Fast sample adaptive offset algorithm for 360-degree video coding

360-degree video is becoming popular with the development of the virtual reality(VR) technology in recent years. For this kind of video, pictures are projected to a two-dimensional plane. Standard video encoders are used for compression. Due to the projection mapping of the spherical video to the two-dimensional plane video, many conventional coding tools can be adjusted properly for better performance. As the 360-degree videos are high resolution videos, usually 8K resolution videos, the high complexity for encoding 360-degree videos is a problem to be solved urgently, especially for the latest video standard H.265/HEVC. Sample adaptive offset (SAO) is a new tool adopted in H.265/HEVC. It can reduce ringing artifacts and achieve higher coding efficiency. But it also introduces high computational complexity, especially on high resolution videos. In this paper, a fuzzy control based fast SAO method is proposed to reduce the high computational complexity in SAO encoding process according to the characteristics of the ERP format video. Compared with the original algorithm in the reference software HM 16.14, experimental results show that the proposed method can reduce about 73% SAO encoding time on average under the common test conditions with negligible loss.     

Data hiding in partially encrypted HEVC video

In this study, an efficient scheme for hiding data directly in partially encrypted versions of high efficiency video coding (HEVC) videos is proposed. The content owner uses stream cipher to selectively encrypt some HEVC‐CABAC bin strings in a format‐compliant manner. Then, the data hider embeds the secret message into the encrypted HEVC videos using the specific coefficient modification technique. Consequently, it can be used in third‐party computing environments (more generally, cloud computing). For security and privacy purposes, service providers cannot access the visual content of the host video. As the coefficient is only slightly modified, the quality of the decrypted video is satisfactory. The encrypted and marked bitstreams meet the requirements of format compatibility, and have the same bit rate. At the receiving end, data extraction can be performed in the encrypted domain or decrypted domain that can be adapted to different application scenarios. Several standard video sequences with different resolutions and contents have been used for experimental evaluation.     

Novel Rate Control Scheme for Low Delay Video Coding of HEVC

In this paper, a novel rate control scheme for low delay video coding of High Efficiency Video Coding (HEVC) is proposed. The proposed scheme is developed by considering a new temporal prediction structure of HEVC. In the proposed scheme, the relationship between bit rate and quantization step is exploited firstly to formulate an accurate quadratic rate‐quantization (R‐Q) model. Secondly, a method of determining the quantization parameters (QPs) for the first frames within a group of pictures is proposed. Thirdly, an accurate frame‐level bit allocation method is proposed for HEVC. Finally, based on the proposed R‐Q model and the target bit allocated for the frame, the QPs are predicted for coding tree units by using rate‐distortion (R‐D) optimization. We compare our scheme against that of three other state‐of‐the‐art rate control schemes. Experimental results show that the proposed rate control scheme can increase the Bjøntegaard delta peak signal‐to‐noise ratio by 0.65 dB and 0.09 dB on average compared with the JCTVC‐I0094 and JCTVC‐M0036 schemes, respectively, both of which have been implemented in an HEVC test model encoder; furthermore, the proposed scheme achieves a similar R‐D performance to Wang's scheme, as well as obtaining the smallest bit rate mismatch error of all the schemes.     

Frame-level bit allocation for hierarchical coding of H.265/HEVC considering dependent rate-distortion characteristics

Rate control plays an important role in video coding for rectifying the coded bit stream to meet the transmission bandwidth, which is related to two parts of bit allocation and quantization parameter acquirement. Considering that the bit allocation is a critical step due to its effect on the subsequent coding operation and rate-distortion performance, therefore in this paper an accurate H.265/HEVC frame-level bit allocation algorithm is proposed for higher coding efficiency. Concretely the feature regarding the inter-frame dependency is firstly analyzed based on the theoretical derivation. Then the hierarchically dependent characteristics are extracted and utilized to establish the bit allocation model. Experimental results show that the proposed method can guarantee a good consistency between the target bits and coded bits, where a PSNR improvement of about 0. 131 dB can be observed compared with the original H.265/HEVC bit allocation while keeping the same bit rate.     

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.     

Early Coding Unit–Splitting Termination Algorithm for High Efficiency Video Coding (HEVC)

A new‐generation video coding standard, named High Efficiency Video Coding (HEVC), has recently been developed by JCT‐VC. This new standard provides a significant improvement in picture quality, especially for high‐resolution videos. However, one the most important challenges in HEVC is time complexity. A quadtree‐based structure is created for the encoding and decoding processes and the rate‐distortion (RD) cost is calculated for all possible dimensions of coding units in the quadtree. This provides a high encoding quality, but also causes computational complexity. We focus on a reduction scheme of the computational complexity and propose a new approach that can terminate the quadtree‐based structure early, based on the RD costs of the parent and current levels. Our proposed algorithm is compared with HEVC Test Model version 10.0 software and a previously proposed algorithm. Experimental results show that our algorithm provides a significant time reduction for encoding, with only a small loss in video quality.     

基于朴素贝叶斯分类的DVC-HEVC快速转码

分布式视频编码(DVC)与传统视频编码之间的转码为移动终端设备之间的低功耗视频通信提供了一种有效的实现思路。以DVC与HEVC转码为研究对象,利用DVC解码端信息,针对高效视频编码(HEVC)中复杂度极高的编码单元(CU)划分过程进行复杂度优化研究。在DVC解码端提取与CU划分相关的纹理复杂度、运动矢量及预测残差3种特征信息;在HEVC编码端基于朴素贝叶斯原理建立CU快速划分模型,模型生成后便可以通过输入特征信息对当前CU划分进行快速决策,避免大量率失真(RD)代价计算过程。实验结果表明,本方案在编码比特率略有上升的情况下大幅缩短了HEVC编码时间,平均下降幅度达到58.26%,且几乎不影响视频质量。     

Adaptive bit allocation scheme for rate control in high efficiency video coding with initial quantization parameter determination

One of the challenges in rate control (RC) lies in how to efficiently determine a target bit rate that will be used for the quantization parameter (Q_p) calculation process during video coding. In this paper, we investigate the issues over the existing bit allocation algorithms for the RC process in High Efficiency Video Coding (HEVC) and propose an complexity-based bit allocation scheme to improve the encoding performance. First, we model the relationship between encoding bit rate and texture complexity by a linear rate function. Second, compared with traditional complexity estimation methods, a more accurate model is proposed to measure the texture complexity considering the spatial–temporal correlations. Third, based on the proposed rate function and texture complexity measurement model, we develop an adaptive bit allocation scheme for RC in HEVC. At the same time, depending on the encoder buffer status, an adaptive Q_p clip range determination algorithm is also developed to achieve the encoding quality smoothness while keeping the bit rate fluctuation at an acceptable level. Then, we exploit to determine the initial Q_p efficiently and adaptively according to video contents. Experimental results demonstrate that the proposed RC algorithm can achieve better rate-distortion (R–D) and rate-control performance than that of the state-of-the-art RC scheme implemented in the HEVC reference software HM11.0.     

基于运动特征的HEVC快速帧间预测编码研究

为了降低高效视频编码(HEVC,high efficiency v ideo coding)的帧间预测复杂度,提出了一种基于运动特征的HEVC快速帧间预测新方 法。首先利用视频相邻帧的时域相关性,通过计算 每个待编码单元(CU)及其子块的帧差离散度(FDD)确定该CU的最佳编码深度d ;再依据该深度下CU的区 域运动特征(RMF_d)将待编码CU划分为3类运动区域,进而确 定该CU的候选帧间预测模式,减少 不必要的帧间预测模式遍历过程。试验结果表明,本算法可以在保证编码性能损失不大的前 提下显著提高编码效率;与标准算法相比,在低延时和随机访问两种编码结构下,同等客观 质量下码率(BDBR)分别增加0.89% 和0.83%,同时节省了51.6%和48.5%的编码时间。     

Inter-layer correlation-based adaptive bit allocation for enhancement layer in scalable high efficiency video coding

To facilitate the diversity of network and end-user devices, bit allocation technology must be combined with scalable high efficiency video coding (SHVC) to achieve continuous bitrate variation. However, to date, the multilayer coding feature in SHVC has not been fully utilized. In this paper, a bit allocation algorithm is proposed for the enhancement layer in SHVC. The algorithm includes two parts: a bit allocation method for the initial frame and another for subsequent frames. The bit allocation method for the initial frame consists of a bit allocation factor model constructed based on investigation of the influence of the initial target bitrate on the overall coding performance. For the bit allocation of the subsequent frames, alternate GOP coding is designed and implemented to fully exploit the inter layer correlation. In addition, an adaptive frame layer bit allocation ratio model is deduced according to the rate distortion optimization theory. Experimental results show that the proposed algorithm can improve PSNR by 0.44 dB and 0.41 dB under low delay and random-access configurations, respectively, and achieve high bitrate control accuracy. The algorithm also outperforms the state-of-the-art algorithms in term of PSNR improvement.     

基于相似度的HEVC帧内低复杂度算法

针对高清视频编码(HEVC)标准帧内编码计算 复杂度过高的问题,提出了基于最大编码单元(LCU)相似度的 深度范围及率 失真代价阈值预测低复杂度算法。首先分析LCU相似性并将其量化,然后利用该量化变量概 率密度分布规律, 采用贝叶斯分类方法估计当前编码LCU深度范围;同时考虑到编码单元(CU)之 间相关性,自 适应设定率失真代价阈值,用以提前结束模式选择及继续分割过程:通过LCU编码深度范围 预测和率失真代 价阈值实现快速CU划分方案。实验结果表明,在性能几乎不变的情况下,本文算法较标准 编码算法编码 时间平均减少了39.55%,平均BDBR增加在1%以内,BD-PSNR仅降低了 0.03dB,在保持良好视频质量下有效降低了编码复杂度。     

Subband coding of image sequences at low bit rates

In this paper a low bit rate subband coding scheme for image sequences is described. Typically, the scheme is based on temporal DPCM in combination with an intraframe subband coder. In contrast to previous work, however, the subbands are divided into blocks onto which conditional replenishment is applied, while a bit allocation algorithm divides the bits among the blocks assigned for replenishment. A solution is given for the ‘dirty window’ effect by setting blocks to zero that were assigned to be replenished but received no bits. The effect of motion compensation and the extension to color images are discussed as well. Finally, several image sequence coding results are given for a bit rate of 300 kbit/s.     

Low complexity encoder optimization for HEVC

High Efficiency Video Coding (HEVC) improved the coding efficiency significantly. Compared to its predecessor H.264/AVC, it can provide equivalent subjective quality with more than 57% bit rate reduction. However, the improvement on coding efficiency is obtained at the expense of much more intensive computation complexity. In this paper, based on an overall analysis of computation complexity at the HEVC encoder, a low complexity encoder optimization scheme is proposed by reducing the number of available candidates for evaluation in terms of the intra prediction mode decision, early termination of coding unit (CU) splitting and adaptive reference frame selection. With the proposed scheme, the rate distortion optimization (RDO) technique of HEVC can be implemented in a low-complexity way for complexity-constrained encoders. Experimental results demonstrate that, compared with the original HEVC reference encoder implementation, the proposed optimization scheme can achieve more than 40% complexity reduction on average with coding performance degradation as only 0.43% which can be ignorable.     

基于感兴趣区域的HEVC压缩性能优化

根据人类视觉系统(HVS)对纹理复杂及运动区域具有较强感知度的特点,提出了一种基于感兴趣区域的高效率视频编码(HEVC)压缩性能优化算法.首先使用Sobel梯度检测算子和运动矢量分别检测纹理复杂区域和运动区域,把检测到的纹理复杂及运动区域定义为感兴趣区域;再对感兴趣区域分级,通过调整量化参数(QP),优化比特分配.实验结果表明,与HEVC标准算法相比,所提算法码率平均减少了15.29％,时间平均节省了11.38％.     

一种基于视频内容特征的LCU层码率控制算法

针对高效率视频编码LCU层码率控制方案对目标 比特分配不合理,图像复杂度综合 因子考虑不全导致率失真性能损失较大的问题,提出了一种基于视频内容特征的LCU层码 率控制算法。通过Scharr算子和Hadamard变换分别检测编码区域的纹理复杂度和能量分 布;对纹理复杂度因子和能量占比因子进行联合加权,构建了一种新的权重计算公式,用于 LCU层目标比特的优化分配,并进行模型参数的调整。实验结果表明,本文算法在低延迟B 配置和P配置下,与动态调整码率控制算法相比,比特率相对误差平均下降了0.011%和0.010%,率失真性能平均提高了2.5%。     

An image feature-based method to efficiently determine inter-coding depth in HEVC

The quad-tree based picture partition scheme in High Efficiency Video Coding (HEVC) results in a more substantial increase in computational complexity than those incurred by its predecessor video coding standards because of the need in this scheme to determine the best coding unit (CU) partitions. In this paper, we propose a method to effectively reduce the computational complexity of inter-prediction coding in the HEVC standard. The relative displacement of the largest coding unit (LCU) at the corresponding position between adjacent frames is tested through optical flow (motion estimation). The texture intensity of the LCU at the given time is tested if the condition that determines the coding depth in advance cannot be satisfied. The depth of the coding unit (CU) can be determined in advance beyond the xCompressCU function by using our proposed method, which does not require the calculation of the rate-distortion (RD) cost for each level of depth, and thus reduces the circular traversal times of the xCompressCU function. Experimental results proved that our proposed method is effective, as it reduced the computational complexity of an encoder by 53.2% on average, and had a slight influence on coding performance.     

3D Color Set Partitioning in Hierarchical Trees

This paper introduces the 3D color set partitioning in hierarchical trees (3D-CSPIHT) low bit rate embedded video coding scheme. The codec exploits the correlation between temporal and spatial wavelet coefficients and the interdependency between luminance and chrominance components to code color video sequences without the need for explicit bit allocation. Besides offering rate scalability, the new codec also produces multi-resolution scalable code streams. The hierarchical variable size block matching motion estimation technique is also integrated to demonstrate the motion estimation option with 3D-CSPIHT. The coding results show that 3D-CSPIHT produces better performance and visual quality compared to 3D-SPIHT.     

Piecewise DC prediction in HEVC

In this paper, we propose an improved DC prediction method for high-efficiency video coding (HEVC) intra coding. The technique involves the application of pixel-wise predictors rather than block-based predictor in the DC mode. In HEVC, the pixels of neighboring reconstructed blocks are used to support multiple directional spatial prediction modes and reduce spatial redundancy. For lossless coding, pixel-by-pixel differential pulse code modulation (DPCM) is applied to directional predictions. Consequently, residuals are reduced and coding efficiency is improved. Since DC prediction still employs block-based coding, pixel-wise DC prediction is needed for better coding efficiency. When compared to HEVC lossless intra coding, the proposed algorithm reduces the bit rate by 5.95%. Furthermore, with pixel-by-pixel DPCM, the average bit rate reduction is 10.64% when compared to HEVC lossless intra coding.     

多视点纹理加深度编码的联合码率控制方法

码率控制技术是多视点视频编码和传输中一个关键的问题。为了提高三维(3D)视频的整体显示质量,包括虚拟视点质量和编码视点质量,提出一种多视点纹理加深度编码的联合码率控制方法。该算法研究了纹理和深度的关系,采用基于模型方法确定最优的纹理和深度之间的码率比例。根据各个视点编码结果的统计规律,不同的视频序列采用不同的视点间比特分配比例。实验结果表明,与目前流行的多视点码率控制算法相比,该算法在计算复杂度基本保持不变的情况下,平均码率控制误差在0.6%以内,客观质量PSNR最高可提高0.65 dB。