Synchronization of digital watermarks

• US 20050185819A1
• Filed: 01/20/2005
• Published: 08/25/2005
• Est. Priority Date: 01/22/2002
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Delp, Edward J., Lin, Eugene T.
• Granted Patent: US 7,840,005 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• 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 21/242 Synchronization processes, e.g. processing of PCR [Program Clock References] arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/4302 Content synchronisation processes, e.g. decoder synchronisation
• CPC Class Codes: H04N 21/44008 involving operations for analysing video streams, e.g. detecting features or characteristics in the video stream arrangements characterised by components specially adapted for monitoring, identification or recognition of video in broadcast systems H04H60/59
• 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
• CPC Class Codes: H04N 5/04 Synchronising for television systems using pulse code modulation H04N7/56

Abstract

A method for synchronization of a digital watermark generates a digital watermark based on feature extraction and a key generator. The synchronization method is adapted for both temporal and spatial synchronization. Statistical features of the watermarked signal along with key generators are used to compute keys used to detect embedded digital watermarks that vary over time or space. For spatial synchronization, spatial redundancy is used to detect geometric distortion of a signal in which the watermark is embedded using an autocorrelation method to detect peaks caused by the redundancy of the watermark structure. These peaks are then analyzed with a histogram method to detect rotation and scaling of the host media signal. The spatial synchronization process is applied to watermarks for both intra-coded frames of video (I-frames) as well as still images.

Claims

1. A method for spatial synchronization of a digital watermark, the method comprising:

detecting peaks due to spatial redundancy of the digital watermark in a host media signal;

analyzing the peaks to derive estimates of geometric distortion of the host media signal;

computing a histogram of the estimated geometric distortion parameters; and

from the histogram, computing a geometric distortion of the host media signal.

2. The method of claim 1 wherein the geometric distortion parameters represent rotation angles.

3. The method of claim 1 wherein the geometric distortion parameter represent spatial scaling.

4. The method of claim 1 wherein the spatial redundancy is controlled via a state machine that repeats a portion of a watermark structure, and varies another portion of the watermark structure over a spatial coordinate system of the host media signal.

5. A method for embedding a digital watermark that is robust to geometric distortion comprising:

using a state machine to generate a watermark structure corresponding to a spatial coordinate system of a host media signal, the state machine introducing spatial redundancy used for spatial synchronization of the digital watermark, wherein the spatial redundancy is controlled via that state machine such that a portion of the watermark structure is repeated, and portion of the watermark structure is varied over the spatial coordinate system of the host media signal; and

modifying the host media signal to embed the watermark structure in the host media signal.

6. The method of claim 5 wherein the state machine is dependent on a key with random properties.

7. The method of claim 5 wherein the state machine is dependent on a feature of the host media signal.

8. A method of synchronization of a digital watermark detector comprising:

receiving a host media signal in which a digital watermark is embedded;

calculating a content feature from the host media signal; and

using the content feature as a key to detect the digital watermark.

9. The method of claim 8 including using the content feature to perform temporal synchronization of the digital watermark.

10. The method of claim 9 including using the content feature to perform temporal synchronization of the digital watermark in frames of video.

11. The method of claim 8 wherein the content feature comprises statistical features of blocks of the host media signal.

12. The method of claim 11 wherein the statistical characteristics comprise averages of data values in blocks of the host media signal.

13. The method of claim 8 including:

using the content feature to identify locations in the host media signal in which to perform watermark detection operations.

14. The method of claim 13 wherein the watermark detection operations comprise a search for the digital watermark.

15. The method of claim 8 wherein the digital watermark is embedded by quantizing features of the host media signal.

16. The method of claim 8 wherein the content feature is input to a function that generates the key.

17. The method of claim 16 wherein the function comprises a state machine.

18. The method of claim 16 wherein the function identifies attributes of the digital watermark that vary over time or space.

19. The method of claim 16 wherein the function provides a pseudorandom map of the digital watermark.

20. The method of claim 8 wherein the key is used to identify temporal locations of a digital watermark, and the digital watermark varies over time according a pseudorandom function.