基于上下文的自适应二进制算术熵编码

H.264在主要档次中采纳了基于上下文的自适应二进制算术编码（CABAC）的熵编码方案。深入研究了CABAC的二进制化、上下文建模和自适应二进制算术编码器,并利用测试模型进行测试,实验结果表明：在相同测试序列下,CABAC和CAVLC相比的确能节省较大的比特率。     

一种低硬件消耗的CABAC编码器研究与实现

基于上下文的自适应算术编码(CABAC)是H.264标准中的一个重要创新.通过算术编码与自适应上下文模型的结合使其可以获得很高的压缩比,相对于CAVLC其可以获得9%～14%码率的降低.CABAC作为一种新型的熵编码方法,其将自适应技术、上下文模型化和二进制算术编码有效的结合在了一起,并采用查表的乘法与概率估计,使得CABAC在硬件实现方面比较方便.在此提出了一种适用于1080P(@30Hz)的低硬件消耗的CABAC编码器,采用SMICO.18μmCMOS工艺实现,其理想速度可以达到200MHz.该编码器可以应用于高清视频编码领域.     

H.264/AVC中的熵编码技术分析与研究

H.264/AVC是由国际电信联盟(ITU)和国际标准化组织(ISO)共同制定的新一代视频编码标准。该标准的残差数据熵编码方案采用了基于上下文的自适应可变长编码CAVLC与基于上下文的自适应二进制算术编码CABAC。阐述了两种熵编码的基本原理,并对其性能进行了相应的实验测试。结果表明:在相同的图像质量下,CABAC熵编码计算复杂度较高,但较CAVLC熵编码有较大幅度的编码增益,可节约6%-12%的码率。     

一种高效的CABAC解码器硬件结构设计

相对于其他熵编码而言,基于上下文的自适应二进制算术熵编码（CABAC）具有更大的数据压缩率,但由于其运算复杂,访问存储设备频繁,导致编／解码率较低。针对影响CABAC解码速度的“瓶颈”问题,提出了一种高效的CABAC解码器硬件结构,包括新的存储访问方式、优化的解码核心单元结构以及子解码器级联的方式。实验结果表明,该硬件结构可显著提高CABAC的解码效率。     

高清CABAC解码器的优化设计和实现

针对基于上下文的自适应二进制算术编码(CABAC)解码过程中数据依赖性强、并行度低的问题,提出一种优化的硬件结构来实现H.264/AVC高级档次高清视频序列的实时解码。该结构基于二级存储结构,采用语法元素合并和预测技术,对解码判决过程进行优化并对反二值化模块的电路进行复用。测试结果表明,该系统在较小的面积下能达到较高的性能,在FPGA上可以满足高清视频序列的实时CABAC解码需求。     

基于上下文的自适应二阶二进制算术编码算法

H．264是国际上最新的视频编解码标准，是未来几年内视频编码技术研究的主要方向。基于上下文的二进制算术编码算法（CABAC）是H．264中一种能适应信号统计特性的变化，容易达到渐进性能的高效率的熵编码算法。提出了基于CAB-AC的二阶二进制算术编码算法（2-CABAC），把待编码比特流binstring转换成theta string，通过对theta string进行编码提高对bin string的压缩比。给出了2-CABAC的原理、设计方法和程序流程。测试结果表明，与CABAC相比较，2-CABAC明显提高了压缩比。最后，对转换函数Phi的设计进行了讨论。     

基于运动矢量差（MVD）的CABAC新算法*

在H.264/AVC视频编码标准中,基于上下文的自适应二进制算术编码（CABAC）主要应用于主要档次中,并且具有较高的压缩效率。首先分析了CABAC编码原理和运动矢量差（MVD）各分量的上下文模型选择原理,而后提出了在帧间编码分割块尺寸下,充分地利用当前块MVD与当前块MV的相关性、当前块MVD与已编码相邻块MVD的相关性以及当前块MVD中各分量之间相关性的CABAC优化算法（CABAC₁算法）。通过实验表明:较基准CABAC算法,CABAC₁算法一方面能有效地降低2%左右的编码时间及确保了编码序列的视觉质量;另一方面能够有效地节约在编码中帧间编码帧的码流（比特流）,其中P帧平均节约了10%左右的比特流,B帧节约了5%左右的比特流。因此,CABAC₁算法是一种有效的优化算法。     

基于概率估计更新的CABAC加速算法

基于上下文的自适应二进制算术编码（context-based adaptive binary coding,CABAC）是一种高效的熵编码方法,但是其高计算复杂度制约了该算法的编码速度,已成为其应用的一个主要瓶颈。为解决此问题,在分析CABAC算法及其计算复杂度的基础上,对其概率估计更新部分进行了改进,提出了一种提高其编码速度的有效方法。该方法首先以N个符号的包为单位进行编码,仅每个包编码完成后再进行一次概率估计的更新,因而成倍地降低了概率估计更新的频度。实验数据表明,该方法较以往的方法使CABAC的编码速度平均提高了133%~307%,同时编码效率平均下降187%~298%。     

改进的CABAC与SPIHT编码算法研究

为提高图像压缩效率,提出了分段自适应二进制算术编码CABAC与SPIHT算法相结合的混合编码算法,并从理论和仿真实验两个方面证明了该算法的有效性。根据SPIHT算法产生码流概率的特点及二进制熵编码的特性将SPIHT算法产生的二进制码流分为符号和数据两段,并按照SPIHT编码阈值对数据码流再次分段,采用优化的CABAC对各二进制码流段分别编码,在不增加计算量的情况下能够得到更好的图像压缩效果。     

H.264中自适应二进制算术编码器的FPGA实现

H.264是目前国际上最新、最有前途的视频压缩标准,基于上下文的自适应二进制算术编码是H.264中一种高效的熵编码,但算法比较复杂,执行速度不高。本文提出一种基于流水线的自适应二进制算术编码器的FPGA结构。在实现过程中,对原有的软件流程进行了部分改进以满足硬件实现要求,采用流水线及并行处理技术设计整个电路。     

High throughput entropy decoder design for H.265/HEVC

Multimedia Tools and Applications - The H.265/high efficiency video coding (HEVC) standard employs context-based adaptive binary arithmetic coding (CABAC) as a single entropy coding method. Despite...     

并行可配置的HEVC熵编码的VLSI结构

提出了一种并行的可配置HEVC熵编码的VLSI结构。通过对HEVC参考软件算法分析,针对HEVC中CABAC编码采用高度并行的语法元素处理方式,设计了针对CABAC中语法元素并行处理的硬件结构。同时采用可配置的PE-Array结构,在提高了吞吐率和计算效率的同时,平衡了VLSI设计中面积过大的问题。在SMIC 0.13μm工艺库下,进行了逻辑综合,系统总门数为16.2 K,片上存储为20.8 KB。在时钟频率300 MHz下,可处理3 840×2 160@30 frame/s的视频序列。     

基于CABAC和去耦合码率估计技术的H.264/AVC帧内模式选择方法研究

本文提出了一种简单有效的帧内模式选择方法,通过分析CABAC熵编码中色度分量与量度分量的交织信息,去除耦合,同时在率失真优化过程中部分引入部分码率估计方法,降低模式选择的计算复杂度,提高模式选择速度。大量的实验结果表明,本文提出的方法对全I帧序列能够带来66.4%的时间节省,同时几乎不损失编码图像质量;对IBBP序列能够达到平均10%的时间节省,同时部分序列甚至比JM有更好的R-D曲线。     

A Very Low Bit Rate Video Coding Combined with Fast Adaptive Block Size Motion Estimation and Nonuniform Scalar Quantization Multiwavelet Transform

We describe a very low bit rate video coding framework in which motion correlation between successive video frames is exploited in the multiwavelet transform domain. Some complicated techniques, such as spatial prediction in intra coding, adaptive block size motion estimation, more than one previous frames for prediction in inter frames, and content adaptive binary arithmetic coding (CABAC) are used in H.26L standard. The testing results show that H.26L can greatly outperform MPEG-4 ASP in both PSNR and visual quality. However, the encoding of H.26L costs too much time for it is complex to use fast motion search in adaptive block size motion estimation, and CABAC needs much time to generate the code list for entropy coding. Whereas, only four types of symbol are generated after zero tree wavelet coding so that the entropy coding can cost less time than CABAC. Moreover, if we select 8× 8 sized block as a basic mode, which can be united into the large size mode if neighbored 8× 8 sized blocks have same reference frame and motion vector, then the fast motion estimation can be feasible. Accordingly, a fast motion search algorithm, multiwavelet transform, and a novel adaptive quantization schemer are applied to the proposed coding frame. Experimental results reveal 0.2–0.5 dB increase in coded PSNR at low bit rates over the state-of-the-art H.26L recommendation, and similar improvements over MPEG-4 at high bit rates, with a considerable improvement in subjective reconstruction quality, while simultaneously supporting a scalable representation.Jiazhong Chen was born in 1970. He received the M.S. degree in computation mathematics in 1999 and Ph.D. degree in computer system architecture in 2003 from HUST. He is now a lecturer at School of Computer science and technology of HUST. His main research interests include signal processing and wavelet analysis, image and video coding.Jingli Zhou was born in 1946. She received the B.E. degree in 1969. She is a Professor and doctor advisor at university of science and technology. She had been a visiting scholar in USA from 1995 to 1996 and has been honor of the State Department Special Allowance since 1999. Her main field of research: computer network and multimedia signal processing.Shengsheng Yu was born in 1944. Received the B.E. degree in 1967. He is a Professor and doctor advisor at university of science and technology. He had been a visiting scholar in west Germany from 1982 to 1983. His main field of research: computer network and storage, discrete signal processing and communication.Jun Xu was born in 1981. He received the B.S. degree from HUST, Wuhan, P. R. China, in 2003. He is now pursuing his M.S. degree in the School of Computer Science and Technology of HUST. His research interests are wavelet analysis, image compression and video processing and communications.     

H.26L视频编码算法性能分析

H.2 6 L 是新一代的视频编码标准 .同现有的视频编码标准相比 ,新标准具有更高的编码效率和图象质量 ,在容错能力和网络适应性方面也有新的特点 .采用 Bjntegaard提出的性能评估方法比较了 H.2 6 L 和 H.2 6 3的编码性能差异 ;在此基础上 ,用标准图象序列对 H.2 6 L 独有的几种编码技术进行了仿真 ,定量分析了它们对提高编码性能的贡献 ,这对算法的进一步改进和优化具有很高的参考价值 .     

High-efficiency pipeline design of binary arithmetic encoder

This paper focuses on the pipeline design of context-based adaptive binary arithmetic coding(CABAC).CABAC is a well-known bottleneck in very large scale integration circuit design of H.264/AVC encoder.Despite its high performance,the tight feedback loops of CABAC make parallelization difficult.Most researchers are concerned about multi-bin processing regardless of pipeline design.However,without pipeline,the overall performance becomes significantly limited.In this paper,the critical path for the hardware implementation of binary arithmetic encoder(BAE)was analyzed in detail.We break down the computing steps to the best extent,and rearrange such steps to the appropriate pipeline to achieve a balanced latency at each stage.Moreover,a new BAE architecture with a five-stage pipeline and one bin per cycle is proposed,the latency of critical path is substantially reduced,and the frequency and throughput rate are improved.An field-programmable gate array implementation of the proposed pipelined architecture in our H.264 encoder is capable of a 190 Mbps encoding rate.A maximum 483 MHz could be achieved on SMIC 0.13μm technology,which meets the requirements of quad full high-definition encoding at 30fps.The proposed architecture can be utilized in other designs to achieve improved performance.