Watermarking in the time-frequency domain

• US 20040267533A1
• Filed: 01/05/2004
• Published: 12/30/2004
• Est. Priority Date: 09/14/2000
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: DMRC Corporation
• Inventors: Levy, Kenneth L., Hannigan, Brett T.
• Granted Patent: US 7,330,562 B2
• Time in Patent Office: Days
• US Class Current: 704/273
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 21/8358 involving watermark protecting executable software by watermarking G06F21/16; image watermarking in general G06T1/0021; watermarks inserted in still images for transmission purposes H04N1/32144; inserting watermarks during video coding H04N19/467

Abstract

Methods and systems for time-frequency domain watermarking of media signals, such as audio and video signals. An encoding method divides the media signal into segments, transforms each segment into a time-frequency representation, and computes a time-frequency domain watermark signal based on the time frequency representation. It then combines the time-frequency domain watermark signal with the media signal to produce a watermarked media signal. To embed a message using this method, one may use peak modulation, pseudorandom noise modulation, statistical feature modulation, etc. Watermarking in the time-frequency domain enables the encoder to perceptually model time and frequency attributes of the media signal simultaneously. A watermark decoder uses a calibration signal to detect the watermark signal in a potentially distorted version of the watermarked signal. The calibration signal may also be used to determine the watermark'"'"'s alignment and scaling. After compensating for the alignment and scaling, a watermark reader extracts an embedded message from a time frequency representation of the media signal.

Claims

1. A method of watermarking a media signal with a temporal component, the method comprising:

dividing the media signal into segments,

transforming each segment into a time-frequency spectrogram,

computing a time-frequency domain watermark signal based on the time frequency spectrogram,

combining the time-frequency domain watermark signal with the media signal to produce a watermarked media signal.

2. The method of claim 1 wherein the time frequency domain watermark signal is computed based on a perceptual analysis of the time-frequency spectrogram.

3. A computer readable medium having software for performing the method of claim 1.

4. A system for watermarking a media signal comprising:

means for dividing a media signal into segments;

means for transforming the segments into a time frequency representation;

means for computing a watermark from the time frequency representation of the media signal and an auxiliary message to be encoded in the watermark; and

means for combining the watermark with the media signal to create a watermarked signal.

5. The system of claim 4 wherein the media signal comprises an audio signal.

6. A method of decoding a watermark from a media signal comprising:

transforming the media signal to a time frequency representation;

computing elements of a message signal embedded into the media signal from the time frequency representation; and

decoding a message from the elements.

7. The method of claim 6 including:

spread spectrum demodulating the message from the message elements.

8. A computer readable medium having software for performing the method of claim 6.

9. A digital watermark decoder comprising:

a detector for determining whether a watermark is present in the media signal and determining an alignment and scale of the watermark; and

a reader for decoding an auxiliary message embedded in a time frequency representation of the media signal, the auxiliary message being embedded in a two dimensional pseudorandom array in a time frequency representation of the media signal.

10. A method of decoding a watermark from a media signal comprising:

transforming the media signal into the time-frequency domain and reading the watermark from the transformed media signal.

11. The method of claim 10 wherein transforming includes separating the signal into blocks.

12. The method of claim 10 wherein transforming includes using a Fourier transform on windowed segments within each block.

13. The method of claim 10 including:

using a synchronization signal to determine the correct scaling and alignment before converting to the time-frequency domain.

14. The method of claim 13 wherein the synchronization signal comprises a set of impulse functions in a Fourier domain.

15. A computer readable medium having software for performing the method of claim 10.