Method and apparatus for providing an asymmetric watermark carrier
A low-frequency, temporally asymmetric watermark carrier decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner. This allows the carrier to be embedded, e.g., in a video work, in a manner that renders the resultant watermark virtually invisible to the human eye. Moreover, the resultant watermark is substantially resistant to common pirating techniques in which high-frequency visual content (e.g., including watermark data) tends to be filtered out by piracy processing.
1. A method for inserting watermark data into a data stream, the method comprising the steps of:
selecting a location in said data stream for inserting said watermark data; and
applying a temporally asymmetric watermark carrier to the selected location, wherein said temporally asymmetric watermark carrier decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner.
2. The method of claim 1 , wherein said temporally asymmetric watermark carrier is a positive carrier.
3. The method of claim 2 , wherein said temporally asymmetric watermark carrier comprises:
an onset following a substantially Gaussian function; and
a decay substantially following a raised cosine function.
4. The method of claim 1 , wherein said temporally asymmetric watermark carrier is a negative carrier.
5. The method of claim 4 , where in said temporally asymmetric watermark carrier comprises:
an onset substantially following a raised cosine function; and a decay following a substantially Gaussian function.
6. The method of claim 1 , wherein said temporally asymmetric watermark carrier is a low-frequency carrier.
7. The method of claim 1 , wherein said temporally asymmetric watermark carrier is embodied as a substantially smooth curve representing luminance over time.
8. The method of claim 1 wherein a standard deviation of said temporally asymmetric watermark carrier is thirty frames of a video stream contained in said data stream.
9. The method of claim 1 , wherein said temporally asymmetric watermark carrier is at least partially dithered.
10. A computer readable medium containing an executable program for inserting watermark data into a data stream, where the program performs the steps of:
selecting a location in said data stream for inserting said watermark data; and
applying a temporally asymmetric watermark carrier to the selected location, wherein said temporally asymmetric watermark carrier decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner.
11. The computer readable medium of claim 10 , wherein said temporally asymmetric watermark carrier is a positive carrier.
12. The computer readable medium of claim 11 , wherein said temporally asymmetric watermark carrier comprises:
an onset following a substantially Gaussian function; and
a decay substantially following a raised cosine function.
13. The computer readable medium of claim 10 , wherein said temporally asymmetric watermark carrier is a negative carrier.
14. The computer readable medium of claim 13 , wherein said temporally asymmetric watermark carrier comprises:
an onset substantially following a raised cosine function; and
a decay following a substantially Gaussian function.
15. The computer readable medium of claim 10 , wherein said temporally asymmetric watermark carrier is a low-frequency carrier.
16. The computer readable medium of claim 10 , wherein said temporally asymmetric watermark carrier is embodied as a substantially smooth curve representing luminance over time.
17. The computer readable medium of claim 10 , wherein a standard deviation of said temporally asymmetric watermark carrier is thirty frames of a video stream contained in said data stream.
18. The computer readable medium of claim 10 , wherein said temporally asymmetric watermark carrier is at least partially dithered.
19. A watermarked data stream generated by:
selecting a location in said data stream for encoding watermark data; and
applying a temporally asymmetric watermark carrier to the selected location, wherein said temporally asymmetric watermark carrier monotonically decreases in luminance more slowly than it monotonically increases in luminance.
20. A method for detecting a watermark carrier in a data stream, said method comprising the steps of:
determining the location of said watermark carrier, wherein said watermark carrier is a temporally asymmetric watermark carrier that decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner;
calculating a first normalized correlation for a positive version of said temporally asymmetric watermark carrier;
calculating a second normalized correlation for a negative version of said temporally asymmetric watermark carrier; and
analyzing said first and second normalized correlations to determine whether a watermark is present in said data stream.
21. The method of claim 20 , wherein said analyzing step comprises the steps of:
determining which of said first and second normalized correlations has a positive value and which of said first and second normalized correlations has a negative value;
determining whether the normalized correlation having the positive value has a greater magnitude than the normalized correlation having the negative value; and
concluding that a watermark carrier present in said data stream corresponds to the version of said temporally asymmetric watermark carrier that corresponds to the normalized correlation having the positive value.
22. A computer readable medium containing an executable program for detecting a watermark carrier in a data stream, where the program performs the steps of:
determining the location of said watermark carrier, wherein said watermark carrier is a temporally asymmetric watermark carrier that decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner;
calculating a first normalized correlation for a positive version of said temporally asymmetric watermark carrier;
calculating a second normalized correlation for a negative version of said temporally asymmetric watermark carrier;
analyzing said first and second normalized correlations to determine whether a watermark is present in said data stream.
23. Apparatus for inserting watermark data into a data stream, the apparatus comprising:
means for selecting a location in said data stream for inserting said watermark data; and
means for applying a temporally asymmetric watermark carrier to the selected location, wherein said temporally asymmetric watermark carrier decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner.
24. Apparatus for detecting a watermark carrier in a data stream, said apparatus comprising:
means for determining the location of said watermark carrier, wherein said watermark carrier is a temporally asymmetric watermark carrier that decreases in luminance in a substantially monotonic manner more slowly than it increases in luminance in a substantially monotonic manner;
means for calculating a first normalized correlation for a positive version of said temporally asymmetric watermark carrier;
means for calculating a second normalized correlation for a negative version of said temporally asymmetric watermark carrier; and
means for analyzing said first and second normalized correlations to determine whether a watermark is present in said data stream.