Encoded reference signal for digital watermarks

• US 20030012401A1
• Filed: 04/24/2002
• Published: 01/16/2003
• Est. Priority Date: 04/25/2001
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Stach, John, Sharma, Ravi K.
• Granted Patent: US 7,046,819 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

Abstract

This disclosure describes a method for encoding a digital watermark into an image signal that is robust to geometric distortion. The digital watermark is adapted to the host image signal in which it is embedded so as to be imperceptible or substantially imperceptible in the watermarked image when displayed or printed. This digital watermark may be used to determine the geometric distortion applied to a watermarked image, may be used to carry auxiliary information, and may be used to detect and decode a digital watermark embedded in a geometrically distorted version of a watermarked image. Because of its robustness to geometric distortion, the digital watermark is useful for a number of applications for embedding auxiliary data in image signals, including still pictures and video, where the image signal is expected to survive geometric distortion.

This method may adapted to other types of media signals such as audio.

Claims

1. A method for imperceptibly embedding auxiliary data in a media signal comprising:

setting magnitudes of a reference signal in an encoded domain;

transforming the reference signal to a first domain;

in the first domain, setting phase of the reference signal;

transforming the magnitude and phase of the reference signal from the first domain to a perceptual domain of the media signal; and

combining the reference signal with the media signal, including perceptually adapting the reference signal to the media signal.

2. The method of claim 1 wherein the media signal is an image signal and the perceptual domain comprises a spatial domain of the image.

3. The method of claim 1 wherein the phase of the reference signal is pseudorandom.

4. The method of claim 3 wherein the pseudorandom phase is created by spread spectrum modulating an N bit message with a pseudorandom number sequence.

5. The method of claim 1 wherein selected coefficients of the reference signal are set to encode an N bit message.

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

7. A method for decoding a digital watermark signal imperceptibly embedded in a media signal comprising:

creating a reference signal in an encoded domain;

correlating the reference signal with the media signal to determine at least a first distortion parameter;

using the first distortion parameter to align the media signal;

correlating a phase specification of the reference signal with the aligned media signal to determine a second distortion parameter;

using the second distortion parameter to decode the digital watermark from the media signal.

8. The method of claim 7 wherein an N bit message is decoded from phase information of the media signal by correlating the phase information with pseudorandom carrier signal.

9. The method of claim 7 wherein an N bit message is decoded from magnitude information of the watermarked signal in the encoded domain.

10. The method of claim 9 including:

detecting peaks in the encoded domain of the watermarked signal;

interpreting the peaks at predetermined locations as symbol values;

spread spectrum demodulating the symbol values to compute an error correction encoded signal; and

error correction decoding the error correction encoded signal to compute the N bit message.

11. The method of claim 9 including:

detecting peaks in the encoded domain of the watermarked signal;

interpreting the peaks at predetermined locations as symbol values; and

error correction decoding the symbol values to compute the N bit message.

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