Adaptive deblocking filter for transform domain Wyner?Ziv video coding

Wyner-Ziv (WZ) video coding is a particular case of distributed video coding, the recent video coding paradigm based on the Slepian-Wolf and Wyner-Ziv theorems that exploits the source correlation at the decoder and not at the encoder as in predictive video coding. Although many improvements have been done over the last years, the performance of the state-of-the-art WZ video codecs still did not reach the performance of state-of-the-art predictive video codecs, especially for high and complex motion video content. This is also true in terms of subjective image quality mainly because of a considerable amount of blocking artefacts present in the decoded WZ video frames. This paper proposes an adaptive deblocking filter to improve both the subjective and objective qualities of the WZ frames in a transform domain WZ video codec. The proposed filter is an adaptation of the advanced deblocking filter defined in the H.264/AVC (advanced video coding) standard to a WZ video codec. The results obtained confirm the subjective quality improvement and objective quality gains that can go up to 0.63 dB in the overall for sequences with high motion content when large group of pictures are used.     

Distributed video coding with adaptive two-step side information generation for smart and interactive media

Conventional video coding standards, such as MPEGx and H.26x, use a hybrid architecture of block-based motion compensation and discrete cosine transform (DCT) within the structure of a complex encoder and a simple decoder. Contrary to conventional video codecs, Wyner-Ziv (WZ) video coding, which is a practical application of distributed video coding (DVC) based on the Slepian-Wolf and WZ theorems, exploits the source correlation at the decoder, thereby allowing for the development of simpler encoders. However, the current WZ video coding algorithms cannot match the coding performance of conventional video coding. In order to improve the coding performance of transform-domain WZ video coding, an adaptive two-step side-information generation method is thus proposed for evaluation and analysis in this study. The proposed method uses decoded WZ frames in the down-sampled spatial resolution along with already decoded coefficients to successively improve rate-distortion (RD) performance as the decoding progresses. The experimental results show that the proposed method, compared to previous WZ video coding method, shows improved coding performance, particularly under critical conditions, such as cases with high motion content.     

基于高斯混合模型的Wyner-Ziv视频编码

针对现有Laplacian模型不能精确描述相关噪声分布,分布式视频编码(Distributed Video Coding,DVC)的率失真性能改善非常有限,文中提出一种基于高斯混合模型的分布式视频编码方法.首先分析了WZ帧与相应边信息之间相关噪声的统计特征,发现相关噪声信息的分布并不满足某种单峰分布,然后采用高斯混合模型(Gaussian Mixture Model,GMM)对噪声系数直方图进行拟合,提出基于样本特征的EM(Expectation Maximum)算法来估计模型参数.将提出的高斯混合相关噪声模型与相应的Laplacian模型进行比较,实验结果表明前者更能精确描述相关噪声的统计特征,基于该模型的DVC率失真性能优于基于Laplacian模型的DISCOVER方案,获得的平均增益接近1 dB.     

Decoder side information generation techniques in Wyner-Ziv video coding: a review

Multimedia Tools and Applications - In Wyner-Ziv (WZ) video coding, decoder side information (SI) takes a key role in a WZ video codec among other building blocks. In this paper, we review the...     

频率域Wyner-Ziv视频编码算法的改进

为提高分布式视频编码压缩率,依据无线传感网络终端设备及Wyner-Ziv视频编码特点,针对Bernd Girod的频域Wyner-Ziv视频编码方案提出改进算法。该算法在编码端通过简单DCT运算提出将图像块分为Skip模式、低频模式和全频模式三种可选模式,在解码端根据相应的编码模式分别选择平均插值、自适应搜索运动估计插值和自适应搜索精细运动估计插值的边信息估算方法联合解码。该算法既能通过消除大量的帧间预测与熵编码实现低码率传输,又能以最小的解码代价获得更精确的边信息,从而有效地避免图像解码质量下降。实验结果表明,在相同峰值信噪比情况下,该算法的码率比Bernd Girod提出的频域Wyner-Ziv算法平均下降40%。     

像素级运动矢量场边信息生成算法

在分布式视频编码（DVC）中,解码端生成的边信息的质量对整个系统的率失真(RD)性能有着重要影响。为了提高边信息的质量,进而提升DVC系统的RD性能,提出一种基于像素级运动矢量场的边信息生成算法(SGPMVF)。首先,通过运动估计分别获得前后两关键帧的像素级运动矢量场;然后,为Wyner-Ziv帧的每个像素选择合适的运动矢量;最后,通过帧间内插得到高质量的边信息。算法中提出基于SAD（绝对误差和）差值的搜索范围确定方法与像素级运动矢量选择方法。实验结果表明,对于快速运动的序列,该算法在不增加编码复杂度和码率的情况下使边信息的PSNR最大提高1.45 dB,并使DVC系统的RD性能提高0.3～0.7 dB。     

Transform domain distributed video coding with spatial correlations

Distributed Video Coding is a new coding technique which has been evolving very fast recently. However the rate distortion performances of current solutions are below the expectations especially for high motion sequences even at a group of picture (GOP) size of 2. Main reason of this problem is the temporal prediction of the Wyner-Ziv (WZ) frames at the decoder. In this paper we propose a novel transform domain DVC codec architecture which splits each frame into two sub-frames and they are encoded separately as key sub-frame and WZ sub-frame. Pixel interpolation or median prediction techniques are utilized to generate the side information at the decoder. Simulation results show that a significant rate distortion improvement can be obtained with the proposed algorithm over the current DVC solutions.     

基于多块模式决策的边信息生成方法

分布式视频编码中边信息的质量决定了系统的率失真性能,边信息质量越高,则率失真性能越好。针对视频序列中对象运动的不均匀特性,结合MCTI技术,本文提出了一种新的边信息生成算法。其基本思想是在编码端利用多块模式算法对帧中宏块进行划分,将宏块分为运动缓慢块和运动剧烈块;在解码端,对运动缓慢块直接由MCTI算法生成边信息,而运动剧烈块的边信息要经过后处理进行优化得到。仿真实验表明与直接由MCTI生成边信息方法相比,本文算法可以使生成边信息的峰值信噪比(PSNR)比原有的算法提高0.8dB-1.2dB左右,有效提高了边信息的质量。     

分布式视频编码中关键帧编码方式的改进

在分布式视频编码中关键帧间的时间相关性没有被利用, 据此提出一种基于频带划分的关键帧编码模式的选择方法。关键帧经过DCT后得到的系数带划分为低频带和高频带, 低频带部分采用Wyner-Ziv编解码, 然后对高频带进一步进行编码模式的选择, 分别进行Wyner-Ziv编解码和传统的帧内编解码, 且在解码端完成编码模式的选择, 通过反馈信道向编码端传送编码模式的选择。仿真结果表明, 在不增加编码端复杂度的情况下, 所提出的方法改善了解码后视频的质量, 使系统的峰值信噪比（PSNR）提高约1~5 dB。     

分布式视频编码中关键帧丢失错误保护

目的 分布式视频编码较其传统视频编码具有编码简单、误码鲁棒性高等特点,可以很好地满足如无人机航拍、无线监控等新型视频业务的需求。在分布式视频编码中,视频图像被交替分为关键帧和Wyner-Ziv帧,由于受到信道衰落和干扰等因素的影响,采用传统帧内编码方式的关键帧的误码鲁棒性远不如基于信道编码的Wyner-Ziv帧。关键帧能否正确传输和解码对于Wyner-Ziv帧能否正确解码起着决定性的作用,进而影响着整个系统的压缩效率和率失真性能。为此针对关键帧在异构网络中的鲁棒性传输问题,提出一种基于小波域的关键帧质量可分级保护传输方案。方法 在编码端对关键帧同时进行传统的帧内视频编码和基于小波域的Wyner-Ziv编码,解码端将经过错误隐藏后的误码关键帧作为基本层,Wyner-Ziv编码产生的校验信息码流作为增强层。为了提高系统的分层特性以便使系统的码率适应不同的网络条件,进一步将小波分解后图像的各个不同层的低频带和高频带组合成不同的增强层,根据不同信道环境,传输不同层的Wyner-Ziv校验数据。同时对误码情况下关键帧的虚拟噪声模型进行了改进,利用第1个增强层已解码重建的频带与其对应边信息来获得第2个和第3个增强层对应频带的更加符合实际的虚拟信道模型的估计。结果 针对不同的视频序列在关键帧误码率为1%20%时,相比较于传统的帧内错误隐藏算法,所提方案可以提高视频重建图像的主观质量和整体系统的率失真性能。例如在关键帧误码率为5%时,通过传输第1个增强层,不同的视频序列峰值信噪比（PSNR）提升可达25 dB左右;如果继续传输第2个增强层的校验信息,视频图像的PSNR也可以提升0.51.6 dB左右;如果3个增强层的校验信息都传输的话,基本上可以达到无误码情况下关键帧的PSNR。结论 本文所提方案可以很好地解决分布式视频编码系统中的关键帧在实际信道传输过程中可能出现的误码问题,同时采用的分层传输方案可以适应不同网络的信道情况。     

Toward fast Wyner-Ziv video decoding on multicore processors

The Wyner-Ziv video coding paradigm provides a framework where most of the complexity is moved from the encoder to the decoder. In this way, Wyner-Ziv coding efficiently supports multimedia services for mobile devices which have to capture, encode and send video. However, the complexity of the decoder is quite high and it should be reduced. This work presents several parallel Wyner-Ziv decoding algorithms aimed at reducing this high complexity. Considering the fact that technological advances provide us new hardware which supports parallel data processing, these algorithms efficiently distribute the burden of the complexity over the number of cores which are available in the architecture. Particularly four parallel approaches have been proposed and analyzed. In the first parallel approach, the each bitplane of a frame could be decoded in a parallel way by a different core, achieving a time reduction of 33.21 % in average, although it depends on the number of bitplanes used. The second approach proposes a spatial distribution of each frame, avoiding dependences between bitplanes and then obtaining a time reduction of 67 % in average. The third approach executes each GOP in a parallel way, avoiding all synchronization dependences and achieving 71 % of time reduction in average, although the maximum performance is reached when the key frame buffer is full. Finally, the last approach distributes the burden of complexity over two levels, namely GOP and frame, in order to obtain the advantages of both: a negligible rate distortion penalty based on the GOP approach, and a low delay introduced by the spatial distribution approach. By using this parallel approach, the decoding time is reduced up to 76 %. In addition, by using parallel decoding, 60 % of the energy consumption is saved. The proposed methods are scalable for any multicore processor architecture and adaptable for different Wyner-Ziv decoding schemes.     

An improved 3D wavelet-based scalable video coding codec for MC-EZBC

With the rapid growth of modern multimedia applications, 3D wavelet-based scalable video coding (SVC) codec has received considerable attention lately because of its high coding performance and flexibility in bitstream scalability. It combines the motion-compensated temporal filtering (MCTF) together with the spatial decomposition to produce an embedded bitstream offering various levels of video quality over the heterogeneous networks. However, in the existing 3D wavelet-based SVC schemes, where the block types for block matching algorithms are limited, weighting matrices for block-wise motion compensation are fixed, and variations in activities of temporal subbands are not considered in the selection of the Lagrange multiplier for mode decision. In this paper, our major contribution is to provide some recent extensions to the well-known scalable subband/wavelet video codec Motion-Compensated Embedded Zero Block Coding (MC-EZBC) using three novel and content adaptive algorithms. Firstly, the enhanced hierarchical variable size block matching (Enhanced HVSBM) algorithm is proposed for the variable block size motion estimation. Then, the rate-distortion optimization (RDO) based adaptive Lagrange multiplier selection model for mode decision is presented. Finally, we introduce the adaptive weighting matrices design for overlapped block motion compensation (OBMC). Experimental results show that all the three proposed algorithms significantly improve the overall coding performance of MC-EZBC. Comparisons with other popular wavelet-based SVC codecs demonstrate the effectiveness of our improved codec in terms of both video quality assessment and computational complexity.     

Wyner-Ziv视频编码中边信息估计改进算法

首先简要介绍了分布式编码基本原理和一种典型的分布式编码方案——Wyner-Ziv视频编码。然后在Wyner-Ziv视频编码中提出了一种改进边信息估计算法,该算法中运动估计采用加权MAD准则。实验仿真结果表明,采用该文算法得到的运动矢量场更为准确,同时在相同输出码率时PSNR比原始算法平均提高0.7 dB。     

Network-driven low complexity coding for wireless multi-view video system

For wireless multi-view video system, which has very limited capability for storage and computation at the encoder, it is essential to design a video coding scheme with low complexity. Wyner-Ziv (WZ) coding scheme shifts large computational complexities to decoder with side information reconstruction, however, its encoding efficiency is not high enough. To obtain higher encoding efficiency and lower encoding complexity for wireless multi-view video applications, a network-driven low complexity video coding method is proposed in the paper. The proposed method is designed to implement color correction, motion vector extrapolation and disparity extraction at the central node of network, so as to reduce large computational complexities of motion estimation at the encoder and disparity estimation at the decoder. Experimental results show that encoding efficiency of the proposed method is higher than those of WZ coding and H.264 intraframe coding methods. The encoding complexity of the proposed method is greatly decreased and the decoded views are of color consistency, which is favorable to high quality view rendering at the decoder.     

多解析度自适应零块判决算法

在视频会议等应用中,视频编码的速度是保证系统实时性的关键.为了减小视频编码的运算量并提高系统的整体性能,提出了多解析度的自适应零块发现判决算法.多解析度通过对图像的子采样从而大幅度降低了搜索最佳匹配块的次数;而自适应的零块判决算法使得运动搜索速度收敛的更快,在不影响图像质量的前提下提高了编码的效率,并且减少了后续模块(DCT、量化等)所占用的时间.利用H.263算法进行了测试,结果显示在图像主客观质量基本不变的前提下,编码时间最多减少了近40%.     

面向多媒体传感器网络的视频压缩新算法

视频压缩可以降低多媒体传感器网络中的数据信息量。传统分布式视频编码方案采用区域统一编码,可能导致运动剧烈区域解码估计的失真。提出一种改进的分布式视频编码算法。该算法基于图像梯度场,针对Wyner-Ziv帧不能准确编解码的区域,通过ROI判定准则提取该区域并基于熵编码压缩,图像其他区域则基于LDPC实现分布式编解码,进而实现视频的优化传输。仿真实验表明：本文算法可增强运动剧烈区域的编码效率,在降低码率的同时提高解码图像质量,最终降低传感器节点能耗。     

基于边信息的分布式视频压缩感知重建

WZ视频编码系统中的虚拟信道会因信道模型参数估计的不稳定导致系统性能下降,为了克服该问题,提出不带有虚拟信道的分布式视频压缩感知重建算法,仅靠解码端获得的压缩感知观测值对非关键帧的错误进行纠正,并利用平滑投影Landweber迭代求解联合重建模型.实验证明本文所提出算法获得了更好的率失真性能和更低的重建时间.     

Motion vector refinement in a Wyner--Ziv to H.264 transcoder for mobile telephony

The authors develop a decoder/encoder system (transcoder) to solve the consumption constraint in the communications between end-user devices, when a new Wyner?Ziv (WZ)/H.264 framework is defined for being used in mobile-to-mobile environments. This approach is based on leaving to the devices only WZ video encoding and traditional video decoding; the lowest complexity algorithms in both paradigms. The system shifts the burden of complexity to the network, where an improved transcoder that reuses information between both paradigms is allocated. The WZ decoding motion vectors are used to reduce the H.264 motion estimation process. The proposed transcoder offers a complexity reduction up to 60% on average, without any rate distortion drop.     

一种基于3DTV编解码技术的视频流传输方法*

3DTV编解码技术及其立体视频流的优化传输方法是构建实时立体多视角3DTV系统的关键所在。通过对立体视频压缩编码和优化技术、立体视频解码技术,以及运动补偿预测与视差补偿预测技术的分析,在基于DSP平台TMS320DM642上进行AVS标清立体视频编解码及视频流优化传输,得出将互补的流媒体内容分发技术加以融合的立体视频流传输方法。     

In‐band scalable video coding with integrated wavelet‐based display driving

Abstract— The increasing demand for multimedia over networks and the heterogeneous nature of today's networks and playback devices impose the stringent need for scalable video coding. In this context, in‐band wavelet‐based video‐coding architectures offer full scalability in terms of quality, resolution, and frame‐rate and provide compression performance competitive with that of state‐of‐the‐art non‐scalable technology. Despite these advances, video streaming over wireless networks to handheld terminals is lagging in popularity due to the high power consumption of the existing portable devices. As a possible approach to alleviate this problem, the integration of wavelet‐based passive‐matrix‐display driving into the inverse discrete wavelet transform (IDWT) block of the in‐band video decoding architecture was investigated. In a nutshell, the IDWT no longer needs to be performed by the decoder, being synthesized instead by the display itself. This integration reduces the number of calculations required to generate the driving waveforms for passive‐matrix displays and inherently leads to reduced power consumption on portable terminals. Moreover, the wavelet transform and the considered video‐codec architecture are both resolution‐scalable. Hence, the resolution‐scalability feature of the video codec, enabling resolution‐scalable display driving, is another means to control the power consumption of the portable device.