Curve fitting for synchronizing readers of hidden auxiliary data

• US 7,391,881 B2
• Filed: 07/11/2006
• Issued: 06/24/2008
• Est. Priority Date: 12/18/2000
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Sharma, Ravi K.
• Primary Examiner(s): Johns; Andrew W.
• Application Number:
  US11/456,813
• Publication Number:
  US 20070154061A1
• Time in Patent Office: 714 Days
• Field of Search: 382/100, 382/232, 382/286, 382/287, 713/176, 348/461, 348/467
• 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: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: G10L 21/00 Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility G10L19/00 takes precedence
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32154 Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32352 Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence

Abstract

A curve fitting method is used to synchronize a reader of embedded data in a media signal. A circular reference signal is embedded in the media signal. After geometric distortion of the media signal, the reference signal is distorted, yet still detectable. The amount of distortion is derived by detecting the reference signal, and applying a curve fitting method from which the distortion is calculated.

Claims

1. A method of encoding a reference signal into an image comprising:

defining a reference signal comprising signal elements in a circular reference pattern; and

steganographically embedding the reference signal in perceptible content of the image such that geometric distortion of the image is derived by detecting the signal elements, fitting the detected elements to an ellipse and deriving affine parameters of the geometric distortion from the ellipse.

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

3. A method of encoding a reference signal into an image comprising:

defining a reference signal comprising signal elements in a circular reference pattern; and

embedding the reference signal in the image such that geometric distortion of the image is derived by detecting the signal elements, fitting the detected elements to an ellipse and deriving affine parameters of the geometric distortion from the ellipse;

wherein the reference signal carries auxiliary hidden information.

4. The method of claim 3 wherein the reference signal carries the auxiliary hidden information by varying location of reference points in the reference signal.

5. The method of claim 3 wherein the reference signal carries the auxiliary information by varying an arrangement of reference patterns.

6. A method of encoding a reference signal into an image comprising:

defining a reference signal comprising signal elements in a circular reference pattern; and

embedding the reference signal in the image such that geometric distortion of the image is derived by detecting the signal elements, fitting the detected elements to an ellipse and deriving affine parameters of the geometric distortion from the ellipse;

wherein the image is part of a video signal.

7. A method of synchronizing a reader of data embedded in an image comprising:

extracting a reference signal from the image comprising signal elements in a reference pattern;

the reference signal being steganographically embedded within perceptible content of the image;

fitting the detected elements to an ellipse; and

deriving affine parameters of the geometric distortion from the ellipse.

8. A computer readable medium on which is stored instructions for performing the method of claim 7.

9. The method of claim 7 wherein the image is part of a video signal.

10. The method of claim 7 wherein the reference signal is extracted by quantizing the image to map samples of the image into quantization bins and identifying elements of the reference signal in the quantized image.

11. A method of synchronizing a reader of data embedded in an image comprising:

extracting a reference signal from the image comprising signal elements in a reference pattern;

fitting the detected elements to an ellipse; and

deriving affine parameters of the geometric distortion from the ellipse;

wherein the reference signal carries auxiliary hidden information.

12. The method of claim 11 wherein the reference signal carries the auxiliary hidden information by varying location of reference points in the reference signal.

13. The method of claim 11 wherein the reference signal carries the auxiliary information by varying an anangement of reference patterns.

14. A method of synchronizing a reader of data embedded in an image comprising:

extracting a reference signal from the image comprising signal elements in a reference pattern;

fitting the detected elements to an ellipse; and

deriving affine parameters of the geometric distortion from the ellipse;

the method including;

filtering the image by applying a filter to an array of samples of the image, wherein the filter compares a center sample with each of a plurality of neighboring samples, for each comparison generates a result based on the comparison, sums the result, and replaces the center sample with the sum.

15. The method of claim 14 wherein the filter is implemented with a look up table that maps the comparison operation to the result.

16. The method of claim 14 wherein the reference signal is defined in a frequency domain and the samples comprise frequency domain samples of the image.

17. A method of synchronizing a reader of data embedded in an image comprising:

extracting a reference signal from the image comprising signal elements in a reference pattern;

fitting the detected elements to an ellipse; and

deriving affine parameters of the geometric distortion from the ellipse;

wherein the reference signal is defined in a transform domain of the image.

18. The method of claim 17 wherein the transform domain comprises a spatial frequency domain of the image.