Content-based scalable H.263 video coding for road traffic monitoring

For sending video data through very low bit-rate mobile channels, video codec with high compression rate is the pre-requisite. Although the H.263 video codec is recommended as one of the candidates due to its simplicity and efficiency, it is generally believed that its compression efficiency can be further improved if the content-based scalable video coding technique can be applied. In this paper, we propose a modified H.263 encoder which supports real-time content-based scalable video coding. The proposed technique is applied to real-time video surveillance systems for road traffic monitoring. For the proposed approach, the moving objects, i.e. cars, are first extracted from the steady background. Their activities are then further classified as fast or slow by assessing the regularity of their motion. The information is then passed to a modified H.263 encoder to reduce the temporal and spatial redundancies in the video. As compared with the conventional H.263 encoder using for the same application, the proposed system has a 20% increase in compression rate with negligible visual distortion. The proposed system fully complies with the ITU H.263 standard hence the encoded bit stream is completely comprehensible to the conventional H.263 decoder.     

H.263自适应量化和可变长编码的最优化设计

该文首先概述了低码率图象编码标准H．263,然后着重讨论了自适应量化以及Huffman编码的联合优化设计,其中包括算法设计流程和相应的实现代码,最后给出了有关的实验结果和分析,结果表明该算法能有效地加快编码和解码器的运行速度,同时又能保证一定的图象质量。     

多解析度自适应零块判决算法

在视频会议等应用中,视频编码的速度是保证系统实时性的关键.为了减小视频编码的运算量并提高系统的整体性能,提出了多解析度的自适应零块发现判决算法.多解析度通过对图像的子采样从而大幅度降低了搜索最佳匹配块的次数;而自适应的零块判决算法使得运动搜索速度收敛的更快,在不影响图像质量的前提下提高了编码的效率,并且减少了后续模块(DCT、量化等)所占用的时间.利用H.263算法进行了测试,结果显示在图像主客观质量基本不变的前提下,编码时间最多减少了近40%.     

一种频域块匹配+预判全零系数的运动估计算法

用 H.2 63标准对低码率图像编码时 ,编码器的复杂性主要取决于运动估计、离散余弦变换等运算 ,为了减少编码器的运算量、提高编码速度 ,提出一种有效的频域块匹配 +预判全零系数的运动估计算法。这种算法充分利用离散余弦变换的特点 ,在频域内使用块匹配法进行运动估计 ,并将预判全零系数和运动搜索相结合。实验表明该算法不仅可以有效地提高编码速度 ,而且可以较好地保持 H.2 63高压缩比及运动图像的质量等特性。本文用该算法研制了甚低码率视频编码器的软件 ,该软件编码器可以在 PSTN上实现实时编解码 ,具有较大的使用价值。     

视频编码中考虑模式选择的位率优化控制

本文在传统位率控制方法的基础上提出一种新算法,即基于宏块的最佳位率控制算法．主要思想是在考虑还宽,比特率和缓冲区大小的同时,考虑不同宏块模式的选择对位率的影响,文中给出了一些相关结果并将其与传统方法所得数据相比较,结果表明在多数位率条件下用本算法得到的ＰＳＮＲ比传统方法要好．     

结合H.263与SLCCA的新的极低比特率小波视频编码

小波对于静止图像编码取得了巨大成功,但对于视频编码只有少数较为成功的尝试,提出一种针对极低比特率应用的新的结合H.263与SLCCA的混合小波视频编码算法,在提出的算法中,首先,用基于H.263的微调运动估计减少时间冗余,用无遗漏覆盖块运动补偿保证运动补偿误差帧的连续性;第2,对运动补偿误差帧进行小波变换得到全局能量压缩;第3,用SLCCA组织和表示小波变换后的数据;最后,运动向量的水平和垂直分量分别用自适应算法编码,算法在A级测试序列Akiyo和B级测试序列Foreman（QCIF）上测试取得了良好效果。     

基于TMDSP开发平台的实时视频编解码系统设计与实现

本文在研究低比特率视频编解码算法的基础上 ,以 h.2 6 3协议为标准 ,以 Philips公司的 TMDSP卡为开发平台 ,实现了一种视频编解码系统 ,经过测试该系统在对 qcif格式图像同时编码解码时 ,能达到每秒 2 5帧以上 ,平均码率能控制在 4 0 kbps以下 ,该压缩卡能广泛应用于可视电话、图像监控、视频会议等多媒体应用中     

基于整数变换的全零块判决方法

H．263中的运动搜索和变换域编码是运算量很大的部分，也是影响系统实时性能的瓶颈，为了减少图像编码的运算量，在采用整数变换代替浮点DCT变换的基础上，提出了一种全局判决方法，即在运动搜索中和变换前进行全零块判决。该方法是根据整数变换和量化结果为零的特点，在运动搜索中，对差值块先进行全零块判决，如果找到全零块，就停止搜索，以省却以后的搜索运算和全零块的整数变换以及相应的量化运算，由于其可在基本保持H．263原有编码算法图像质量的同时，减少运算量和缩短码流，从而大幅度提高了编码器的编码效率。     

Multiresolution,perceptual and vector quantization based video codec

This paper presents a novel Multiresolution, Perceptual and Vector Quantization (MPVQ) based video coding scheme. In the intra-frame mode of operation, a wavelet transform is applied to the input frame and decorrelates it into its frequency subbands. The coefficients in each detail subband are pixel quantized using a uniform quantization factor divided by the perceptual weighting factor of that subband. The quantized coefficients are finally coded using a quadtree-coding algorithm. Perceptual weights are specifically calculated for the centre of each detail subband. In the inter-frame mode of operation, a Displaced Frame Difference (DFD) is first generated using an overlapped block motion estimation/compensation technique. A wavelet transform is then applied on the DFD and converts it into its frequency subbands. The detail subbands are finally vector quantized using an Adaptive Vector Quantization (AVQ) scheme. To evaluate the performance of the proposed codec, the proposed codec and the adaptive subband vector quantization coding scheme (ASVQ), which has been shown to outperform H.263 at all bitrates, were applied to six test sequences. Experimental results indicate that the proposed codec outperforms the ASVQ subjectively and objectively at all bit rates.     

Region-based rate control and bit allocation for wireless video transmission

In this paper, we propose a joint source-channel region-based rate control algorithm for real-time video transmissions over wireless systems. During the video transmission, the channel throughput available to the video encoder in the wireless systems is inherently variable, due to the retransmission of the error packets using the automatic repeat request (ARQ) error control. The variable data rate of the wireless system is characterized by the packet-level Gilbert two-state Markov Model, the parameters of which are extracted from the statistical properties of the channel information obtained from the wireless channel simulator. The proposed algorithm adopts a fast but effective block-based segmentation method to extract the regions of interest. Unlike traditional bit allocation methods used in the region/content-based rate control, the algorithm exploits the most effective criteria "coding qualities" as quantitative factors to directly control bit allocation among different regions so as to achieve better visual quality in the regions of interest. The computational complexity of the algorithm is low making it suitable for real-time applications. Compared with the MPEG-4 rate control algorithm, our algorithm can effectively enhance the perceptual quality for the regions of interest and significantly reduce the number of frame skipping; thereby, improve the smoothness of the video.     

H．264／AVC解码器优化的研究

视频编码新标准H．264／AVC与先前的标准如MPEG2、H．263、MPEG4第2部分相比，虽具有更高的编码效率和差错鲁棒性，但是这些编码效率的提高是以增加编码器和解码器的复杂度为代价的。研究表明，由于H．264／AVC编解码器的计算复杂度比其他视频压缩标准高出几倍甚至十几倍，因此实现实时编解码器需要寻找高效的优化方法。为了对解码器进行优化，从软件和硬件平台的角度提出了一种解码器的优化方法，最后进行了实验，实验结果显示，优化后的软件解码器能够达到实时解码。     

Vector-quantization-based video codec for software-only playback on personal computers

This paper discusses a video compression and decompression method based on vector quantization (VQ) for use on general purpose computer systems without specialized hardware. After describing basic VQ coding, we survey common VQ variations and discuss their impediments in light of the target application. We discuss how the proposed video codec was designed to reduce computational complexity in every principal task of the video codec process. We propose a classified VQ scheme that satisfies the data rate, image quality, decoding speed, and encoding speed objectives for software-only video playback. The functional components of the proposed VQ method are covered in detail. The method employs a pseudo-YUV color space and criteria to detect temporal redundancy and low spatial frequency regions. A treestructured-codebook generation algorithm is proposed to reduce encoding execution time while preserving image quality. Two separate vector codebooks, each generated with the treestructured search, are employed for detail and low spatial frequency blocks. Codebook updating and sharing are proposed to further improve encoder speed and compression.     

基于H．264的立体视频右图像整帧丢失错误隐藏算法

当H．264编码立体视频流在Internet上传输时，由于信道错误所引起的数据丢失常常会造成整帧图像的丢失。为了恢复丢失的整帧立体视频右图像，提出了一种基于H．264的立体视频右图像整帧丢失错误隐藏算法，该算法依据立体视频编码特点进行相关性分析，首先确定丢失帧中每个宏块的预测方式，然后采用运动补偿或视差补偿对其进行恢复，进而重现丢失帧。实验结果表明，该算法能够在较低的计算复杂度下，获得较高质量的立体视频图像。     

一种对残养帧的四叉树分解编码算法

为了克服在低比特率下的块效应,并适应实时编、解码的需要,提出了一种对残差帧的四叉树编码算法,该算法首先采用OBMC的方法生成预测帧以有效消除块效应,并针对残差帧的统计与视觉特性,对每个2×2的小块取灰度平均值作为最小编码单位,然后用四叉树分解方法来大致标记均值大于某阈值的块的位置,并以标量量化和自适应算术编码器编码其灰度值.与基于变换的编码方法相比,该算法简单、高效,码率低,解码质量高,是一种实时的编、解码算法.     

基于H.26L关键算法模块软件编码器的设计与实现

继制定了H.261、H.263、H.263+等视频压缩标准后,ITU—T正在制定新的视频压缩标准H.26L,目的是为了取得更加有效的图像压缩效果和提供理想的传输接口。文章首先分析了H.26L的各个关键算法模块的原理,与H.263、H.263+进行比较分析,得出其优点;然后阐述如何用VisualC++6.0实现这些算法模块;最后通过实验证明,该文设计的软件编码器能达到更高效的压缩比、信噪比和编码速度,具有一定的实用价值。     

基于Lagrange的H．264率失真编码优化算法

为了进一步提高编码速度，促进视频编码技术在多媒体通信领域的实际应用，本文对率失真视频编码的关键算法进行了深入的研究并提出了其优化方法，并从信息论理论出发，着重围绕图像压缩的理论，利用率失真特征数学模型、拉格朗日乘子法，对目前新一代的H．264视频标准进行编码算法模式选择，试图从最根本的理论角度探讨信源编码，以便得到更高的压缩比、更好的图像质量和更快的编码速度。最后，利用本文提出的编码模式优化算法，对H．264的JM61e（JUT Test Model）系统测试模型的性能进行全面测试。     

H.26L中新的帧内预测技术研究

H.26L是ITU-T制定的新一代视频编码国际标准。H.26L在以往的编码标准的基础上采用了新的帧内预测技术,减少了预测误差,改善了图像质量。文章重点分析了H.26L中新的帧内预测技术,包括不同大小的亮度分量预测算法和色度分量预测算法等,并与H.263+中的帧内预测模式进行对比分析,阐明了H.26L的优点,证明其具有比H.263+更佳的预测效果。     

基于非抽样小波字典的低速率视频编码

目前,大多数视频编码器所采用的核心编码技术都是基于分块DCT(discreted cosine transform)变换对帧预测误差进行编码,在极低编码速率下,这类编码器往往会产生人眼敏感的方块效应.而基于匹配跟踪冗余信号分解的视频编码器具有比H.263编码器更高的编码性能,但由于该算法需要在一个冗余字典里搜索最佳匹配误差结构的原子函数,其实现所需要的运算量比传统的编码器要高很多,因此影响了这种编码器的效率.提出了基于树形结构的非抽样小波字典的匹配跟踪算法,能够充分利用字典函数之间存在的滤波结构关系,使得整个算法实现的计算量显著下降.同时,考虑到相邻帧运动信息的连续性,最后还给出一种基于晶格结构的有效原子位置信息编码方法.实验结果表明,该算法保持了原有的编码性能,在视频编码应用中具有很好的实用价值.     

Statistical motion learning for improved transform domain Wyner-Ziv video coding

Wyner-Ziv (WZ) video coding is a particular case of distributed video coding (DVC), the recent video coding paradigm based on the Slepian-Wolf and Wyner-Ziv theorems which exploits the source temporal correlation at the decoder and not at the encoder as in predictive video coding. Although some progress has been made in the last years, WZ video coding is still far from the compression performance of predictive video coding, especially for high and complex motion contents. The WZ video codec adopted in this study is based on a transform domain WZ video coding architecture with feedback channel-driven rate control, whose modules have been improved with some recent coding tools. This study proposes a novel motion learning approach to successively improve the rate-distortion (RD) performance of the WZ video codec as the decoding proceeds, making use of the already decoded transform bands to improve the decoding process for the remaining transform bands. The results obtained reveal gains up to 2.3 dB in the RD curves against the performance for the same codec without the proposed motion learning approach for high motion sequences and long group of pictures (GOP) sizes.