Methods and apparatus for enhancing the robustness of watermark extraction from digital host content

• US 20060239502A1
• Filed: 04/26/2005
• Published: 10/26/2006
• Est. Priority Date: 04/26/2005
• Status: Active Grant

• Current Assignee: IP Acquisitions, LLC
• Original Assignee: Verance Corporation
• Inventors: Petrovic, Rade, Winograd, Joseph M., Jemili, Kanaan, Tehranchi, Babak
• Granted Patent: US 7,616,776 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0071 using multiple or alternating watermarks
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: H04L 2209/608 Watermarking
• CPC Class Codes: H04L 9/088 Usage controlling of secret information, e.g. techniques for restricting cryptographic keys to pre-authorized uses, different access levels, validity of crypto-period, different key- or password length, or different strong and weak cryptographic algorithms network architectures or network communication protocols for using time-dependent keys in a packet data network H04L63/068
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32245 Random or pseudorandom selection of pixels
• CPC Class Codes: H04N 1/32299 using more than one embedding method
• CPC Class Codes: H04N 1/32315 Selecting a particular method from amongst a plurality of methods
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark

Abstract

Methods and apparatus for enhancing the robustness of watermark extraction from digital host content are provided. Embedded watermarks may be extracted from received digital host content in accordance with a stego key. A first watermark is extracted and a number of errors in the first extracted watermark is assessed. If the number of errors is above a first pre-determined value, at least a second watermark is extracted from the host content. A number of errors in at least the second extracted watermark is assessed. If the number of errors in at least the second extracted watermark is above a second pre-determined value, the extraction results for the extracted watermarks are combined in order to cumulatively assess the validity of the first extracted watermark and at least the second extracted watermark.

Claims

1. A method for enhancing the robustness of watermark extraction from digital host content, comprising:

receiving a digital host content;

extracting embedded watermarks from said host content in accordance with a stego key, said extracting comprising;

(a) extracting a first watermark;

(b) assessing a number of errors in the first extracted watermark; and

if the number of errors is above a first pre-determined value;

(c) extracting at least a second watermark;

(d) assessing a number of errors in at least the second extracted watermark; and

if the number of errors in at least the second extracted watermark is above a second pre-determined value, combining the extraction results of steps (a) and (c) to cumulatively assess the validity of the first extracted watermark and at least the second extracted watermark.

2. The method of claim 1, wherein said combining comprises:

assigning weights to the first and at least the second extracted watermarks;

adding the weights assigned to the first and at least the second extracted watermarks to obtain an accumulated weight value; and

comparing the accumulated weight value to at least a first pre-defined reference value to assess the validity of the extracted watermarks.

3. The method of claim 2, wherein the assigning of the weights are adapted in accordance with soft decision information.

4. The method of claim 3, wherein said soft decision information comprises probability values.

5. The method of claim 1, wherein the first and at least the second extracted watermarks are separated by a pre-determined interval.

6. The method of claim 5, wherein said pre-determined interval is a function of the duration of the embedded watermarks.

7. The method of claim 6, wherein said separation is a multiple of the duration of the embedded watermarks.

8. The method of claim 1, wherein said combining occurs only if the number of errors in at least the second extracted watermark does not exceed a third pre-determined value.

9. The method of claim 8, wherein said third pre-determined value is selected in accordance with at least one of a desired robustness, computational efficiency or false positive rate of the extraction.

10. The method of claim 1, wherein the number of errors in the first and at least the second extracted watermarks are obtained by comparing the detected watermark symbols to a pre-defined template.

11. The method of claim 1, wherein the number of errors in the first and at least the second extracted watermarks are estimated by decoding watermark packets that are Error-Correction-Code encoded.

12. The method of claim 1, wherein the first and the second pre-determined values are determined in accordance with at least one of a desired robustness, computational efficiency, or false positive rate of the extraction.

13. The method of claim 1, further comprising:

extracting at least a third detected embedded watermark prior to said combining, assessing the number of errors in at least the third extracted watermark; and

if the number of errors is above a third pre-determined value;

averaging symbols of the first, second and at least the third extracted watermarks to produce a composite watermark packet; and

measuring the number of errors in the composite watermark packet to assess the validity of embedded watermarks.

14. The method of claim 13, wherein said averaging is adapted in accordance with soft decision information.

15. The method of claim 14, wherein said soft decision information comprises probability values associated with individual bits of the first, second and at least the third extracted watermark.

16. Apparatus for enhancing the robustness of watermark extraction from digital host content, comprising:

a receiver for receiving a digital host content;

extraction means for extracting embedded watermarks from said host content in accordance with a stego key, said extracting means;

(a) extracting a first watermark;

(b) assessing a number of errors in the first extracted watermark; and

if the number of errors is above a first pre-determined value;

(c) extracting at least a second watermark;

(d) assessing a number of errors in at least the second extracted watermark; and

if the number of errors in at least the second extracted watermark is above a second pre-determined value, combining means for combining the extraction results of steps (a) and (c) to cumulatively assess the validity of the first extracted watermark and at least the second extracted watermark.

17. A method for enhancing the robustness of watermark extraction from digital host content, comprising:

receiving a digital host content;

extracting embedded watermarks from the host content in accordance with at least one stego key, said extracting of said embedded watermarks comprising;

(a) decoding individual symbols of an embedded watermark in accordance with at least one watermark detection algorithm;

(b) assigning discrete symbol values to said decoded symbols;

(c) generating likelihood measures associated with said decoded symbols; and

(d) assessing the validity of said extracted watermarks in accordance with said discrete symbol values and likelihood measures.

18. The method of claim 17, wherein said likelihood measures comprise probability values.

19. The method of claim 17, wherein the assessing of said validity of said extracted watermarks comprises:

producing weighted watermark symbols by multiplying each discrete symbol value by the likelihood measure corresponding to said symbol value;

arranging said weighted watermark symbols in a pre-defined order to form a weighted watermark packet;

comparing the number of errors in said weighted watermark packet to a pre-determined reference value.

20. The method of claim 17, wherein the likelihood measures are obtained in accordance with a set of pre-defined threshold values.

21. The method of claim 20, wherein the likelihood measures are generated in accordance with a distance between the decoded symbols and said threshold values.

22. The method of claim 17, wherein the detection algorithm comprises at least one of spread spectrum, autocorrelation modulation, peak amplitude modulation, or replica modulation techniques.

23. The method of claim 17, wherein subsequent to the receiving of host content, at least one boundary of the embedded watermarks is estimated by detecting a presence of a synchronization pattern embedded in the host content.

24. The method of claim 23, wherein said detecting of said synchronization pattern comprises:

(a) decoding individual bits of an embedded pattern in accordance with at least one watermark detection algorithm;

(b) assigning discrete bit values to decoded bits of the embedded pattern;

(c) generating likelihood measures associated with extracted bits of the embedded pattern; and

(d) assessing a presence of the synchronization pattern in accordance with said bit values and associated likelihood measures.

25. Apparatus for enhancing the robustness of watermark extraction from digital host content, comprising:

a receiver for receiving a digital host content;

extracting means for extracting embedded watermarks from the host content in accordance with at least one stego key, said extracting means adapted for;

(a) decoding individual symbols of an embedded watermark in accordance with at least one watermark detection algorithm;

(b) assigning discrete symbol values to said decoded symbols;

(c) generating likelihood measures associated with said decoded symbols; and

(d) assessing the validity of said extracted watermarks in accordance with said discrete symbol values and likelihood measures.