signal x,
at least one output adapted to output said regained signal x and said corresponding current watermark signal m, wherein said input signal x is an audio signal or a video signal, wherein the output signal y is configured to avoid degradation upon playback.

8. A method for quantisation index modulation for watermarking an input signal x, comprising:
receiving said input signal x and a watermark signal m at least one input, quantising, by at least one processor and using different quantiser curves Q m , said input signal x, a current characteristic of said quantiser curves being controlled by a current content of the watermark message m to be embedded into said input signal x so as to form a watermarked output signal y from which said input signal x and said watermark message m can be recovered, a current quantiser curve Q m being selected for quantizing a current content of said input signal x so that the current characteristic of said current quantiser curve Q m corresponds to the current content of said watermark signal m, and an input value of said input signal x being transformed to an output value of said output signal y according to said selected current quantiser curve Q m , wherein in said quantising the difference between input value and output value at any position is not greater than T, and that said quantising curves Q m are reversible in that for any output value of the watermarked output signal y there is a unique input value of the input signal x,
defining, by said at least one processor, the y shift towards y=0 of outer sections of said quantiser curves Q m by a value ±T, which is determined by the current psycho-acoustic masking level of said input signal x,
establishing by said at least one processor the different quantiser curves Q m according to the current value of m by different shifts of the complete quantiser curve in x direction,
outputting the watermarked output signal y obtained from quantizing said input signal x with said quantiser curves Q m at at least one output, wherein sa

Assignees

• Jax Peter
• Thomson Licensing

Inventors

• Jax Peter

Classifications

• G10L19/008

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title

• G10L19/035

  Scalar quantisation · CPC title

• G10L21/038

  using band spreading techniques · CPC title

• G10L19/24

  Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding · CPC title

• G10L19/018 Primary

  Audio watermarking, i.e. embedding inaudible data in the audio signal · CPC title