新一代视频编码标准HEVC变换方法的研究

高性能视频编码( HEVC)将成为国际最新的视频编解码标准.该标准主要针对目前应用日益广泛的高清甚至超高清视频而开发,其编码的性能目标是在保持原来H.264/AVC的视频质量的同时,将比特率再降低一半.与原有标准一样,HEVC对帧内或帧间的残差信号进行正交变换以集中能量至矩阵左上角,然而H.264/AVC标准中的传统DCT方法对于高清视频的处理已不能有较好效果.讨论研究目前针对HEVC正交变换提出的变换方法,包括基于模式的方向变换MDDT、自适应离散余弦/正弦变换(DCT/DST)、旋转变换(ROT)、IDCT修剪和变换跳过模式(TSM)等方法.实验结果显示了上述几种方法在比特率降低、编码时间缩短、软硬件实现复杂度降低和客观视频质量等方面的改进.最后,提出了对HEVC正交变换的进一步研究方向.     

基于H.264/AVC视频的低频隐写算法

在分析现有视频信息隐藏算法的基础上,结合H.264/AVC视频低频域系数的特征,提出一种基于H.264/AVC低频域视频信息隐藏算法。在量化后的离散余弦变换(DCT, discrete cosine transform)块低频区中,选取3个绝对值最大的非零系数,用改进的矩阵编码的方法嵌入信息。实验结果表明,该算法能够实现实时嵌入和提取信息,信息嵌入容量大,嵌入效率高,对视频质量影响较小等特点。     

H.264中DCT/IDCT/Hadamard变换多时钟方式的FPGA实现

DCT/IDCT/Hadamard变换被广泛应用于多种视频编码标准中,而H.264/MPEG-4AVC作为新一代的视频压缩标准,它具有在相同图像质量下比其他视频压缩标准拥有更高的压缩率的特性[1],因此对于H.264/MPEG-4AVC中的DCT/IDCT/Hadamard变换的研究就有着十分重要的意义。对于H.264/MPEG-4AVC中变换算法进行分析,并且提出一种可用的高效的硬件实现电路结构,此电路结构能够并行计算4输入像素数据。     

消除帧内误差传播的HEVC可逆水印算法

针对帧内实施可逆水印造成误差传播的问题,基于高效视频编码（High Efficiency Video Coding, HEVC）标准,提出一种用于消除帧内误差传播的可逆水印算法。算法充分考虑了HEVC新的编码特性,对帧内嵌入水印后的误差传播情况进行了分析,随后给出了在帧内4×4预测单元中嵌入水印后不会引起误差传播的条件;最后选出满足条件的4×4系数块,采用“和不变”方法将水印自适应地嵌入其量化离散正弦变换系数中。出于减小码率增长的考虑,全0系数块不嵌入水印。实验结果表明,该算法能够有效地消除帧内由嵌入水印引起的误差传播,从而减小视觉失真。同时,算法对码率的影响也较小。      

Motion-compensated DCT temporal filters for efficient spatio-temporal scalable video coding

Although most of the proposals for implementing motion-compensated temporal filtering (MCTF) schemes are based on the wavelet transform, in this paper, we propose an MCTF framework based on the discrete cosine transform (DCT). Using DCT decimation and interpolation, several temporal decomposition structures named motion-compensated DCT temporal filters (MCDCT-TF) are introduced. These structures are able to employ filters of any length with particular emphasis on 5/3 DCT and 7/4 DCT. The proposed MCDCT-TF and the two-dimensional (2D) DCT decimation technique are incorporated into H.264/AVC to provide spatio-temporal scalability. Compared with the current MCTF-based lifting schemes such as Haar, and 5/3 wavelet filters, simulation results show that the proposed MCDCT-TF utilizing longer tap DCT filters achieves a significant improvement in coding gain. The impact of odd/even group of frames, the decimation/interpolation ratios, and motion-compensated connectivity on the MCDCT-TF performance are also analyzed. Moreover, simulation results show that the performance of the presented scalable video coding is close to the single layer H.264/AVC and is slightly inferior to the temporal scalability supported in JSVM, the state-of-the-art scalable video coding standard, that gets its gain from Hierarchical B-pictures. However, our spatio-temporal coding scheme outperforms the spatio-temporal supported in JSVM even if it uses hierarchical B-pictures to improve its gain.     

Introduction to the High-Efficiency Video Coding Standard

The high-efficiency video coding(HEVC) standard is the newest video coding standard currently under joint development by ITU-T Video Coding Experts Group(VCEG) and ISO/IEC Moving Picture Experts Group(MPEG).HEVC is the next-generation video coding standard after H.264/AVC.The goals of the HEVC standardization effort are to double the video coding efficiency of existing H.264/AVC while supporting all the recognized potential applications,such as,video telephony,storage,broadcast,streaming,especially for large picture size video(4k × 2k).The HEVC standard will be completed as an ISO/IEC and ITU-T standard in January 2013.In February 2012,the HEVC standardization process reached its committee draft(CD) stage.The ever-improving HEVC standard has demonstrated a significant gain in coding efficiency in rate-distortion efficiency relative to the existing H.264/AVC.This paper provides an overview of the technical features of HEVC close to HEVC CD stage,covering high-level structure,coding units,prediction units,transform units,spatial signal transformation and PCM representation,intra-picture prediction,inter-picture prediction,entropy coding and in-loop filtering.The HEVC coding efficiency performances comparing with H.264/AVC are also provided.     

Quadtree-based non-local Kuan’s filtering in video compression

Transform coding has been widely used in video coding standards, such as H.264 advanced video coding (H.264/AVC) and high efficiency video coding (HEVC). But the coded video sequences suffer from annoying coding artifacts, such as blocking and ringing artifacts. In this paper, we propose the quadtree-based non-local Kuan’s (QNLK) filter to suppress the quantization noise optimally and improve the objective and subjective quality of the reconstructed frame simultaneously. The proposed filter takes advantage of the non-local Kuan’s (NLK) filter to restore the quantized signal in transform domain. Restored coefficients are then projected onto designed quantization constraint sets (QCS). Quadtree-based signaling strategy is used at the end of QNLK for adaptive filtering on/off control. Experimental results of QNLK show that the proposed method achieves significant objective coding gain and visual quality improvement, compared with both H.264/AVC high profile and HEVC.     

HEVC整数DCT变换与量化的FPGA实现

HEVC编码框架采用了比H.264/AVC面积更大的DCT变换和更为灵活的自适应量化,在提高数据处理速度的同时,降低了编解码的失真率.基于HEVC的变换量化原理和模块化的思想,采用并行流水线结构和无乘法器方案实现了整数DCT变换及量化部分.系统采用MODELSIM进行功能仿真,基于Altera公司的Cyclone Ⅱ系列可编程逻辑器件进行硬件验证测试,其最大时钟频率在170 MHz以上,数据处理能力在2 824 Mpixel/s以上,满足HEVC编码标准的性能要求,为HEVC编解码标准的硬件实现提供了参考.     

Jointly optimized spatial prediction and block transform for video and image coding

This paper proposes a novel approach to jointly optimize spatial prediction and the choice of the subsequent transform in video and image compression. Under the assumption of a separable first-order Gauss-Markov model for the image signal, it is shown that the optimal Karhunen-Loeve Transform, given available partial boundary information, is well approximated by a close relative of the discrete sine transform (DST), with basis vectors that tend to vanish at the known boundary and maximize energy at the unknown boundary. The overall intraframe coding scheme thus switches between this variant of the DST named asymmetric DST (ADST), and traditional discrete cosine transform (DCT), depending on prediction direction and boundary information. The ADST is first compared with DCT in terms of coding gain under ideal model conditions and is demonstrated to provide significantly improved compression efficiency. The proposed adaptive prediction and transform scheme is then implemented within the H.264/AVC intra-mode framework and is experimentally shown to significantly outperform the standard intra coding mode. As an added benefit, it achieves substantial reduction in blocking artifacts due to the fact that the transform now adapts to the statistics of block edges. An integer version of this ADST is also proposed.     

General Architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC Intra Frame Transcoding

The latest international video-coding standard H.264/AVC significantly achieves better coding performance compared to prior video coding standards such as MPEG-2 and H.263, which have been widely used in today’s digital video applications. To provide the interoperability between different coding standards, this paper proposes an efficient architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC intra frame transcoding, using the original information such as discrete cosine transform (DCT) coefficients and coded mode type. Low-frequency components of DCT coefficients and a novel rate distortion cost function are used to select a set of candidate modes for rate distortion optimization (RDO) decision. For H.263 and H.264/AVC, a mode refinement scheme is utilized to eliminate unlikely modes before RDO mode decision, based on coded mode information. The experimental results, conducted on JM12.2 with fast C8MB mode decision, reveal that average 58%, 59% and 60% of computation (re-encoding) time can be saved for MPEG-2, H.263, H.264/AVC to H.264/AVC intra frame transcodings respectively, while preserving good coding performance when compared with complex cascaded pixel domain transcoding (CCPDT); or average 88% (a speed up factor of 8) when compared with CCPDT without considering fast C8MB. The proposed algorithm for H.264/AVC homogeneous transcoding is also compared to the simple cascaded pixel domain transcoding (with original mode reuse). The results of this comparison indicate that the proposed algorithm significantly outperforms the mode reuse algorithm in coding performance, with only slightly higher computation.     

FITD: Fast Intra Transcoding from H.264/AVC to high efficiency video coding based on DCT coefficients and prediction modes

In the literatures, the designs of H.264 to High Efficiency Video Coding (HEVC) transcoders mostly focus on inter transcoding. In this paper, a fast intra transcoding system from H.264 to HEVC based on discrete cosine transform (DCT) coefficients and intra prediction modes, called FITD, is proposed by using the intra information retrieved from an H.264 decoder for transcoding. To design effective transcoding strategies, FITD not only refers block size of intra prediction and intra prediction modes, but also effectively uses the DCT coefficients to help a transcoder to predict the complexity of the blocks. We successfully use DCT coefficients as well as intra prediction information embedded in H.264 bitstreams to predict the coding depth map for depth limitation and early termination to simplify HEVC re-encoding process. After a HEVC encoder gets the prediction of a certain CU size from depth map, if it reaches the predicted depth, the HEVC encoder will stop the next CU branch. As a result, the numbers of CU branches and predictions in HEVC re-encoder will be substantially reduced to achieve fast and precise intra transcoding. The experimental results show that the FITD is 1.7–2.5 times faster than the original HEVC in encoding intra frames, while the bitrate is only increased to 3% or less and the PSNR degradation is also controlled within 0.1 dB. Compared to the previous H.264 to HEVC transcoding approaches, FITD clearly maintains the better trade-off between re-encoding speed and video quality.     

An improved scheme for data hiding in encrypted H.264/AVC videos

Recently, a novel scheme to hide data into encrypted H.264/AVC videos using code-word substitution has been proposed by Xu et al. However, the statistical analysis of CAVLC code-words demonstrate that Xu et al.’s work does not fully exploit redundancy existing in CAVLC code-word for data embedding. In this paper, an improved version of Xu et al.’s data hiding method in encrypted H.264/AVC videos is proposed. Specifically, when suffixLength is equal to 1, data embedding is performed by paired code-word substitution. When suffixLength is greater than 2, not the single code-word substitution but the multiple-based notational system is adopted for data embedding. Experimental results have demonstrated that the improved method is indeed capable of providing a larger embedding capacity in comparison with Xu et al.’s method. Moreover, both encryption and data embedding can be accomplished without affecting the coding efficiency of H.264/AVC by keeping exactly the same bitrate.     

Early termination strategy of HEVC based on statistical models

High efficiency video coding (HEVC) uses half of the bitrate compared to H.264/advanced video coding(AVC) for encoding the same sequence with similar quality. Because of the advanced hierarchical structures of coding units (CUs), predicting units (PUs), and transform units (TUs), HEVC can better adapt when encoding full high definition (HD) and ultra high definition (UHD) videos. At the expense of encoding efficiency, the complexity of HEVC sharply increases compared to H.264/AVC, mainly due to its quad-tree structure that splits pictures. In this study, the probability distribution, which is generated by a rate distortion optimizing (RDO) cost, is analyzed. Then, an early terminating method is proposed to decrease the complexity of the HEVC based on probability distributions. The experiment shows that the coding time is reduced by 44.9% for HEVC intra coding, at the cost of a 0.61% increase in the Bjøntegaard delta rate (BD-rate), on average.     

High performance architecture for unified forward and inverse transform of HEVC

High efficiency video coding (HEVC) transform algorithm for residual coding uses 2-dimensional (2D) 4×4 transforms with higher precision than H.264's 4×4 transforms, resulting in increased hardware complexity. In this paper, we present a shared architecture that can compute the 4×4 forward discrete cosine transform (DCT) and inverse discrete cosine transform (IDCT) of HEVC using a new mapping scheme in the video processor array structure. The architecture is implemented with only adders and shifts to an area-efficient design. The proposed architecture is synthesized using ISE14.7 and implemented using the BEE4 platform with the Virtex-6 FF1759 LX550T field programmable gate array (FPGA). The result shows that the video processor array structure achieves a maximum operation frequency of 165.2 MHz. The architecture and its implementation are presented in this paper to demonstrate its programmable and high performance.     

一种新的基于VLIW的IDCT和运动补偿算法

本文使用矩阵形式在超长指令字(VLIW)的观点下将几种经典算法与已有的适合于VLIW的算法进行了比较.然后利用VLIW结构的特性,提出了一种快速IDCT算法.与现有算法相比,新算法进一步减少了所需的指令周期.并利用VLIW结构的寄存器特性,将视频编解码过程中的运动补偿(预测)和IDCT(DCT)组合,使运动补偿所需时间降低为原来的约50%,这种思想能应用于MPEG1/2/4,H.263和H.264.     

基于纹理特征的H.264/AVC顽健视频水印算法

在分析现有视频水印算法的基础上,结合H.264压缩编码标准的特性,提出了一种新的基于纹理特征的视频顽健水印算法。算法先对当前帧4×4块进行整数离散余弦变换,判断其是否是纹理块,再采用能量差的方式自适应选择系数嵌入水印。实验结果表明,该算法对视频质量和码率的影响较小,并且能有效抵抗高斯噪声、低通滤波、重编码等常见的视频水印攻击。     

基于H.264的差错掩盖技术的研究

介绍了基本的差错掩盖技术以及最近新提出的基于H.264的差错掩盖技术,并对在编码端加入引导信息的决策树法进行了改进,给出了初步的实验结果,最后概括了这些掩盖方法的特点.     

六角变换方法在视频编码中的应用

介绍了一些有关DCT及其快速算法的关键技术,提出了六角变换方法及其应用于视频编码的近似整数实现.实验结果表明,六角变换方法不仅具有相比浮点DCT实现复杂度低、解码端无误差累积的优点,而且能提供相比其他整数近似变换更高的视频编码效率.     

An improved reversible data hiding-based approach for intra-frame error concealment in H.264/AVC

As H.264/AVC video streams are highly compressed, they become sensitive to errors caused by unreliable transmission channels. In order to address this issue, an improved version of Chung et al.’s reversible data hiding-based approach for intra-frame error concealment is proposed for H.264/AVC codec. By using the histogram shifting technique, the original work reversibly embeds the motion vector (MV) of a macroblock (MB) into other MB within the same intra-frame. If an MB is corrupted at the decoder side, the embedded MV can be extracted from the corresponding MB for the recovery of the corrupted MB. However, Chung et al.’s work did not fully exploit the number of coefficients which need to be modified in order to reversibly hiding data, and did not consider many extra nonzero residual blocks produced by data hiding. These two issues could reduce the visual quality of the stego-video. This paper adopts MV data pre-processing, the selection of most suitable embedding region, and the minimum possible amount of histogram modification, which lead to higher PSNR of the stego-video for a given payload. Experimental results further reveal that the proposed method offers stego-video with better visual quality over Chung et al.’s work.     

H.264/AVC视频编码标准的技术特点及应用分析

H.264／AVC是ITU-T视频编码专家组和ISO／IEC运动图像专家组(MPEG)共同开发出来的最新视频编码标准,它具备许多新的技术特点,如:多模式运动预测、柔性宏块排序、整数变换、一致性变字长编码、内容自适应二进制算术编码、分层编码、错误约束机制、错误掩盖技术及高效的比特流切换技术等等。本文在阐述该标准系统层结构的基础上,分析其主要技术特点及H.264／AVC VBR码流特性,阐述该标准在IP网络及无线网络中的应用情况。