Wyner-Ziv视频编码中无反馈速率控制算法研究

为了避免在分布式视频编码系统中使用反馈信道,提出了一种基于Wyner-Ziv编码的无反馈速率控制算法。首先,利用目标码率和目标帧率进行GOP层码率分配;然后,根据原始图像的帧间相关性动态选择量化因子和量化矩阵来分配每个GOP内关键帧和Wyner-Ziv帧的比特数;接下来,利用系数带级的相关性计算相关噪声模型参数,并选择对应的LDPC校验矩阵,提出Wyner-Ziv帧的无反馈比特面速率控制算法。实验结果表明,在给定目标码率下,所提算法的编码码率误差小于0.57%,且与现有无反馈速率控制算法相比,解码恢复图像的PSNR(峰值信噪比)可以提高1dB。另外,该算法基本没有增加编码端复杂度,可用于实际分布式视频通信系统。     

Region-of-interest based rate control for UAV video coding

To meet the requirement of high-quality transmission of videos captured by unmanned aerial vehicles (UAV) with low bandwidth, a novel rate control (RC) scheme based on region-of-interest (ROI) is proposed. First, the ROI information is sent to the encoder with the latest high efficient video coding (HEVC) standard to generate an ROI map. Then, by using the ROI map, bit allocation methods are developed at frame level and large coding unit (LCU) level, to avoid inaccurate bit allocation produced by camera movement. At last, by using a better robustness R-λ model, the quantization parameter (QP) for each LCU is calculated. The experimental results show that the proposed RC method can get a lower bitrate error and a higher quality for reconstructed video by choosing appropriate pixel weight on the HEVC platform.     

Adaptive rate control algorithm for low power video coding systems

With the recent development of third-generation communication technologies, low power video coding system (such as PDA, Handphone or system on chip) has found wide applications such as live video using a PDA and sharing it among friends, etc. However, video coding in a low power system has two major hurdles to overcome: (1) In a low power system, video coding needs to meet the rigorous constraints of the available memory and computational capacity; (2) In a low power system, the computational power allocated to video coding may vary drastically (in bursts). In this paper, a new adaptive rate control algorithm is proposed for low power video coding system. This adaptive rate control scheme takes into account the time constraint of a low power system, and its bit allocation depends not only on the available data bits, but more importantly, on the available coding time. Experimental results show that, compared to the existing rate control scheme, the new algorithm can always achieve the maximum frame rate, maximize the utilization of the available bandwidth and computing power, increase the average PSNR, and improve the subjective perceptual quality of the reconstructed video.     

A low-complexity rate allocation algorithm for joint source-channel video coding

The problem of enabling robust video transmission over lossy networks has become increasingly important because of the growing interest in video delivery over unreliable channels such as wireless networks. The more the coding process relies on an intensive use of prediction to improve the coding gain, the more the reconstructed sequence proves to be sensitive to information losses. As a matter of fact, it is necessary to introduce some redundant data in order to increase the robustness of the coded bit stream. A possible solution can be found filling a matrix structure with RTP packets and applying a Forward Error Correction (FEC) code on its rows. However, the matrix size and the chosen FEC code affect the performance of the coding system. The paper proposes a novel adaptation technique that tunes the amount of redundant information included in the packet stream and differs from previously proposed solutions since it relies on the percentage of null quantized transform coefficients in place of the activity or the Mean Square Error (MSE). This strategy is then integrated in a joint source-channel coder rate allocation algorithm that shares the available bits between the H.264/AVC coder and the channel coder according to the significance of the frame in the decoding process. Experimental results show that the presented approach significantly improves the quality of the reconstructed sequences at the decoder with respect to activity-based strategies and requires a low computational complexity.     

A self-governing rate buffer control strategy for pseudoconstantbit rate video coding

Video coding is a key to successful visual communications. An interframe video coding algorithm using hybrid motion-compensated prediction and interpolation is considered for coding studio quality video at a bit rate of over 5 Mb/s. Interframe coding without a buffer control strategy usually results in variable bit rates. Although packet networks may be capable of handling variable bit rates, in some applications, a constant bit rate is more desirable either for a simpler network configuration or for channels with fixed bandwidth. A self-governing rate buffer control strategy that can automatically steer the coder to a pseudoconstant bit rate is considered. This self-governing rate buffer control strategy employs more progressive quantization parameters, and constrains quantizer adjustments so that a smoother quality transition can be attained. Simulation results illustrate the performance of the pseudoconstant bit rate coder with this buffer control strategy.     

A two-pass rate control algorithm for H.264/AVC high definition video coding

In this paper, we propose a novel two-pass rate control algorithm to achieve constant quality for H.264/AVC high definition video coding. With the first-pass collected rate and distortion information and the built model of scene complexity, the encoder can determine the expected distortion which could be achieved in the second-pass encoding under the target bit rate. According to the built linear distortion-quantizer (D-Q) model, before encoding one frame, the quantization parameter can be solved to realize constant quality encoding. After encoding one frame, the model parameters will be updated with linear regression method to ensure the prediction accuracy of the quantization parameter of next encoded frame with the same coding type. In order to obtain the expected distortion of each frame under the target bit rate, a GOP-level bit allocation scheme is also designed to adjust the target bit rate of each GOP based on the scene complexity of the GOP in the second-pass encoding. In addition, the effect of scene change on the updating of D-Q model is considered. The model will be re-initialized at the scene change to minimize modeling error. The experimental results show that compared with the latest two-pass rate control algorithm, our proposed algorithm can significantly improve the bit control accuracy at comparable coding performance in terms of constant quality and average PSNR. On average, the improvement of bit control accuracy achieved about 90%.     

Recent advances in rate control for video coding

In this paper, we review the recent advances in rate control techniques for video coding. The rate control algorithms recommended in the video coding standards are briefly described and analyzed. Recent advances, such as new concepts in rate-distortion modelling and quality constrained control, are presented. With these techniques, the rate control performance can be improved. The paper not only summarizes these recent rate control techniques but also provides explicit directions for future rate control algorithm design.     

Leaky-bucket based rate control algorithm for C VBR video encoding

A rate control algorithm is presented for constrained variable bit rate (C VBR) encoding to make the compressed video stream more friendly to the user network interface (UNI) than in free VBR coding. Experiments show that the algorithm would not only meet the delay constraint and traffic contract of VBR transfer so as to avoid the cell loss over UNI, but also benefit the statistical multiplexing by reducing the burstiness of the MPEG encoded stream     

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。     

Gamma rate theory for causal rate control in source coding and video coding

The rate distortion function in information theory provides performance bounds for lossy source coding. However, it is not clear how to causally encode a Gaussian sequence under rate constraints while achieving R–D optimality. This problem has significant implications in the design of rate control for video communication. To address this problem, we take distortion fluctuation into account and develop a new theory, called gamma rate theory, to quantify the trade-off between rate and distortion fluctuation. The gamma rate theory implies that, to evaluate the performance of causal rate controls in source coding, the traditional R–D metric needs to be replaced by a new GRD metric. The gamma rate theory identifies the trade-off between quality fluctuation and bandwidth, which is not known previously. To validate the gamma rate theory, we design a rate control algorithm for video coding; our experimental results demonstrate the utility of the gamma rate theory in video coding.     

Novel video coding algorithm based on 3D-binDCT

In this paper we propose a three dimensional multiplierless discrete cosine transform（DOT） with lifting scheme called 3D-binDCT. Based on 3D-binDCT, a novel video coding algorithm without motion estimation/compensation is proposed. It uses the 3D-binDCT to exploit spatial or temporal redundancy. The computation of binDOT only needs shift and addition operations, thus the computational complexity is minimized. DO coefficient prediction, modified scan mode and arithmetic coding techniques are also adopted. Extensive simulation results show that the proposed coding scheme provides higher coding efficiency and improves visual aualitv, and it is easy to be realized by software and hardware.     

一种基于JVT的比特率控制方法

比特率在视频编码中具有重要作用。正在制定的JVT视频编码标准并没有提供比特率控制方法,为此本文提出了一种基于JVT的比特率控制方法。在其图像层比特率控制中,引入PID控制器来提高比特率控制的鲁棒性;在宏块层通过宏块16×16模式运动估计得到的SAD来计算宏块的活动性,降低了算法复杂度。实验结果表明,该方法在保证不影响JVT原有编码效率的前提下,获得了较高的控制精度,同时也具有较强的鲁棒性。     

基于H.264标准的码率控制改进算法

本文利用视频编码的线性码率控制(RC)算法(Rho-Domain算法)对原有的H.264标准中的RC算法进行了改进.首先,对于视频序列中的Ⅰ帧图像,使用Rho-domain算法进行码率控制.由于该算法基于本帧的图像内容,所以能够及时地对Ⅰ帧进行精确的码率调整;其次,使用了新的关于P帧的比特分配原则,根据GOP中的位置来分配P帧的比特数;最后,对模型的估算方法作了改进,使模型参数的计算更为精确.实验结果表明,改进后的算法能更加有效准确的控制编码序列的码率.     

Evolution strategy based rate controlling for off-line video coding

An intelligent rate control technique for H.264/AVC using the subjective quality of video is proposed. A subjective video quality metric is used with an evolution strategy algorithm, which is capable of identifying the best possible quantisation parameters for each frame/macroblock to encode the video sequence such that it would maximise the subjective quality of the entire video sequence subjected to the target bit rate. Simulation results show that up to 40% bit rate saving can be achieved with the proposed technique at the same video quality.     

改进的3D DCT视频编码方案

文中详细研究了离散余弦变换（DCT）的原理及统计特性,提出一种改进的3D DCT的视频编码方案。该算法在不影响信噪比的情况下,运算量减少了1/7,且编码与解码的运算量相当。     

视频编码预处理算法研究

针对现有降噪采用时空域滤波、去块效应采用环路滤波/后处理这种分而治之方案的缺点,通过分析降噪的基本技术、低码率视频应用中块效应产生的原因和去块效应的常用方法,从滤除不需要或相对不重要的高频离散余弦变换(DCT,discrete cosine transform)系数角度提出了降噪和去块效应可同时处理的设想。新提出的预处理算法是根据图像纹理特性、运动情况和码率约束等,在图像的不同区域采用不同强度的自适应双边滤波,这样不仅去噪,滤除不重要的细节以便于高效压缩,避免块效应的产生,同时也可起到一定程度的码率控制效果。     

一种新的低功耗图像及视频编解码算法

提出一种新的低功耗图像及视频编解码算法。该算法主要基于矢量量化,认为编码算法的质量和功耗地码本尺寸的大小,通过采用小尺寸码本,降低算法所需要的内存数量,从而降低功耗。编码时,利用分形理论中的同构变换计算虚拟码本,弥补由于采用小码本造成的图像质量损失,并使编码过程较少依赖于码本内存。编解码结果与全搜索型矢量量化算法相比,在不损失图像质量的前提下,可以极大地降低编解码功耗。     

基于图像复杂度及运动信息的码率控制算法

JVT-H017是H.264视频编码标准中采用的码率控制算法提案,但在许多实时场景应用中该算法还存在平均绝对差值(MAD)预测不准确等一些不足.针对现有码率控制技术的缺陷,提出一种改进的基本单元层码率控制算法.一方面在基于图像复杂度和运动信息的基础上采用了4种时空加权模型预测平均绝对差值,并且采用运动矢量信息对图像复杂程度进行判定;另一方面结合MAD的变化情况分配目标比特.实验结果表明,相比于JVT-H017和一些新的文献算法,改进算法的编码图像峰值信噪比得到了提高,同时实际码率更接近于目标码率,码率控制性能更优越.     

Color correction algorithm based on camera characteristics for multi-view video coding

Various types of multi-view camera systems have been proposed for capturing three dimensional scenes. Yet, color distributions among multi-view images remain inconsistent in most cases, degrading multi-view video coding performance. In this paper, we propose a color correction algorithm based on the camera characteristics to effectively solve such a problem. Initially, we model camera characteristics and estimate their coefficients by means of correspondences between views. To consider occlusion in multi-view images, correspondences are extracted via feature-based matching. During coefficient estimation with nonlinear regression, we remove outliers in the extracted correspondences. Consecutively, we generate lookup tables for each camera using the model and estimated coefficients. Such tables are employed for fast color converting in the final color correction process. The experimental results show that our algorithm enhances coding efficiency with gains of up to 0.9 and 0.8 dB for luminance and chrominance components, respectively. Further, the method also improves subjective viewing quality and reduces color distance between views.