Improved side information generation algorithm for Wyner-Ziv video coding简

Side information has a significant influence on the rate-distortion（RD） performance of distributed video coding（DVC）. In the conventional motion compensated frame interpolation scheme, all blocks adopt the same side-information generation method regardless of the motion intensity inequality at different regions. In this paper, an improved method is proposed. The image blocks are classified into two modes, fast motion and slow motion, by simply computing the discrete cosine transformation（DCT） coefficients at the encoder. On the decoder, it chooses the direct interpolation and refined motion compensated interpolation correspondingly to generate side information. Experimental results show that the proposed method, without increasing the encoder complexity, can increase the average peak signal-to-noise ratio（PSNR） by up to 1~ 2 dB compared with the existing algorithm. Meanwhile, the proposed algorithm significantly improves the subjective quality of the side information.     

Wyner-Ziv视频编码中边信息生成算法研究

在Wyner-Ziv视频编码系统中,针对生成边信息容易出现块效应和重影现象的问题,提出了一种基于原始图像相关性的重叠块双向运动补偿算法.在编码端计算原始图像相关性,并将相关性数据发送到解码端辅助运动估计,得到较精确的运动矢量,最后通过重叠块双向运动补偿生成边信息.实验结果表明,与现有的双向运动补偿内插算法相比,提出的算法生成边信息的平均PSNR可以提高1.5~3dB,且边信息的主观质量也有明显改善.     

Perceptual-based distributed video coding

In this paper, we propose a perceptual-based distributed video coding (DVC) technique. Unlike traditional video codecs, DVC applies video prediction process at the decoder side using previously received frames. The predicted video frames (i.e., side information) contain prediction errors. The encoder then transmits error-correcting parity bits to the decoder to reconstruct the video frames from side information. However, channel codes based on i.i.d. noise models are not always efficient in correcting video prediction errors. In addition, some of the prediction errors do not cause perceptible visual distortions. From perceptual coding point of view, there is no need to correct such errors. This paper proposes a scheme for the decoder to perform perceptual quality analysis on the predicted side information. The decoder only requests parity bits to correct visually sensitive errors. More importantly, with the proposed technique, key frames can be encoded at higher rates while still maintaining consistent visual quality across the video sequence. As a result, even the objective PSNR measure of the decoded video sequence will increase too. Experimental results show that the proposed technique improves the R-D performance of a transform domain DVC codec both subjectively and objectively. Comparisons with a well-known DVC codec show that the proposed perceptual-based DVC coding scheme is very promising for distributed video coding framework.     

Side information generation with auto regressive model for low-delay distributed video coding

In this paper, we propose an auto regressive (AR) model to generate the high quality side information (SI) for Wyner-Ziv (WZ) frames in low-delay distributed video coding, where the future frames are not used for generating SI. In the proposed AR model, the SI of each pixel within the current WZ frame t is generated as a linear weighted summation of the pixels within a window in the previous reconstructed WZ/Key frame t − 1 along the motion trajectory. To obtain accurate SI, the AR model is used in both temporal directions in the reconstructed WZ/Key frames t − 1 and t − 2, and then the regression results are fused with traditional extrapolation result based on a probability model. In each temporal direction, a weighting coefficient set is computed by the least mean square method for each block in the current WZ frame t. In particular, due to the unavailability of future frames in low-delay distributed video coding, a centrosymmetric rearrangement is proposed for pixel generation in the backward direction. Various experimental results demonstrate that the proposed model is able to achieve a higher performance compared to the existing SI generation methods.     

Low complexity distributed video coding

ContextConventional video encoding is a computationally intensive process that requires a lot of computing resources, power and memory. Such codecs cannot be deployed in remote sensors that are constrained in terms of power, memory and computational capabilities. For such applications, distributed video coding might hold the answer.ObjectiveIn this paper, we propose a distributed video coding (DVC) architecture that adheres to the principles of DVC by shifting the computational complexity from the encoder to the decoder and caters to low-motion scenarios like video conferencing and surveillance of hallways and buildings.MethodThe architecture presented is block-based and introduces a simple yet effective classification scheme that aims at maximizing the use of skip blocks to exploit temporal correlation between consecutive frames. In addition to the skip blocks, a dynamic GOP size control algorithm is proposed that instantaneously alters the GOP size in response to the video statistics without causing any latency and without the need to buffer additional frames at the encoder. To facilitate real-time video delivery and consumption, iterative channel codes like low density parity check codes and turbo codes are not used and in their place a Bose–Chaudhuri–Hocquenghem (BCH) code with encoder rate control is used.ResultsIn spite of reducing the complexity and eliminating the feedback channel, the proposed architecture can match and even surpass the performance of current DVC systems making it a viable solution as a codec for low-motion scenarios.ConclusionWe conclude that the proposed architecture is a suitable solution for applications that require real-time, low bit rate video transmission but have constrained resources and cannot support the complex conventional video encoding solutions.Practical implicationsThe practical implications of the proposed DVC architecture include deployment in remote video sensors like hallway and building surveillance, video conferencing, video sensors that are deployed in remote regions (wildlife surveillance applications), and capsule endoscopy.     

Side information refinement using motion estimation in dc domain for transform-based distributed video coding

The key to good decoding performance in distributed video coding systems lies in the efficient prediction of frames using side information. Previously, this process has been performed without considering the progressive nature of the synthesis of the final frame. Observing the fact that incorrectly predicted areas of the current frame can be detected at different levels of final frame synthesis, an algorithm is proposed for refinement of side information synthesis based on an additional stage of motion estimation. The additional stage is performed on correctly decoded DC frames and is used to significantly improve the motion prediction of the final resolution frames, which leads to enhanced performance of the overall system.     

Iterative wyner-ziv decoding for unidirectional distributed video coding

Unidirectional distributed video coding (DVC) is one of the untouched areas of DVC, which has to be necessarily employed when the feedback channel is not available. Thus, to serve that purpose, proposed is a unidirectional distributed video coding using a parallel Wyner-Ziv architecture. Simulation results show that up to 6.5 dB PSNR gain can be obtained with the proposed codec over the conventional DVC codec with no feedback channel at the same bit rate and the computational cost     

Nonlinear quantisation for pixel domain distributed video coding

A nonlinear quantisation algorithm for pixel domain distributed video codec (DVC) is proposed. A residual signal is generated at the encoder considering the Wyner-Ziv frame to be encoded and adjacent reference frames and this residual signal is quantised using a nonlinear quantiser. The proposed algorithm is simulated for a number of test video sequences and the results depict a significant improvement of rate distortion performance, by reducing the bit rate while keeping the same PSNR when compared with available pixel domain DVC codec that uses a linear quantiser.     

无反馈分布式视频编码中的速率控制算法

针对现有比特平面级编码端速率控制算法估计精度要求高的问题,提出了一种帧级编码端速率控制算法。该算法通过在编码端利用分层快速运动补偿内插产生高质量的边信息估计,并根据循环移位去除比特平面间的级别性,使每个比特平面的编码速率均匀化,从而实现帧级别的速率控制。实验结果表明,与现有算法相比,所提算法对中高速运动视频边信息估计质量有明显提升,且解码视频的平均PSNR(peak signal-to-noise ratio)均有提高。     

Sequential motion estimation using luminance and chrominance information for distributed video coding of Wyner-Ziv frames

Proposed is a novel side information refinement technique for Wyner-Ziv video frames in distributed video coding using sequential motion compensation with luminance and chrominance information for a given bit plane to update the side information for the next bit plane. Simulation results show that over 3 dB PSNR gain can be obtained with the proposed algorithm over the best available pixel domain Wyner Ziv codec from the literature [Natario et al.] at the same bit rate.     

Rate-distortion driven decoder-side bitplane mode decision for distributed video coding

Distributed video coding (DVC) features simple encoders but complex decoders, which lies in contrast to conventional video compression solutions such as H.264/AVC. This shift in complexity is realized by performing motion estimation at the decoder side instead of at the encoder, which brings a number of problems that need to be dealt with. One of these problems is that, while employing different coding modes yields significant coding gains in classical video compression systems, it is still difficult to fully exploit this in DVC without increasing the complexity at the encoder side. Therefore, in this paper, instead of using an encoder-side approach, techniques for decoder-side mode decision are proposed. A rate-distortion model is derived that takes into account the position of the side information in the quantization bin. This model is then used to perform mode decision at the coefficient level and bitplane level. Average rate gains of 13–28% over the state-of-the-art DISCOVER codec are reported, for a GOP of size four, for several test sequences.     

Turbo trellis coded modulation for transform domain distributed video coding

A transform domain distributed video coding (DVC) codec is proposed using turbo trellis coded modulation (TTCM). TTCM symbols are generated at the DVC decoder using the side information and the parity bits received from the DVC encoder. These generated symbols are used at the TTCM-based DVC decoder to decode the bit stream. Simulation results show that a significant rate-distortion performance gain can be achieved using the proposed codec compared to the best state-of-the-art transform domain DVC codecs discussed in the literature.     

Rate estimate for regular LDPCA codec in distributed video coding

Accumulated low density parity check (LDPCA) codec is proposed for DISCOVER project in distributed video coding (DVC),which offers flexible coding rate.Although it can use feedback channel to adapt the...     

分布式视频编码中基于滑窗的自适应相关估计方法

信源与边信息之间的相关建模和参数估计一直是分布式视频编码的关键环节。在分布式视频编码中,相关噪声分布是非平稳的,会随着场景序列而动态变化,如何准确地预测和追踪相关参数十分重要。为了充分发挥分布式信源编码的优势,提出一种基于滑窗的自适应相关估计方法。该方法将滑窗的思想嵌入到基于LDPCA码的Slepian-Wolf解码器中,结合边信息和码流在线估计图像信源之间的相关参数,且能够自适应地选择是否进行重估,进而优化联合比特面置信传播迭代译码。实验结果表明,以先进的分布式视频编码方案DISCOVER作为基准,使用所提方法的方案在保持较低编码复杂度的情况下提高系统的率失真性能。     

无反馈分布式视频编码中Wyner-Ziv帧的顽健重构算法

在无反馈分布式视频编码系统中,提出了一种Wyner-Ziv帧的顽健重构算法。针对比特面解码错误带来的视频质量下降问题,对DC系数和AC系数使用不同重构方法,特别是对于解码失败的DC系数量化值,利用编码端原始图像的相关信息自适应地调整边信息量化值和解码失败量化值对重构的贡献,从而完成重构。实验结果表明,与最小均方误差重构算法相比,该算法可以有效提高解码视频的平均PSNR(peak signal-to-noise ratio),且解码视频图像的主观质量有明显改善。     

分布式视频编码中基于量化噪声因素的虚拟相关信道模型

针对现有虚拟信道模型——Laplacian模型不能精确描述其特性,导致系统编码率失真性能不高,深入研究了量化噪声对边信息质量的影响,引入量化噪声因素修正虚拟信道模型,改进了像素域分布式视频编码(PDWZ)系统的帧级虚拟信道估计,并利用原始图像相关信息实现参数的动态调整。实验结果表明,与现有Laplacian模型相比,改进模型能更精确地描述虚拟信道的统计特性,系统的率失真性能得到改善。     

Performance evaluation of wavelet-based distributed video coding schemes

In this paper we propose and compare different distributed video coding (DVC) schemes based on the use of the wavelet transform, which naturally allows for spatial and other forms of scalability. In particular, we propose a hybrid encoder which utilizes channel codes, and evaluate its performance in the absence of a feedback channel. The proposed scheme uses statistical models for the estimation of the required bitrate at the encoder. We also propose a scheme that is based on a modulo reduction procedure and does not use channel codes at the receiver/transmitter. These schemes are compared with more conventional coders that do not or only partially exploit the distributed coding paradigm. Experimental results show that the considered schemes have good performance when compared with similar asymmetric video compression schemes, and that DVC can be an interesting option in appropriate scenarios.     

Content-based group-of-picture size control in distributed video coding

Controlling the group of picture (GOP) size in distributed video coding (DVC) is a difficult but important task since it has a direct impact on the coding performance. This paper presents a framework to adaptively control the size of GOPs in a Wyner–Ziv encoder by means of encoder-side decisions based on support vector machines (SVM) that uses simple features extracted from the original video content. To train the SVM, firstly this work proposes how to compute the sequence of GOP sizes with the best rate-distortion performance given the set of GOP sizes that can be used during the encoding process. Then, an algorithm based on the previously trained SVMs is presented to control the actual GOP size each time a new decision can be taken at the encoder. Results show that the proposed algorithm can achieve a rate distortion performance close to the ideal one. Moreover, comparisons with a reference adaptive GOP size selection algorithm in the literature shows gains up to 2 dB PSNR in the best conditions.     

Independent key frame coding using correlated pixels in distributed video coding

A novel intra-coding technique is proposed that eliminates the requirement of a secondary coding scheme for coding the key frames in distributed video coding (DVC). The proposed technique uses the Slepian-Wolf theorem and Wyner-Ziv (WZ) coding with spatially predicted information to transmit the key-frames to the DVC decoder. Simulation results show that the proposed WZ-intra coding technique (WZ-I) can achieve up to 5 dB PSNR gain compared to MPEG-2 intra coding (MPEG-I) at the same bit rate with negligible computational cost to the encoder