Xun Guo

Distributed Multi-view Video Coding

There are mainly two key points which can affect the efficiency of multi-view video capture and transmission system largely: communication between cameras and computing complexity of encoder. In this paper, we propose a practical framework of distributed multi-view video coding, in which inter-camera communication is avoided and the large computing complexity is moved from encoder to decoder. In this scheme, multi-camera video sources are encoded separately and decoded dependently, and the traditional inter frame is replaced by Wyner-Ziv frame. To reach this goal, Wyner-Ziv theory on source coding with side information is employed as the basic coding principle. A Wyner-Ziv coding method based on wavelet transform and turbo codes is used as the core of the scheme. To further improve the coding performance, we also consider exploiting the large redundancy between adjacent views. A more flexible prediction method that can jointly use temporal and view correlations is proposed to generate the side information at the decoder. The experimental results show that the coding performance of proposed DMVC scheme is very promising compared to the traditional intra coding.

Wyner–Ziv-Based Multiview Video Coding

Utilizing video correlations among views would definitely improve multiview video compression in terms of coding efficiency, which usually requests an expensive system to collect videos from different cameras and jointly compress them. Thanks to recent developments on distributed video coding, this paper proposes a new multiview video coding scheme based on Wyner-Ziv (WZ) coding technique, in which the complicated temporal and interview correlation exploration process is shifted from the encoder side to the decoder side so that broadband raw data traffic and high intensive computation for jointly encoding can be avoided. At the encoder side, a wavelet-based WZ scheme is proposed to compress video of every camera. Furthermore, in order to better utilize correlation in wavelet domain, all coefficients are organized as that done in SPIHT bit plane by bit plane. At the decoder side, a more flexible prediction technique that can jointly utilize temporal and view correlations is proposed to generate side information. Finally, experimental results show the proposed scheme significantly outperforms the conventional intra-frame coding for better random access and is even close to the inter-frame coding for better efficiency. Furthermore, compressed data is much robust when it is transmitted over an error-prone channel.

Inter-View Direct Mode for Multiview Video Coding

Global disparity between views is usually caused by the displacement between cameras, which can be accurately represented by a global geometric transformation. In this paper, we first propose an inter-view motion model in terms of the global geometric transformation to represent the motion correlation between two adjacent views. Specifically, the motion vector of a pixel in one view may be directly derived from that in another view according to the inter-view motion model. Further, we propose an inter-view direct mode to signal the decoder that the motion of a macroblock (MB) can be achieved from the coded view without any coding bits. The proposed inter-view direct mode is further incorporated in the existing multiview video coding (MVC) schemes (i.e., AVC-based MVC and 4-D wavelet-based MVC), working together with the other classical coding modes. The mode selection at each MB is accomplished with the rate-distortion optimization technique. The proposed inter-view direct mode can significantly reduce bits to code motion vectors especially at low bit rates, thus improving the coding efficiency

Distributed video coding using wavelet

This paper proposes a distributed video coding scheme based on the zero tree entropy (ZTE) coding. Wyner-Ziv theory on source coding with side information is taken as the basic coding principle, which makes independent encoding and joint decoding possible. In this scheme, wavelet transform is used to exploit the spatial correlation of a Wyner-Ziv frame. The quantized wavelet coefficients are reorganized in terms of the zero tree structure so as to identify the significant and insignificant coefficients. The significance map is intra-codec and transmitted. In particular, the significant coefficients are independently encoded with turbo coder, and only the parity bits are transmitted. At the decoder, a predictive frame generated through motion-compensated prediction is used as the side information, with which the Wyner-Ziv frame can be conditionally decoded. Experimental results show that, compared to the traditional intra-frame coding and pixel-domain Wnyer-Ziv video coding, the proposed scheme can achieve a better coding performance, especially at low bit rates

Free viewpoint switching in multi-view video streaming using Wyner-Ziv video coding

The free viewpoint switching is one of the most important features of multi-view video streaming. The key problem lies in how to achieve the best performance when the camera processing capability and the network bandwidth are limited. In this paper, we propose a novel free viewpoint switching scheme for multi-view video scenario, in which the distributed video coding technique is employed. In this scheme, the multi-camera video sources are encoded separately with the traditional hybrid video coding scheme, and meanwhile an alternative bitstream is produced for every frame based on the Wyner-Ziv coding method for the purpose of error correction when the viewpoint switching occurs. When switching happens, the Wyner-Ziv bits corresponding to the actual reference frame at the switching point is transmitted and used to recover the true reference. Instead of completely removing the mismatch, the proposed switching scheme tries to reduce the mismatch to an acceptable level so as to save the bits for the switching frame. A wavelet transform domain Wyner-Ziv coding method is proposed to produce the Wyner-Ziv bits for the switching frame. Conclusively, with the proposed scheme, the inter-camera communication can be avoided and the drifting error can be controlled efficiently when the viewpoint switching occurs.

An Optimal Non-Uniform Scalar Quantizer for Distributed Video Coding

In this paper, we propose a novel algorithm to design an optimal non-uniform scalar quantizer for distributed video coding, which aims at achieving a coding rate close to joint conditional entropy of the quantized video frames given the side information. Wyner-Ziv theory on source coding is employed as the basic coding principle and the asymmetric scenario is considered. In this algorithm, a probability distribution model, which considers the influence of the joint distribution of input source and side information to the coding performance, is established and used as the optimality condition firstly. Then, a modified Lloyd Max algorithm is used to design the scalar quantizer to give an optimal quantization for input source before coding. Experimental results show that compared to uniform scalar quantization, proposed algorithm can improve coding performance largely, especially at low bit rate

Multiview video coding based on global motion model

In this paper, we present a novel scheme for coding multiview video sequence based on global motion prediction between adjacent views. For that, the left-most view is compressed as reference sequence using standard block-based motion compensated prediction coding. And its right view is compressed with global motion prediction from the left view images. In the prediction, an eight-parameter global motion model is used to compute the global motion information between left and right-view images. Then the motion vectors of the right-view image are predicted from the left-view image based on the global information. To further reduce the coding complexity and improve coding efficiency, macroblock modes of current image are also predicted from the left-view image. H.264 coding scheme is employed as the baseline, in which Rate-Distortion Optimization is used to select the best coding mode. Experimental results show that, compared to coding multiview video sequence independently, the proposed scheme can save the bitrate up to 15%.

Viewpoint switching in multiview video streaming

In this paper, a novel coding scheme is proposed for switching viewpoint in multiview video streaming, which can switch freely and efficiently between any two adjacent views of the multiview video even if the switching point is not an intra frame. The proposed scheme implements the switch function at the predictive frames and improves the efficiency of the switched frames by limiting the mismatch between the references for the prediction and the reconstruction. Interview prediction, based on a global motion model, is used to reduce the differences between two adjacent views and the global disparity parameters are transmitted. To further improve the switching efficiency, a new rate-distortion optimization model is proposed to give the smart inter/intra selection when encoding. The H.264 coding scheme is employed as the platform. Experimental results show that, compared to switching directly, the proposed scheme can improve the coding efficiency up to 2 dB in PSNR.

Wyner-Ziv Video Coding Based on Set Partitioning in Hierarchical Tree

In this paper, we propose a Wyner-Ziv video coding scheme based on set-partitioning in hierarchical trees (SPIHT) which can utilizing not only the spatial and temporal correlations but also the high-order statistical correlations. Wyner-Ziv theory on source coding with side information is employed as the basic coding principle, which makes the independent encoding and joint decoding become possible. In the proposed scheme, wavelet transform is first used to de-correlate the spatial dependency of a Wyner-Ziv frame. Then the quantized transform coefficients are organized by using magnitude with a set partitioning sorting algorithm. The ordered bit planes are coded using the Wyner-Ziv coding based on turbo codes. At the decoder, side information generated by motion compensated interpolation is used to conditionally decode the Wyner-Ziv frame. Since the high order statistical correlation is used, the proposed algorithm owns advantages over the traditional pixel-domain and transform-domain Wyner-ziv video coding schemes.

Motion vector prediction in multiview video coding

In video coding, motion vectors always account for a large number of bits and affect coding efficiency largely. In this paper, we propose an efficient motion vector prediction algorithm for multiview video coding (MVC), which can predict motion vectors from adjacent views and achieve good prediction accuracy. We first investigate the correlations among different views and describe the disparity between adjacent views as global motion. The affine model is used to compute the global parameters between frames of adjacent views. At least one view is coded independently without interview prediction. After that, motion vectors of the frame to be coded can be derived from the motion vectors of the co-located coded frame in adjacent view using the global motion information. A rate-distortion optimization scheme is used to choose between the proposed method and traditional motion compensated prediction method. Experimental results show that, compared to simulcast coding, the proposed algorithm can achieve good performance and improve the coding efficiency up to 0.8 dB in PSNR.