Watermarking method and apparatus for compressed digital video

• US 5,809,139 A
• Filed: 09/13/1996
• Issued: 09/15/1998
• Est. Priority Date: 09/13/1996
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Vivo SA (Vivo Communication Technology Co. Ltd.)
• Inventors: Hartung, Frank H. D., Girod, Bernd
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/710,246
• Time in Patent Office: 732 Days
• Field of Search: 380/5, 380/20, 380/49, 380/23, 355/201, 382/232
• US Class Current: 380/202
• CPC Class Codes: G06T 1/0035 Output size adaptive watermarking
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: G06T 2201/0053 Embedding of the watermark in the coding stream, possibly without decoding; Embedding of the watermark in the compressed domain
• CPC Class Codes: H04N 19/00 Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 2005/91335 the copy protection signal being a watermark
• CPC Class Codes: H04N 21/23892 involving embedding information at multiplex stream level, e.g. embedding a watermark at packet level
• 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 5/913 for scrambling ; for copy protection

Abstract

A digital watermarking method and apparatus allows for the watermarking of a digital video signal in a compressed form, thereby allowing watermarking of a pre-compressed video sequence without requiring the decoding and re-coding of the signal. The watermark signal is a sequence of information bits which has been modulated by a pseudo-random noise sequence to spread it in the frequency domain. The video signal is transform coded, preferably with a discrete cosine transform, and a watermark signal, which has been transform coded using the same type of transform, is added to the coded video signal. The system also includes bitstream control to prevent an increase in the bit rate of the video signal. This allows the system to be used with transmission channels having strict bit rate constraints. For each transform coefficient of the video signal, the number of bits necessary to encode the watermarked coefficient is compared to the number of bits necessary to encode the unwatermarked coefficient. If more bits are required to transmit a watermarked coefficient than to transmit the corresponding unwatermarked coefficient, the watermarked coefficient is not output, and the unwatermarked coefficient is output in its place. When watermarking interframe coded data, a drift compensation signal may be used to compensate for the accumulating variations in the decoded video signal stored at the receiver. The system may also include an encryption/decryption capability, with the watermarking apparatus located at either the transmitting or receiving end of the transmission channel.

Claims

1. A method of embedding a watermark in a first portion of a digital video signal bitstream containing a digital video signal that has been processed using a hybrid interframe coder to transform the digital video signal into a plurality of video transform coefficients and code the video transform coefficients to a compressed video format, wherein the watermark comprises a predetermined sequence of information bits transformed into a plurality of watermark transform coefficients, the method comprising:

decoding the compressed video format to recover the plurality of video transform coefficients;

summing the watermark transform coefficients with the video transform coefficients to generate watermarked video coefficients; and

preventing drift in the first portion of the bitstream by compensating for artifacts resulting from previously added watermark transform coefficients.

2. A method according to claim 1 wherein the digital video signal is a digital video signal which has been processed using a hybrid interframe coder which is a MPEG-2 compatible coder.

3. A method according to claim 1 wherein preventing drift in the first portion of the bitstream comprises determining a difference signal indicative of the difference between a portion of the video transform coefficients before summing with the watermark transform coefficients and a corresponding portion of the watermarked video signal after summing with the watermark transform coefficients, and applying the difference signal to subsequent portions of the watermarked video coefficients.

4. A method according to claim 1 further comprising:

comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient; and

substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits is greater than said first number of data bits.

5. A method according to claim 1 further comprising:

comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient;

determining a reserve number of data bits, the reserve number being a difference between a total number of data bits used to represent a portion of the watermarked video coefficients already generated and a total number of data bits used to represent a portion of the video transform coefficients containing the same digital video information; and

substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits minus the reserve number of data bits is greater than said first number of data bits.

6. A method according to claim 1 further comprising encrypting the watermarked video coefficients.

7. A method according to claim 1 further comprising coding the watermarked video coefficients to a compressed watermarked video format.

8. A method according to claim 7 further comprising encrypting the compressed watermarked video coefficients.

9. A method according to claim 1 wherein summing the watermark transform coefficients with the video transform coefficients comprises summing watermark transform coefficients only with video transform coefficients which do not have a value of zero.

11. A method according to claim 1 wherein the watermark comprises a sequence of bits to which an error correcting code is added before being transformed to said watermark transform coefficients.

10. A method according to claim I wherein the compressed video format is an encrypted compressed video format and wherein the method further comprises decrypting the encrypted compressed video format prior to decoding the compressed video format.

12. A method of embedding a watermark in a first portion of a digital video signal bitstream containing a digital video signal that has been processed using a hybrid interframe coder to transform the digital video signal into a plurality of video transform coefficients and code the video transform coefficients to a compressed video format, wherein the watermark comprises a predetermined sequence of information bits transformed into a plurality of watermark transform coefficients, the method comprising:

decoding the compressed video format to recover the plurality of video transform coefficients;

summing the watermark transform coefficients with non-zero video transform coefficients to generate watermarked video coefficients;

preventing drift in the first portion of the bitstream by determining a difference signal indicative of the difference between a portion of the video transform coefficients before summing with the watermark transform coefficients and a corresponding portion of the watermarked video signal after summing with the watermark transform coefficients, and applying the difference signal to subsequent portions of the watermarked video signal; and

coding the watermarked video coefficients to a compressed watermarked video format.

13. A method according to claim 12 further comprising:

comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient; and

substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits is greater than said first number of data bits.

14. A method according to claim 12 further comprising:

comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient;

determining a reserve number of data bits, the reserve number being a difference between a total number of data bits used to represent a portion of the watermarked video coefficients already generated and a total number of data bits used to represent a portion of the video transform coefficients containing the same digital video information; and

substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits minus the reserve number of data bits is greater than said first number of data bits.

15. Apparatus for embedding a watermark in a first portion of a digital video signal bitstream containing a digital video signal that has been processed using a hybrid interframe coder to transfer the digital video signal into a plurality of video transform coefficients and code the video transform coefficients to a compressed video format, wherein the watermark comprises a predetermined sequence of information bits transformed into a plurality of watermark transform coefficients, the apparatus comprising:

a decoder for decoding the compressed video format so as to recover the plurality of video transform coefficients;

summing apparatus for summing the watermark transform coefficients with the video transform coefficients to generate watermarked video coefficients; and

a drift compensator to prevent drift in the first portion of the bitstream by compensating for artifacts resulting from previously added watermark transform coefficients.

16. Apparatus according to claim 15 wherein the digital video signal is one that was processed using a hybrid interframe coder which is a MPEG-2 compatible coder.

17. Apparatus according to claim 15 wherein the drift compensator further comprises:

means for determining a difference signal indicative of the difference between a portion of the video transform coefficients before summing with the watermark transform coefficients and a corresponding portion of the watermarked video signal after summing with the watermark transform coefficients; and

a summing node for summing the difference signal with subsequent portions of the watermarked video coefficients.

18. Apparatus according to claim 15 further comprising:

means for comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient; and

output selection apparatus for substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits is greater than said first number of data bits.

19. Apparatus according to claim 15 further comprising:

means for comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient;

means for determining a reserve number of data bits, the reserve number being a difference between a total number of data bits used to represent a portion of the watermarked video coefficients already output and a total number of data bits used to represent a portion of the video transform coefficients containing the same digital video information; and

output selection apparatus for substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits minus the reserve number of data bits is greater than said first number of data bits.

20. Apparatus according to claim 15 further comprising encryption apparatus for encrypting the watermarked video coefficients.

21. Apparatus according to claim 15 further comprising a coding apparatus which codes the watermarked video coefficients to a compressed watermarked video format.

22. Apparatus according to claim 21 further comprising encryption apparatus for encrypting the compressed watermarked video coefficients.

23. Apparatus according to claim 15 wherein the summing apparatus only sums watermark transform coefficients with video transform coefficients that do not have a value of zero.

24. Apparatus according to claim 15 wherein the compressed video format is an encrypted compressed video format and wherein the apparatus further comprises decryption apparatus for decrypting the encrypted compressed video format prior to decoding the compressed video format.

25. Apparatus according to claim 15 wherein the watermark comprises a sequence of bits to which an error correcting code is added before being transformed to said watermark transform coefficients.

26. A computer program product for embedding a watermark in a first portion of a digital video signal bitstream containing a digital video signal that has been processed using a hybrid interframe coder to transform the digital video signal into a plurality of video transform coefficients and code the video transform coefficients to a compressed video format, wherein the watermark comprises a predetermined sequence of information bits transformed into a plurality of watermark transform coefficients, the program code comprising;

program code for decoding the compressed video format to recover the plurality of video transform coefficients;

program code for summing the watermark transform coefficients with the video transform coefficients to generate watermarked video coefficients; and

program code for preventing drift in the first portion of the bitstream by compensating for artifacts resulting from previously added watermark transform coefficients.

27. A computer program product according to claim 26 wherein the digital video signal is a digital video signal which has been processed using a hybrid interframe coder which is a MPEG-2 compatible coder.

28. A computer program product according to claim 26 wherein the program code for preventing drift in the first portion of the bitstream comprises program code for determining a difference signal indicative of the difference between a portion of the video transform coefficients before summing with the watermark transform coefficients and a corresponding portion of the watermarked video signal after summing with the watermark transform coefficients, and applying the difference signal to subsequent portions of the watermarked video coefficients.

29. A computer program product according to claim 26 further comprising:

program code for comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient; and

program code for substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits is greater than said first number of data bits.

30. A computer program product according to claim 27 further comprising:

program code for comparing a first number of data bits necessary to represent a first one of said video transform coefficients to a second number of data bits necessary to represent a first one of said watermarked video coefficients which corresponds to the first video transform coefficient summed with a watermark transform coefficient;

program code for determining a reserve number of data bits, the reserve number being a difference between a total number of data bits used to represent a portion of the watermarked video coefficients already output and a total number of data bits used to represent a portion of the video transform coefficients containing the same digital video information; and

program code for substituting the first video transform coefficient for the first watermarked video coefficient if said second number of data bits minus the reserve number of data bits is greater than said first number of data bits.

31. A computer program product according to claim 26 further comprising program code for encrypting the watermarked video coefficients.

32. A computer program product according to claim 26 further comprising program code for coding the watermarked video coefficients to a compressed watermarked video format.

33. A computer program product according to claim 32 further comprising program code for encrypting the compressed watermarked video coefficients.

34. A computer program product according to claim 26 wherein the program code for summing the watermark transform coefficients with the video transform coefficients comprises program code for summing watermark transform coefficients only with video transform coefficients which do not have a value of zero.

35. A computer program product according to claim 26 wherein the compressed video format is an encrypted compressed video format and wherein the program code further comprises program code for decrypting the encrypted compressed video format prior to decoding the compressed video format.

36. A computer program product according to claim 26 wherein the watermark comprises a sequence of bits to which an error correcting code is added before being transformed to said watermark transform coefficients.