Wavelet based feature modulation watermarks and related applications

• US 6,714,683 B1
• Filed: 08/24/2000
• Issued: 03/30/2004
• Est. Priority Date: 08/24/2000
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Tian, Jun, Decker, Stephen K.
• Primary Examiner(s): Patel, Jayanti K.
• Assistant Examiner(s): Choobin, Barry
• Application Number:
  US09/645,779
• Time in Patent Office: 1,314 Days
• Field of Search: 382/100, 382/240, 375/130, 713/176, 380/210, 380/51, 702/191, 707/100
• US Class Current: 382/240
• 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 1/3216 using Fourier transforms
• CPC Class Codes: H04N 1/3217 using wavelet transforms
• CPC Class Codes: H04N 1/32187 with selective or adaptive application of the additional information, e.g. in selected frequency coefficients
• CPC Class Codes: H04N 1/32283 Hashing
• 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
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/3236 Details of authentication information generation
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

A watermark embedder decomposes a media signal from its perceptual domain to subbands and embeds a message signal in the edge information of neighboring coefficients of those subbands. A compatible watermark decoder decomposes the watermarked signal into subbands and demodulates the message signal from the edge information of neighboring coefficients. In addition to the message signal, the embedder may also encode an orientation signal to synchronize the decoder with the embedded signal in a distorted version of the watermarked signal. The watermark system may be used in a variety of applications, including robustly carrying metadata or links to metadata, and to detect alterations of the watermarked signal, such as alterations due to printing, scanning, compression, etc.

Claims

1. A method for embedding auxiliary information in a media signal such that the auxiliary information is substantially imperceptible, the method comprising:

decomposing the media signal from a perceptual domain to subbands, each subband including a set of coefficients within a frequency range;

embedding a message signal having two or more elements into at least one of the subbands, including;

for each message element, selecting a group of neighboring coefficients in a subband, and modulating edge information in the neighboring coefficients to encode the message element; and

after embedding the message signal, inverse transforming the decomposed media signal into the perceptual domain.

2. The method of claim 1 wherein the media signal is an image.

3. The method of claim 1 including:

repeating the decomposing and embedding in segments of the media signal.

4. The method of claim 3 wherein the media signal is an image and the segments are blocks of image samples.

5. The method of claim 1 including:

embedding a watermark orientation signal into the media signal, which enables orientation of the message signal to be computed.

6. The method of claim 1 including:

in a subband at a first level of resolution, selecting N largest coefficients, where N is a predetermined number;

wherein selecting the group of coefficients for a message element includes selecting children coefficients of one of the N largest coefficients in a second higher level of resolution.

7. The method of claim 1 including:

embedding message elements in groups of neighboring coefficients throughout at least one subband.

8. The method of claim 7 including repeatedly embedding the message signal in two or more subbands.

9. The method of claim 1 wherein the message signal is a binary signal and the message elements have binary values.

10. The method of claim 9 wherein the message signal is spread spectrum modulated before embedding.

11. The method of claim 9 wherein the message signal is error correction encoded before embedding.

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

13. A method of decoding a message signal that has been embedded in a media signal such that the message signal is substantially imperceptible in a perceptual domain of the media signal, the method comprising:

decomposing the media signal from a perceptual domain to subbands, each subband including a set of coefficients within a frequency range;

decoding a message signal having two or more elements from at least one of the subbands, including;

for each message element, selecting a group of neighboring coefficients in a subband, and demodulating edge information in the neighboring coefficients to decode the message element.

14. The method of claim 13 wherein the media signal is an image.

15. The method of claim 13 wherein instances of the message signal are embedded in two or more subbands;

and including;

decoding each of the instances from the subbands;

comparing the instances with a reference to determine alteration of the media signal.

16. The method of claim 15 wherein the reference comprises an instance decoded from another subband of the media signal.

17. The method of claim 15 wherein a result of the comparison is output to a user to indicate alteration of the media signal.

18. The method of claim 15 wherein the result of the comparison is evaluated relative to a characterization of an alteration to detect a type of alteration.

19. The method of claim 18 wherein the type of alteration comprises compression of the media signal.

20. The method of claim 18 wherein the media signal is an image on a physical object and the type of alteration comprises copying of the physical object.

21. The method of claim 13 wherein the message signal includes a hash of the media signal.

22. The method of claim 21 wherein the hash comprises a hash computed of watermarked coefficients of one subband, and the hash is embedded in coefficients of a different subband.

23. The method of claim 22 including:

extracting the hash from the message signal and comparing it with a hash re-computed from the media signal.

24. A computer readable medium having software for performing the method of claim 13.

25. A watermark embedder for embedding auxiliary information in a media signal such that the auxiliary information is substantially imperceptible, the embedder comprising:

a wavelet transform operator for decomposing the media signal from a perceptual domain to subbands, each subband including a set of coefficients within a frequency range; and

a message encoder for embedding a message signal having two or more elements into at least one of the subbands, the embedder operable to modulate edge information in neighboring coefficients of a subband to encode the message elements.

26. The embedder of claim 25 wherein the message elements are embedded by modulating relative differences between neighboring coefficients.

27. A watermark decoder for decoding auxiliary information from a media signal in which the auxiliary information has been embedded so as to be substantially imperceptible in a perceptual domain of the media signal, the decoder comprising:

a wavelet transform operator for decomposing the media signal from a perceptual domain to subbands, each subband including a set of coefficients within a frequency range; and

a message decoder for decoding a message signal having two or more elements into at least one of the subbands, the decoder operable to demodulate edge information in neighboring coefficients of a subband to decode the message elements.

28. The decoder of claim 27 wherein the message elements are decoded by a demodulation operator that computes the relative differences between neighboring coefficients and estimating the message elements from the polarity computed by the demodulation operator.