Digital watermark detecting with weighting functions

• US 20030095685A1
• Filed: 08/26/2002
• Published: 05/22/2003
• Est. Priority Date: 01/11/1999
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Cognicity, Inc.
• Inventors: Zhu, Bin, Tewfik, Ahmed, Swanson, Mitchell D.
• Granted Patent: US 6,751,337 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 1/005 Robust watermarking, e.g. average attack or collusion attack resistant
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection
• CPC Class Codes: G06T 2201/0202 whereby the quality of watermarked images is measured; Measuring quality or performance of watermarking methods; Balancing between quality and robustness
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal

Abstract

A digital watermark detector uses weighting functions to enhance watermark detection. The weighting function applies more weight to parts of a digitally watermarked signal that are more robust to distortion. As such, the method provides for more reliable watermark detection, especially in applications where distortions, such as lossy compression or analog conversion, more accurate detection more difficult. In one version of the method, the detector projects the watermarked signal into a pseudorandom direction specified by a key, applies the weighting function, and extracts auxiliary data symbols from the projected signal by quantizing the projected signal and deriving the symbol values based on the quantization.

Claims

1. A method of detecting a digital watermark in a media signal comprising:

computing a weighting function of a digitally watermarked signal;

applying the weighting function to the digitally watermarked signal to compute a weight-adjusted signal in which parts of the digitally watermarked signal that are more robust to distortion are weighted more than parts that are less robust to the distortion; and

recovering embedded auxiliary data symbols from the weight-adjusted signal.

2. The method of claim 1 including projecting the digitally watermarked signal according to a key.

3. The method of claim 2 wherein the key is pseudorandom.

4. The method of claim 1 wherein the weighting function is computed as a function of transform coefficients of the digitally watermarked signal.

5. The method of claim 1 wherein the digitally watermarked signal comprises an audio signal, and the weighting function is computed as a function of subband coefficients in critical bands of the audio signal.

6. The method of claim 5 wherein the weighting function is computed independently for the critical bands.

7. The method of claim 1 wherein the weighting function is robust to distortion of the digitally watermarked signal in terms of relative error before and after the distortion.

8. The method of claim 7 wherein the distortion comprises lossy data coding of the digitally watermarked signal.

9. The method of claim 1 wherein the weighting function estimates tolerable error level of one or more data samples in the media signal such that human perceptible error introduced by the digital watermark is minimized.

10. The method of claim 9 wherein the weighting function emulates a perceptual model applied for lossy compression of the media signal.

11. The method of claim 1 wherein applying the weighting function comprises dividing a projection of the digitally watermarked signal by the weighting function.

12. The method of claim 11 wherein the projection is computed by projecting the digitally watermarked signal according to a key.

13. The method of claim 12 wherein the projection comprises a projection onto a pseudorandom vector.

14. A computer readable medium on which is stored instructions for performing the method of claim 1.

15. A method of detecting a digital watermark in a media signal comprising:

computing a weighting function of a digitally watermarked signal;

projecting the digitally watermarked signal into a direction according to a key;

applying the weighting function to the projected signal to compute a projected signal in which parts of the digitally watermarked signal that are more robust to distortion are weighted more than parts that are less robust to the distortion; and

recovering embedded auxiliary data symbols from the projected signal.

16. The method of claim 15 wherein the direction comprises a pseudorandom direction.

17. The method of claim 15 wherein the weighting function is robust to distortion of the digitally watermarked signal in terms of relative error before and after the distortion.

18. A computer readable medium on which is stored instructions for performing the method of claim 15.

19. A method of detecting a digital watermark in a media signal comprising:

computing a weighting function of a digitally watermarked signal;

projecting the digitally watermarked signal into a direction according to a key;

applying the weighting function to the projected signal to compute a projected signal in which parts of the digitally watermarked signal that are more robust to distortion are weighted more than parts that are less robust to the distortion; and

recovering embedded auxiliary data symbols from the projected signal by quantizing the projected signal to determine a binary symbol associated with a quantization of the projected signal.

20. A computer readable medium on which is stored instructions for performing the method of claim 19.