Computing Distortion of Media Signals Using Embedded Data with Repetitive Structure and Log-Polar Mapping

• US 20070092108A1
• Filed: 12/19/2006
• Published: 04/26/2007
• Est. Priority Date: 08/15/2002
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Meyer, Joel, Alattar, Adnan
• Granted Patent: US 7,529,647 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• 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

Abstract

A digital watermark detection method uses a matched filtering technique on a log polar re-mapping of a watermarked signal to detect peaks associated with a repetitive structure of a watermark.

Claims

1. A computing apparatus to determine distortion of a signal with embedded data, said apparatus comprising:

electronic processing circuitry; and

memory, said memory comprising instructions for processing by said electronic processing circuitry, the instructions comprising instructions to;

transform the signal into a transform domain to produce peaks due to a repetitive structure of the embedded data in the signal;

perform a mapping of the transformed signal to convert distortion of the embedded data into a shift; and

perform a correlation of the mapped signal with a signal representing an expected pattern of peaks associated with the repetitive structure of the embedded data signal, wherein the correlation detects the shift, and the shift provides a measure of the distortion of the signal.

2. The apparatus of claim 1 wherein the instruction to transform comprises an autocorrelation of the signal.

3. The apparatus of claim 1 wherein the mapping includes a log-polar mapping to convert scaling and rotation into spatial shifts.

4. The apparatus of claim 1 wherein the correlation is computed using a matched filter.

5. The apparatus of claim 1 wherein the embedded signal is repeated in rectangular blocks.

6. The apparatus of claim 1 wherein the electronic processing circuitry and the memory are components of a special purpose digital circuit.

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

transforming the signal into a transform domain to emphasize a repetitive structure of the digital watermark in the signal;

performing a mapping of the transformed signal to convert geometric distortion of the digital watermark into a shift; and

performing a detection of the digital watermark in the mapped signal using an expected pattern corresponding to data embedded in the digital watermark.

8. The method of claim 7 wherein transforming comprises an autocorrelation of the signal to produce peaks associated with the repetitive structure.

9. The method of claim 7 wherein the mapping includes a log-polar mapping to convert scaling and rotation into spatial shifts.

10. The method of claim 7 wherein the detection is computed using a matched filter.

11. The method of claim 7 wherein the digital watermark is repeated in rectangular blocks in the signal.

12. The method of claim 7 wherein the mapping comprises a log mapping and the geometric distortion is time or spatial scaling.

13. The method of claim 7 wherein transforming comprises a frequency domain transform.

14. The method of claim 13 wherein the frequency domain transform includes a Fourier transform.

15. A tangible medium on which is stored instructions for performing the method of claim 7.

16. A method of detecting a digital watermark in an image signal comprising:

computing the autocorrelation of the image signal to emphasize a repetitive structure of the digital watermark in the signal;

performing a log polar mapping of the transformed signal to convert rotation and spatial scaling of the digital watermark into shifts; and

performing a detection of the digital watermark in the log polar mapped signal using a pattern corresponding to data embedded in the digital watermark.

17. The method of claim 16 wherein the image signal comprises a video signal.

18. The method of claim 16 wherein the digital watermark is embedded in the frequency domain of the image signal.

19. The method of claim 16 wherein the detection comprises a correlation operation.

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