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Video watermarking: applications and associated purpose Table |

Table 1 Video watermarking: applications and associated purpose Table |

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Everything starts when Hollywood studios release a new copyrighted DVD with CGMS bits encoding the message copy-never. Both CSS keys are stored on the lead-in area of the DVD. This area is only read by compliant players. This prevents factory-pressed legal disks from being displayed by noncompliant players. Moreover bit- for-bit illegal copies will contain CSS scrambled content, but not the keys. As a result, such illega copies cannot be displayed by any player, com- plant or not. If the output signal given by compliant players is digital, CGMS bits preven copying in the compliant world while 5C will avoid any communication with any noncompliant de- vices. However, to date, analog monitors are stil widespread and even compliant players output an analog signal for compatibility. Since CGMS bits do not survive digital to analog conversion, watermarking is introduced in order to avoid copying in the compliant world. Unfortunately, in the noncompliant world, APS only disables copy- ing of analog NTSC/PAL signals on VHS tapes. Disks without CSS or CGMS can then be easily generated e.g. thanks to a simple PC with a video capture card. Watermarking: The main purpose of water- marking is to provide a more secure solution than storing bits in the MPEG stream header. In DVD, digital watermarking is primarily intended for the CGMS bits and secondary for the APS bits.
Everything starts when Hollywood studios release a new copyrighted DVD with CGMS bits encoding the message copy-never. Both CSS keys are stored on the lead-in area of the DVD. This area is only read by compliant players. This prevents factory-pressed legal disks from being displayed by noncompliant players. Moreover bit- for-bit illegal copies will contain CSS scrambled content, but not the keys. As a result, such illega copies cannot be displayed by any player, com- plant or not. If the output signal given by compliant players is digital, CGMS bits preven copying in the compliant world while 5C will avoid any communication with any noncompliant de- vices. However, to date, analog monitors are stil widespread and even compliant players output an analog signal for compatibility. Since CGMS bits do not survive digital to analog conversion, watermarking is introduced in order to avoid copying in the compliant world. Unfortunately, in the noncompliant world, APS only disables copy- ing of analog NTSC/PAL signals on VHS tapes. Disks without CSS or CGMS can then be easily generated e.g. thanks to a simple PC with a video capture card. Watermarking: The main purpose of water- marking is to provide a more secure solution than storing bits in the MPEG stream header. In DVD, digital watermarking is primarily intended for the CGMS bits and secondary for the APS bits.
Fig. 2. Alternative watermarking strategies for video streaming.
Fig. 2. Alternative watermarking strategies for video streaming.
Fig. 3. Original and tampered video scenes.
Fig. 3. Original and tampered video scenes.
Examples of nonhostile video processings Table 2
Examples of nonhostile video processings Table 2
Fig. 4. Example of distortion created by a handled camera (exaggerated).
Fig. 4. Example of distortion created by a handled camera (exaggerated).
the reference pattern p, in the buffer with a two- dimensional cyclic convolution. Since such an operation is most efficiently computed in the frequency domain, this leads to Symmetrical Phase Only Matched Filtering (SPOMF) detection which is given by the following equation:
the reference pattern p, in the buffer with a two- dimensional cyclic convolution. Since such an operation is most efficiently computed in the frequency domain, this leads to Symmetrical Phase Only Matched Filtering (SPOMF) detection which is given by the following equation:
Pros and cons of the different approaches for video watermarking Table 3
Pros and cons of the different approaches for video watermarking Table 3
Fig. 6. Example of SPOMF detection. G. Doérr, J.-L. Dugelay | Signal Processing: Image Communication 18 (2003) 263-282
Fig. 6. Example of SPOMF detection. G. Doérr, J.-L. Dugelay | Signal Processing: Image Communication 18 (2003) 263-282
Fig. 7. Description of DEW embedding. where 6; is the DCT coefficient with index i in the zig-zag order in the bth DCT block, [.] indicates the prequantization with quality factor Qjpeg and c is a given cut-off index which was fixed to 27 in Fig. 7. The value of the embedded bit is encoded as the sign of the energy difference D = E, — Eg between the two regions A and B. All the energy after the cut-off index c in either region A or region B is eliminated by setting the corresponding DCT coefficients to zero to obtain the appropriate sign for the difference D. It should be noted that this can be easily done directly in the compressed domain by shifting the end of block (EOB) marker of the corresponding 8 x 8 DCT blocks toward the DC-coefficient up to the cut-off index. Finally, the inverse block DCT is computed and the shuffling is inversed in order to obtain the watermarked NE Ee OE Se ee Te eee The DEW method was initially designed for still images and has been extended to video by water- marking the I-frames of an MPEG stream [31]. It is based on selectively discarding high frequency DCT coefficients in the compressed data stream. The embedding process is depicted in Fig. 7. The 8 x 8 pixels blocks of the video frame are first pseudo randomly shuffled. This operation forms the secret key of the algorithm and it spatially randomizes the statistics of pixel blocks i.e. it breaks the correlation between neighbouring blocks. The obtained shuffled frame is then split into n 8 x 8 blocks. In Fig. 7, n is equal to 16. One
Fig. 7. Description of DEW embedding. where 6; is the DCT coefficient with index i in the zig-zag order in the bth DCT block, [.] indicates the prequantization with quality factor Qjpeg and c is a given cut-off index which was fixed to 27 in Fig. 7. The value of the embedded bit is encoded as the sign of the energy difference D = E, — Eg between the two regions A and B. All the energy after the cut-off index c in either region A or region B is eliminated by setting the corresponding DCT coefficients to zero to obtain the appropriate sign for the difference D. It should be noted that this can be easily done directly in the compressed domain by shifting the end of block (EOB) marker of the corresponding 8 x 8 DCT blocks toward the DC-coefficient up to the cut-off index. Finally, the inverse block DCT is computed and the shuffling is inversed in order to obtain the watermarked NE Ee OE Se ee Te eee The DEW method was initially designed for still images and has been extended to video by water- marking the I-frames of an MPEG stream [31]. It is based on selectively discarding high frequency DCT coefficients in the compressed data stream. The embedding process is depicted in Fig. 7. The 8 x 8 pixels blocks of the video frame are first pseudo randomly shuffled. This operation forms the secret key of the algorithm and it spatially randomizes the statistics of pixel blocks i.e. it breaks the correlation between neighbouring blocks. The obtained shuffled frame is then split into n 8 x 8 blocks. In Fig. 7, n is equal to 16. One
Fig. 8. Line scan of a video stream. The spreading operation permi ts to add redun- dancy by embedding one bit of information into cr samples of the video signal. The obtained sequence b(i) is then amplified locally factor A(i) >0 and modulated by by an adjustable a pseudo-random binary sequence p(i)¢ {—1, 1}. Finally, the spread spectrum watermark w(i) is added to the line- scanned video signal v(i), which gives the water- marked video signal v,,(i). The overall embedding process is consequently described by the following equation:
Fig. 8. Line scan of a video stream. The spreading operation permi ts to add redun- dancy by embedding one bit of information into cr samples of the video signal. The obtained sequence b(i) is then amplified locally factor A(i) >0 and modulated by by an adjustable a pseudo-random binary sequence p(i)¢ {—1, 1}. Finally, the spread spectrum watermark w(i) is added to the line- scanned video signal v(i), which gives the water- marked video signal v,,(i). The overall embedding process is consequently described by the following equation:
Related topics:
Computer SecurityCopyright ProtectionElectrical and Electronic EngineeringDigital WatermarkMultimedia Data
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