基于多方向边界匹配的视频误码掩盖算法

视频压缩码流对于信道误码十分敏感,可能导致重建图像质量严重下降.误码掩盖技术利用图像在时间和空间上的相关性,可以有效地降低误码对视频图像的影响.文中提出了一种基于多方向边界匹配的时域误码掩盖算法.该算法能更精确地恢复错误宏块的运动矢量,从而获得比传统的时域掩盖算法更好的视频质量.     

信道自适应UEP技术在H.264视频通信系统中的应用

在进行基于H．264标准的视频通信系统设计时，为提高编码视频流的抗误码性能以及编码器的编码效率，提出了一种信道自适应非平等误码保护(UEP)技术。该技术可根据反馈的信道状态信息自适应地确定H．264编码视频流在网络适配层(NAL)中的工作模式，在丢包信道中结合人眼的视觉特性重新对编码视频信息进行分区并分别采用不同优先级的误码保护。仿真实验表明，在有效提高H．264视频通信系统中解码器输出重构视频图像视觉质量的同时，进一步降低编码器端数据包的打包开销，从而提高编码器的编码效率。     

一种用于H.264视频容错转码的帧内宏块刷新算法

无线网络信道具有误码率高、延时抖动等不稳定的特性。为了保证视频信息从有线网络到无线网络中传输的质量,需要对视频进行容错转码。基于H.264容错转码系统,利用转码结构中解码部分的运动矢量信息,自适应地在编码部分进行帧内刷新,以提高视频的抗误码能力。实验结果对比表明,该帧内刷新算法能够以较少的比特率为代价,有效地提高了接收端的视频质量。     

基于主观质量控制的数字视频综合抗误码技术

本文系统地提出了一套视频通信中的综合抗误码技术.本文针对窄带噪声信道,在H.263+编码的基础上,首先提出了视频主观质量控制策略;并在编码端根据视频信息的重要程度相应采用了非等重保护的前向纠错(FEC)算法,当恢复视频仍有误码时,则在解码端根据不同的帧编码类型使用相应的时/空误码掩盖方法提高恢复视频质量.计算机仿真结果表明,采用以视频主观质量控制策略为核心的综合抗误码技术,在高误码环境下,恢复视频信噪比可提高10-20dB,主观视频质量可提高1-2个等级.该综合抗误码方案已在实际中得到应用.     

H.264/AVC标准中基于CABAC的数字视频加密研究

分析和总结了用于新一代视频编码标准H.264／AVC加密的候选域，在此基础上提出了一种新的基于CABAC（基于上下文的自适应二进制算术编码）的数字视频加密方案，并给出了2种安全加密操作：RCME（规则编码模式加密）和BCME（旁路编码模式加密）实现了残差系数码字、运动矢量差码字和帧内预测模式的加密保护。实验结果表明，该方案具有较好的安全性、编码效率和误码顽健性。     

一种基于运动补偿三维小波的 多描述视频编码方法

 本文将多描述编码与运动补偿三维小波可扩展视频编码相结合,提出了一种基于运动补偿三维小波的多描述视频编码方法.该方法首先根据编码序列的运动特性,自适应地进行每个描述的码率分配,以控制各个描述中的冗余,然后将编码序列的关键信息-运动矢量和低频帧码流复制到两个描述中,并将高频帧码流分配到不同的描述中.在解码端根据正确接收信息的不同,采用不同的方法进行视频重建.实验结果表明,与单描述编码方法相比,在信道丢包率较高的情况下,本文方法可以提供更好的传输鲁棒性.     

一种基于多参考帧的时域误码掩盖算法

视频压缩码流对于信道误码十分敏感,可导致重建图像质量严重下降,在接收端就要使用误码掩盖技术对损坏的视频进行掩藏。文中提出一种基于多参考帧的时域误码掩盖算法,首先计算受损宏块的相邻块的运动矢量的均值,然后遍历所有参考帧得到待选的误码掩盖宏块,最后用外边界匹配算法找出替代受损宏块的宏块。研究结果表明,该算法能更精确地恢复错误宏块的运动矢量,从而获得比传统的时域掩盖算法更好的视频质量。     

用于地面数字电视系统的多级编码调制技术

在地面数字电视广播系统中,为了满足不同信道条件和不同接收设备的用户需要,提出了一种多级编码调制的方案.把广播数据分成多个优先级,使用多级编码调制和集分割映射技术,为不同优先级的数据提供不同的差错保护.解码时采用多阶段译码的方法,使得用户可以根据自身信道的质量或者接收设备的能力,获得相应的数据传输率.仿真结果表明,该方案在AWGN和多径信道下都具有较好的性能.     

一种基于联合信源信道自适应的不等错误保护方法

针对误码信道和信源编码的统计特性,提出了一种能有效提高基于DCT变换的视频编码码流的抗误码性能的自适应不等错误保护方法.它基于信道误码的反馈信息,选择DCT的量化参数q和信道编码码率,并进行DCT重排和VLC编码,再对数据流进行不等差错保护.通过实验证明,它在高误码信道中性能优于EEP等.     

用基于运动的区域生长法分割序列图像

针对基于对象的视频编码应用,提出了一种基于运动的区域生长分割方案,将图像分割成具有一致运动特征的区域。方案中采用块匹配法进行运动估计,利用重构式开－闭及区域生长型水岭算法等形态工具进行空间域分割,以改进时间域分割。此外,为了求取可靠的运动矢量,还提出了一种变化检测算法及预选多个候选运动矢量的运动估计方法。初步的模拟结果表明,该方案是可行的。其主要优点是算法简单、计算量少。     

一种空间域Wyner-Ziv视频编码系统的性能改进算法

分布式视频编码是建立在Slepian-Wolf和Wyner-Ziv信息编码理论基础上的全新视频编码框架,具有编码复杂度低,编码效率较高,抗误码性能好的特点.本文首先简单介绍了一种典型的分布式视频编码实现方案——空间域Wyner-Ziv视频编码,随后提出一种空间域Wyner-Ziv视频编码系统的性能改进算法,该算法在不增加编码复杂度的基础上,在解码端利用双向运动估计预测获取更高质量的边信息,同时采用基于Huber-Markov随机场约束的联合迭代解码算法重建图像.实验结果表明,在相同的输出码流情况下,本文改进算法在解码端重建图像的峰值信噪比与空间域Wyner-Ziv视频编码算法相比平均提高2dB,并且主观效果有所改善.     

Data partitioning and coding of DCT coefficients based on requantization for error-resilient transmission of video

In this paper, we propose an efficient data partitioning and coding algorithm for an error-resilient transmission of DCT coefficients in error prone environment. In the typical data partitioning for Inter-coded frames, motion and macroblock header information is separated from the texture information. It can be an effective tool for the transmission of video over the error prone environment. For Intra-coded frames, however, the loss of DCT coefficients is fatal because there is no other information to reconstruct the corrupted macroblocks by errors. Conventional data partitioning algorithm for DCT coefficients is to separate a fixed number of the significant DCT coefficients from the remaining coefficients, called the spectral separation. While the spectral separation can guarantee an error resilient transmission with small overhead, the main drawback is a significant decrease in the image quality of the high priority partition, compared with that of the bitstreams without data partitioning for an equivalent bit-rate. In the proposed scheme, the quantized DCT coefficients are partitioned into an even-value approximation and the odd remainder part. We also propose a simple and efficient coding algorithm for the odd remainder part. It is shown that the proposed algorithm provides a better image quality than the conventional methods with a little overhead.     

H.264 error resilience coding based on multi-hypothesis motion-compensated prediction

In this paper, we propose efficient schemes for enhancing the error robustness of multi-hypothesis motion-compensate predictive (MHMCP) coder without sacrificing the coding efficiency significantly. The proposed schemes utilize the concept of reference picture interleaving and data partitioning to make the MHMCP-coded video more resilient to channel errors, especially for burst channel error. Besides, we also propose a scheme of integrating adaptive intra-refresh into the proposed MHMCP coder to further improve the error recovery speed. Extensive simulation results show that the proposed methods can effectively and quickly mitigate the error propagation and the penalty on coding efficiency for clean channels due to the inserted error resilience features is rather minor.     

An efficient motion vector coding scheme based on minimum bitrateprediction

Motion vector coding efficiency is becoming an important issue in low bitrate video coding because of its increasing relative bit portion. This work presents a new motion vector coding technique based on minimum bitrate prediction. In the proposed scheme, a predicted motion vector is chosen from the three causal neighboring motion vectors so that it can produce a minimum bitrate in motion vector difference coding. Then the prediction error, or motion vector difference (MVD), and the mode information (MODE) for determining the predicted motion vector at a decoder are coded and transmitted in order. Sending bits for the MVD ahead of bits for the MODE, the scheme can minimize the bit amount for the MODE by taking advantage of the fact that the minimum bitrate predictor is used for motion vector prediction. Adaptively combining this minimum bitrate prediction scheme with the conventional model-based prediction scheme, more efficient motion vector coding can be achieved. The proposed scheme improves the coding efficiency noticeably for various video sequences.     

基于MPEG压缩域的快速、鲁棒的全局运动信息提取方法

全局运动信息在视频分析中起着重要的作用.本文根据MPEG编码特点,提出了一种从MPEG压缩域中快速有效地进行全局运动参数估计的算法.该算法充分利用了MPEG压缩码流中的信息,通过提取预测残差DC图像的运动背景区域,估计全局运动参数,从而保证了参数估计的准确性,有效地克服了已有文献中仅仅采用运动矢量进行全局运动估计的局限性.根据不同的MPEG测试序列的对比分析,结果表明,本算法可快速准确地对MPEG视频序列进行全局运动信息估计,同时具有很高的鲁棒性.     

自适应量化索引调制及其信道编码的信息隐藏技术的研究

在信息隐藏通信时,对JPEG-2000小波多级分解并在嵌入块编码中根据不同级的LL-HH分组系数引入自适应量化索引调制(AQIM),同时结合信道编码技术可以有效地实现指纹节点数据的信息隐藏和安全传输技术.通过实验可知,低码率时,与QIM隐藏技术相比,本系统有效地提高了恢复指纹图像的PSNR,同时降低了系统的BER,表明该系统恢复的图像具有更好的感官质量和更强的鲁棒性.     

基于水印技术的MPEG-4形状错误隐藏

MPEG-4编码是一种基于对象内容的第二代视频编码方案,将视频根据内容分割成前景对象和背景。视频对象的信息分为形状信息、纹理信息和运动信息,而形状信息是正确解码视频对象的基础。本文就是针对MPEG-4编码标准中的I-VOP的形状信息的错误进行的错误隐藏。采用的方法有别于传统的曲线插值方法和马尔可夫域最大后验估计方法,首次采用基于鲁棒盲水印的算法,主要是将形状信息或变化作为水印信息嵌入到背景对象中。针对前人提出的方法只能修补小部分的损失,本文对于形状信息严重丢失的修复效果很好。     

Error concealment techniques for digital TV

Compressed video bitstreams are intended for real-time transmission over communication networks. Most of the video coding standards employ the temporal and spatial prediction structure to reduce the transmitted video data. Therefore, the coded video bitstreams are highly sensitive to information loss and channel errors. Even a single bit error can lead to disastrous quality degradation in both time and space. This quality deterioration is exacerbated when no error resilient coding mechanism is employed to protect coded video data against the error prone environments. Error concealment is a data recovery technique that enables the decoder to conceal effects of transmission errors by predicting the lost or corrupted video data from the previously reconstructed error-free information. Motion vector recovery and motion compensation with the estimated motion vector is a good approach to conceal the corrupted macroblock data. In this paper, we develop various error concealment algorithms based on motion vector recovery, and compare their performances to those of conventional error concealment methods.     

Motion and texture rate-allocation for prediction-based scalable motion-vector coding

Modern video coding applications require data transmission over variable-bandwidth wired and wireless network channels to a variety of terminals, possibly having different screen resolutions and available computing power. Scalable video coding technology is needed to optimally support these applications. Recently proposed wavelet-based video codecs employing spatial-domain motion-compensated temporal filtering (SDMCTF) provide quality, resolution and frame-rate scalability while delivering compression performance comparable to that of H.264, the state-of-the-art in single-layer video coding. These codecs require quality-scalable coding of the motion vectors to support a large range of bit-rates with optimal compression efficiency. In this paper, the practical use of prediction-based scalable motion-vector coding in the context of scalable SDMCTF-based video coding is investigated. Extensive experimental results demonstrate that, irrespective of the employed motion model, our prediction-based scalable motion-vector codec (MVC) systematically outperforms state-of-the-art wavelet-based solutions for both lossy and lossless compression. A new rate-distortion optimized rate-allocation strategy is proposed, capable of optimally distributing the available bit-budget between the different frames and between the texture and motion information, making the integration of the scalable MVC into a scalable video codec possible. This rate-allocation scheme systematically outperforms heuristic approaches previously employed in the literature. Experiments confirm that by using a scalable MVC, lower bit-rates can be attained without sacrificing motion-estimation efficiency and that the overall coding performance at low rates is significantly improved by a better distribution of the available rate between texture and motion information. The only downside of scalable motion-vector coding is a slight performance loss incurred at high bit-rates.