面向HBP编码格式的立体视频B帧整帧丢失分层错误隐藏算法

针对分层B帧(HBP)编码格式的立体视频B帧整帧丢失的问题,该文分析了双视点视频中存在的视点间运动矢量相关性,提出一种分层错误隐藏算法。该算法与当前主流的方法有两大不同:一是该算法采用分级隐藏,根据B帧的重要性等级不同采用不同的错误隐藏方法;二是该算法考虑了相邻视点序列之间的宏块运动矢量相关性。实验表明,该算法的性能优于当前常用的H.264多视点视频整帧丢失错误隐藏方法。     

视频错误掩盖技术进展

针对2005年到2015年基于H.264/AVC编码标准下的图像错误掩盖技术的发展状况,根据不同类型的编码帧采用的不同掩盖技术,归纳分类了当前已有算法,分析总结了基于传统的错误掩盖技术,即时域掩盖、空域掩盖和时空域结合的掩盖,包括基于场交织的错误掩盖与数字水印技术相结合的错误掩盖,以及基于三维视频的错误掩盖,比较了各算法的优势和局限性,并讨论了其未来发展趋势.     

A content-adaptive sharpness enhancement algorithm using 2D FIR filters trained by pre-emphasis

This paper proposes a content-adaptive sharpening algorithm using two-dimensional (2D) FIR filters trained by pre-emphasis for various image pairs. In the learning stage, all low-quality (LQ) and high-quality (HQ) image pairs are first pre-emphasized, i.e., properly sharpened. Then selective 2D FIR filter coefficients for high-frequency synthesis are trained using the pre-emphasized LQ–HQ image pairs, and then are stored in a dictionary that resembles an LUT (look-up table). In the inference stage, each input image is pre-emphasized in the same manner as in the learning stage. The best-matched 2D filter for each LQ patch is then found in the dictionary, and an HQ patch corresponding to the input LQ patch is synthesized using the resultant 2D FIR filter. The experiment results show that the proposed algorithm visually outperforms existing ones and that the mean of absolute errors (MAEs) and MSSSIM (multi-scale structure similarity) of the proposed algorithm are about 10% to 60% lower and about 0.002–0.053 higher, respectively than those of the existing algorithms.     

Joint reference frame inter-mode selection for fast H.264 video coding

The H.264/AVC video coding standard uses multiple reference frames and variable-size macroblock partitions in inter-prediction. This flexibility allows the standard to achieve excellent rate-distortion performance at the cost of high encoding complexity. We present an algorithm for fast joint selection of the reference frames and macroblock partitions in rate-distortion-based coding. Experimental results for eight standard test video sequences show that, compared with exhaustive search, our algorithm can save up to 74.9 % of the encoding time with negligible loss in rate-distortion performance. The presented algorithm is also evaluated using a subjective assessment metric; quality evaluation measures based on user satisfaction. Diverse types of video sequences were used with different frame rates, quantization parameters, and resolutions. The effects of changing bit rate and resolution on compression efficiency and viewers’ satisfaction are also presented. Results show that our algorithm provides high scores of perceptual satisfaction that are significantly affected by the compression technique. As a result, we claim that our algorithm presents original and significant enhancement compared with exhaustive search. In addition, overall test results showed that our technique outperformed three of the best previously proposed methods and gave higher viewer satisfaction.     

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。     

H.263编码视频流的混合错误掩盖

当H．263编码视频流在因特网上传输时，易受错误的影响，错误不但会影响当前帧还会继续扩散到以后的解码帧，从而导致图像质量的严重恶化，目前消除错误影响的常用算法是空域掩盖和时域掩盖算法，但是单纯地使用空域算法会造成图像的钝化，而时域算法则无法处理大运动的图像区域，因此，建议了一种时域和空域混合掩盖算法，同时使用两类算法对发生错误的图像帧进行掩盖。模拟结果显示该算法能够达到可以接受的图像质量，适应于视频会议、远程教育等应用的要求。     

基于HEVC帧内预测的复杂度控制

帧内预测在视频编码中是非常重要的模块.在视频实时编码与传输过程中,场景切换会经常出现.此时,一般会采用全Ⅰ帧编码.研究发现,即使是全Ⅰ帧编码,也往往会非常耗时.基于编码单元深度范围和帧内预测中候选预测方向个数研究了HEVC编码器的复杂度控制问题.针对不同的目标编码复杂度,算法自适应地选择不同的方法来优化编码过程.实验结果表明,该算法在保证视频质量的前提下实现了对不同复杂度目标的控制.     

Flash scene video coding using weighted prediction

A novel algorithm for coding flash scenes is proposed. In principle, flash scenes can be detected by analyzing the histogram differences between frames. The proposed algorithm then suggests an adaptive coding order technique for increasing the efficiency of video coding by taking account of characteristics of flash scenes in video contents. The use of adaptive coding technique also benefits to enhance the accuracy of derived motion vectors for determination of weighting parameter sets. Experimental results show that a significant improvement of coding performance in terms of bitrate and PSNR can be achieved in comparison with the conventional weighted prediction algorithms.     

Four-dimensional matrix Walsh transform for lossless compression of color video

This article presents a coding method for the lossless compression of color video.In the proposed method,four-dimensional matrix Walsh transform(4D-M-Walsh-T)is used for color video coding.The whole n frames of a color video sequence are divided into '3D-blocks' which are image width(row component),image height(column component),image width(vertical component)in a color video sequence,and adjacency(depth component)of n frames(Y,U or V)of the video sequence.Similar to the method of 2D-Walsh transform,4D-M-Walsh-T is 4D sub-matrices,and the size of each sub-matrix is n.The method can fully utilize correlations to encode for lossless compression and reduce the redundancy of color video,such as adjacent pixels in one frame or different frames of a video at the same time.Experimental results show that the proposed method can achieve higher lossless compression ratio(CR)for the color video sequence.     

Joint Source/Channel Coding Based on Two‐Dimensional Optimization for Scalable H.264/AVC Video

The scalable extension of the H.264/AVC video coding standard (SVC) demonstrates superb adaptability in video communications. Joint source and channel coding (JSCC) has been shown to be very effective for such scalable video consisting of parts of different significance. In this paper, a new JSCC scheme for SVC transmission over packet loss channels is proposed which performs two‐dimensional optimization on the quality layers of each frame in a rate‐distortion (R‐D) sense as well as on the temporal hierarchical structure of frames under dependency constraints. To compute the end‐to‐end R‐D points of a frame, a novel reduced trellis algorithm is developed with a significant reduction of complexity from the existing Viterbi‐based algorithm. The R‐D points of frames are sorted under the hierarchical dependency constraints and optimal JSCC solution is obtained in terms of the best R‐D performance. Experimental results show that our scheme outperforms the existing scheme of [13] with average quality gains of 0.26 dB and 0.22 dB for progressive and non‐progressive modes respectively.     

分布式压缩视频编码的帧分类重构方法研究

在很多的应用场景中需要具有低复杂度的视频编码器,新兴的分布式视频编码和压缩感知技术正好适用于这些场景中,因而出现了一种新的视频编码方案——分布式压缩视频编码。在现有的一些分布式压缩视频编码方案中,视频帧在编码端是独立编码,在解码端进行联合解码,具体来说就是关键帧独立解码,非关键帧在由关键帧生成的边信息的帮助下进行解码,这就忽略了非关键帧之间的相关性。本文提出一个新的分布式视频编码方案,将非关键帧分为主非关键帧和次非关键帧,主非关键帧利用关键帧生成地边信息进行解码,而次非关键帧先利用相邻的主非关键帧进行观测值预测,然后再利用关键帧生成的边信息进行解码。实验结果表明,在本文提出的框架下,非关键帧的重构质量提高了有2dB~4dB。      

A DCT/DST-based error propagation-free data hiding algorithm for HEVC intra-coded frames

Currently, two error propagation-free discrete cosine transform (DCT)-based data hiding algorithms, one by Ma et al. and the other by Lin et al., were presented for H.264/AVC intra-coded frames. However, the state-of-the-art video codec, high efficiency video coding (HEVC), adopts both integer DCT and discrete sine transform (DST) such that the previous DCT-based algorithms cannot fully utilize available capacity for data hiding in HEVC. This paper presents the first DCT/DST-based data hiding algorithm for HEVC intra-coded frames where the block DCT and DST coefficient characteristics are investigated to locate the transformed coefficients that can be perturbed without propagating errors to neighboring blocks. Experimental results confirm the merits of the proposed algorithm in providing the intra-frame error propagation-free advantage, the quality improvement for marked images, the compression power inherited from HEVC, and the superiority of embedding capacity for low bitrate coding when compared with the previous two algorithms for H.264/AVC.     

Fast transmission distortion estimation and adaptive error protection for H.264/AVC-based embedded video conferencing systems

This paper presents the design and implementation of an error-resilient H.264/AVC-based embedded video conferencing scheme over Internet. We first develop a fast recursive algorithm to estimate the decoder-side distortion of each frame in the presence of packet loss. The algorithm operates at block level, and considers the impacts of different intra prediction modes, the unrestricted intra prediction, and the skip mode. We then design a family of very short systematic forward error correction codes with linear encoding and decoding complexity, which runs across the slices of each frame to recover lost packets. An optimization problem is then formulated to minimize the decoder-side distortion by allocating a given channel coding redundancy among a group of frames. Various techniques are introduced to speed up the algorithm without sacrificing too much accuracy, in order to meet the hardware and real-time constraints of the system. As a result, the proposed scheme can run on a real-time embedded video conferencing system with resolution up to 1024×576 pixels, 30 frames per second (fps) and 4 megabits per second (Mbps).     

VLC table prediction for CAVLC in H.264/AVC using correlation,statistics, and structural characteristics of mode information

The H.264/AVC video coding standard adopted context-based adaptive variable length coding (CAVLC) as an entropy coding tool. By combining adaptive variable length coding (VLC) with context modeling, we can achieve a high coding performance. However, CAVLC in H.264/AVC has the problem that VLC table prediction is not always accurate. In this paper, we propose a new VLC table prediction algorithm using the correlation between coding modes of the current and neighboring sub-blocks and the statistics of mode distribution in both intra and inter frames. In addition, we can further increase correctness of VLC table prediction considering the structural characteristics of mode information in inter frames. Experimental results show that the proposed algorithm increases correctness of VLC table prediction by 10.07% and reduces the bit rate by 1.21% on average without significant increment of encoding time.     

用于视频对象平面生成的运动对象自动分割

新的视频编码标准MPEG-4具有基于内容的功能。它把图像序列分解成视频对象平面(VOP),每个VOP代表一个运动对象。文中提出了一种提取运动对象的新的视频序列分割算法,算法的核心是一个对象跟踪器,它利用Hausdorff距离将对象的二维二值模型与后续帧进行匹配,然后采用一种新的基于运动相连成分的模型刷新方法对模型的每一帧进行刷新。初始的模型自动产生,再利用滤波技术滤除静止背景,最后,利用二值模型从序列中提取出VOP。     

一种基于分层B帧架构的高效比特分配算法

随着分层B帧码率控制技术在SVC(可伸缩视频编码)中的广泛应用,视频编码的质量得到了很大提高,然而传统的H.264码率控制技术并未将B帧的比特分配考虑在内。提出一种基于分层B帧架构自适应调节B帧比特分配的码率控制算法,该算法研究了基于同一个图像组(GoP)中各时域层权重因子的自适应调节,为各时域层分配不同的目标比特;同时基于同一个时域层中各帧复杂度的不同,为各帧分配不同的目标比特。实验结果表明,与目前流行的分层B帧码率控制算法相比,该算法在比特控制误差并未降低的情况下,客观质量PSNR可提高0.1～0.4 dB。     

GOP-based channel rate allocation using genetic algorithm for scalable video streaming over error-prone networks.

In this paper, we address the problem of unequal error protection (UEP) for scalable video transmission over wireless packet-erasure channel. Unequal amounts of protection are allocated to the different frames (I- or P-frame) of a group-of-pictures (GOP), and in each frame, unequal amounts of protection are allocated to the progressive bit-stream of scalable video to provide a graceful degradation of video quality as packet loss rate varies. We use a genetic algorithm (GA) to quickly get the allocation pattern, which is hard to get with other conventional methods, like hill-climbing method. Theoretical analysis and experimental results both demonstrate the advantage of the proposed algorithm.     

Proposed dynamic error control techniques for QoS improvement of wireless 3D video transmission

Error control techniques like error resilience (ER) and error concealment (EC) are efficient techniques to ameliorate the lost macroblocks (MBs) in the 3D video (3DV) communication system. In this paper, we propose efficient and adaptive hybrid ER‐EC algorithms for 3DV transmission over error‐prone wireless channels. At the encoder, adaptive preprocessing ER mechanisms are proposed through using the context adaptive variable length coding entropy, slice structured coding modes, and explicit flexible macroblock ordering mapping. They are used to assist the suggested EC techniques at the decoder to accurately reconstruct the erroneous MBs and frames. At the decoder, an efficient postprocessing EC technique with multiproposition methods is proposed to dynamically select the convenient EC hypothesis method based on the size of the lost MBs, the faulty view, and the frame type. It conceals the received erroneous MBs of intra‐encoded and inter‐encoded frames of the transmitted 3DV by exploiting the temporal, spatial, and inter‐view correlations among frames and views. To further improve the decoded 3DV quality, a weighted overlapping block motion and disparity compensation technique is used to reinforce the performance of the suggested ER‐EC techniques. Experimental results on various 3DV streams prove that the suggested techniques have considerably acceptable subjective and objective 3DV performance. They achieve an improved average peak signal‐to‐noise ratio gain by almost 2.85 dB compared to the conventional error control algorithms at a packet loss rate = 40%.