Transform-domain Wyner-Ziv Codec for Video

1

Department of Electrical Engineering,Stanford University

Anne Aaron, Shantanu Rane, Eric Setton and Bernd Girod

Transform-domain Wyner-Ziv Codec for Video

Aaron, et al: Transform-domain Wyner-Ziv Codec for Video Jan. 21, 2004 2

Overview

Low-complexity video encoding Transform-domain Wyner-Ziv video codec Simulation results


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


Low-complexity Video Coding

Interframe Decoder

Intraframe EncoderXi

Xi-1’

Xi’

Proposed codec

Wyner-Ziv Coding Lossy source coding with decoder side information

Side Information

• Low-complexity encoding, possibly more complex decoding

• Applications: video sensors for surveillance, wireless PC cameras, mobile camera phones

Similar work: [Puri and Ramachandran, Allerton 2002, ICASSP 2003, ICIP 2003]


Distributed Source Coding

Encoder

Encoder

X

Y

Decoder YX ,

XR

YR

Statistically dependent

)|(

)|(

),(

XYHR

YXHR

YXHRR

Y

X

YX

Slepian-Wolf Theorem

EncoderX

Y

Decoder

X

)(| dRWZYX

)()( || dRdR YXWZ

YX Wyner-Ziv Theorem

Statistically dependent


Wyner-Ziv Pixel Video Codec

Interframe Decoder

Scalar Quantizer

Turbo Encoder Buffer

WZ frames

W

Intraframe Encoder

Turbo Decode

r

Request bits

Slepian-Wolf Codec

Interpolation/

Extrapolation

Reconstruction

Y

Key frames

K Conventional Intraframe coding

Conventional Intraframe decoding

W’

K’

[Aaron, Zhang, and Girod, Asilomar 2002][Aaron, Rane, Zhang, and Girod, DCC 2003][Aaron, Setton and Girod, ICIP 2003]

Side information


Wyner-Ziv DCT Video Codec

WZ frames

W

Request bits

Interpolation/ Extrapolation

Reconstruction

Key framesK Conventional

Intraframe coding

Conventional Intraframe decoding

DCT

For each transform band k

K’

W’

Y

Yk

Xk Xk’

IDCT

Decoded WZ frames

level Quantizer

DCT

kM2 Turbo Encoder

BufferTurbo

DecoderExtract bit-

planes

qk

bit-plane 1

bit-plane 2

bit-plane Mk

…

qk’

Interframe Decoder

Intraframe Encoder

level Quantizer

DCT

kM2 Turbo Encoder

BufferTurbo

DecoderExtract bit-

planes


Side information


• Each coefficient band is quantized using a scalar quantizer with levels.

Quantizers

kM2

64 32 16 8

32 16 8 4

16 8 4 4

8 4 4 1

32 16 8 4

16 8 4 4

8 4 4 1

4 4 1 1

32 8 4 1

8 4 1 1

4 1 1 1

1 1 1 1

16 8 1 1

8 1 1 1

1 1 1 1

1 1 1 1

level Quantizer

WZ frameW

4x4 DCT

XkkM2 qk

For each transform band k

256} ..., 4, 2, {1,2 kM

• Combination of quantizers determines the bit allocation across bands.

Mk = number of bit planes for kth coefficient band

DC band

Sample quantizers: Values represent number quantization levels for coefficient band

Highest freq AC band


RCPT-based Slepian-Wolf Codec

Turbo Encoder

BufferTurbo

DecoderRequest bits

Extract bit-planes

bit-plane 1

bit-plane 2

bit-plane Mk

… qk’qk

Yk

• Bit planes of coefficients are encoded independently but decoded successively

• Rate-compatible punctured turbo code (RCPT)Flexibility for varying statisticsBit rate controlled by decoder through feedback

• Turbo decoder can perform joint-source channel decoding


Flexible Side Information


Y

Decoded frames

Side information• To generate side information

Interpolation or extrapolationWith or without motion-compensation (MC)

• Flexibility in design for decoder • Laplacian residual model between transform

coefficients of side information and of current frame. Different Laplacian parameter for each coefficient band.


2 dB

11 dB

Compression Performance

• Mother and Daughter QCIF sequence

• Alternating key frames and Wyner-Ziv frames (K-W-K-W)

• Slepian-Wolf codec: Rate 4/5 Turbo code

• Side information – MC-Interpolation MC-Extrapolation


3 dB

8 dB

Compression Performance

• Foreman QCIF sequence

• Alternating key frames and Wyner-Ziv frames (K-W-K-W)

• Slepian-Wolf codec: Rate 4/5 Turbo code

• Side information – MC-Interpolation MC-Extrapolation


Low-Complexity Side Information

• To decrease complexity in generating side information Average Interpolation Previous frame copy

• For low-motion sequences, minimal performance degradation

• Transform-domain codec





Side information Average Interpolation

After Wyner-Ziv Coding 370 kbps


H263+Intra vs WZ Codec

H263+ Intraframe Coding 330 kbps, 32.9 dB

Wyner-Ziv Codec 274 kbps, 39.0 dB

WZ codec: Transfor-domain, side information using MC-Interpolation. Only WZ-frames shown


H263+ I-B-I-B 145 kbps, 40.4 dB

Wyner-Ziv Codec 156 kbps, 37.5 dB

H263+Inter vs WZ Codec

WZ codec: Transfor-domain, side information using MC-Interpolation. Only WZ-frames shown


Conclusion

• A new video compression system with intraframe encoding but interframe decoding

• Low-complexity encoding for applications such as mobile camera phones and video surveillance networks, wireless PC cameras

• Transform-domain codec performs up to 2 dB better than pixel-domain scheme

• Compared to H.263+Up to 11 dB better than Intraframe codingPerformance gap from H.263+ interframe coding

Documents

Transform-domain Wyner-Ziv Codec for Video