1 Department of Electrical Engineering, Stanford University Anne Aaron, Rui Zhang and Bernd Girod...

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Department of Electrical Engineering,Stanford University

Anne Aaron, Rui Zhang and Bernd Girod

Wyner-Ziv Coding of Motion Video

Aaron, Zhang, Girod: Wyner-Ziv Coding of Motion Video November 4, 2002

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Overview

Intraframe encoding with Interframe decoding

Wyner-Ziv Video Codec Simulation Results


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Interframe Video Compression

• Current video standards Interframe predictive

coding for compression Encoder is 5-10 times

more complex than decoder

X’i-1

Interframe Encoder

Interframe Decoder

Xi Xi’

Standard codec


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Intraframe Encoding – Interframe Decoding

Interframe Decoder

Intraframe EncoderXi

Xi-1’

Xi’

Proposed codecWyner-Ziv Coding

Side Information

• Dual SystemSimpler encoderPossibly complex

decoder


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Slepian-Wolf and Wyner-Ziv Coding

• Practical Codes Coset encoding

[Pradhan and Ramchandran, 1999] Trellis codes

[Wang and Orchard, 2001] Turbo codes

[Garcia-Frias and Zhao, 2001], [Bajcsy and Mitran, 2001] [Aaron and Girod, 2002]

LDPC codes [Liveris, Xiong, and Georghiades, 2002]

• Practical Applications [Pradhan and Ramchandran, 2001] [Liveris, Xiong, and Georghiades, 2002] [Jagmohan, Sehgal, and Ahuja, 2002]


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Wyner-Ziv Video Codec

Interframe Decoder

• Even frames are encoded independently• Odd frames are known as side information at the decoder

Scalar Quantizer

Turbo Encoder

Buffer

Even frameX

Intraframe Encoder

Turbo Decode

r

Request bits

Slepian-Wolf Codec

Interpolation

Reconstruction X’

Y

Odd frames

previous

next


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RCPT-Based Slepian-Wolf Codec

Y2iScalar

QuantizerTurbo

EncoderBuffer Turbo

Decoder

Request bits

Slepian-Wolf Codec

• Uniform scalar quantizer – no coset grouping• RCPT Slepian-Wolf Codec

Flexibility for varying statisticsEmbedded puncturing patternBit rate controlled by decoder through feedback

Decoded quantizedsymbols

Y

Even frameX


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Side Information

• Interpolation Average same block from previous and next frameMotion-compensated interpolation with symmetric motion

vectors• Flexibility in design for decoder • Statistics between side information and current frame

Laplacian residual modelEstimate the Laplacian parameter at the decoder

Interpolation

Y

Odd frames

previous

next


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Reconstruction Function

•Limits the magnitude of the reconstruction distortion

•Need dithering to avoid contouring

•Pixels reconstructed independently

Reconstruction X’

Y

Decoded quantizedsymbols


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Simulation

• Quantizer 2, 4, 16 levels

• Slepian-Wolf codec Rate 4/5 Turbo code Embedded puncturing pattern with period 8 Pe<10-3 ~ 25 pixels per frame

• Interpolation Averaging MC with symmetric motion vectors (SMV)

• Rate-PSNR Comparison with H263+ Intraframe coding Interframe coding (B frames) with no motion compensation Interframe coding (B frames) with motion compensation


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Carphone Sequence

6 dB

2 dB

8 dB


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Foreman Sequence

7 dB

4 dB

7 dB


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Foreman sequence

Side information SMV Interpolation

After Wyner-Ziv Coding16-level quantization (~1 bpp)


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Sample Frame

Side information SMV Interpolation



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Sample Frame

Side information Average Interpolation



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Carphone sequence

H263+ Intraframe Coding 410 kbps

Wyner-Ziv Codec SMV Interpolation

384 kbps


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Conclusion

• Use Wyner-Ziv coding for practical compression applicationUsed statistics of the source

• New video system Intraframe encoder – Interframe Decoder

• Compared to H263+2 to 7 dB better than Intraframe coding5 to 8 dB worse than Interframe coding with MC

• Further improvementsExploit spatial correlationAcceptable symbol error rate

1 Department of Electrical Engineering, Stanford University Anne Aaron, Rui Zhang and Bernd Girod...

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