三维小波变换结合运动补偿的视频编码器

对三雏小波变换结合运动补偿的视频压缩算法提出了改进方案。针对运动补偿提升（MCLIFT）框架的弱点,结合MPEG的特点,采用新的帧结构对视频序列进行帧间滤波去除时间冗余,再对每个帧在空间上进行小波分解并用SPIHT算法对小波系数进行编码。实验表明,此方法继承了MCLIFT框架的优点,同时又减少了时延和所需的帧缓存,而且这种与MPEG相似的帧结构能进一步降低码率,提高压缩比。     

基于ROI区域的极低比特率编码算法

在极低比特率视频编码算法中,对感兴趣区域(ROI)优先进行编码能够获得更好的重建图像质量.在本文中,我们讨论了一种基于彩色直方图的人脸跟踪技术,它能够在头肩像图像序列中简单有效的准确定位ROI区域(人脸区域),并且,本文还提出了一种被称为小波块集合划分(SPWB)的小波编码算法用来对视频序列进行帧内编码,编码试验的结果表明,在同样的压缩比下,SPWB编码器能够获得比H.26L帧内编码器更好的重建图像质量.     

基于多小波域新型空间方向树的SPIHT改进算法

为了更好地利用图像多小波域系数的相似性进行编码,提出了一种基于多小波域新型空间方向树的SPIHT改进算法。在SPIHT改进算法中首先定义了一种新型空间方向树把多小波域中不同子带的相似系数和每个子带中各个子块的相似系数组织在一起,然后根据树的结构改进了算法中分裂排序过程。实验结果表明,SPIHT改进算法与原来的SPIHT算法相比,在相同的压缩比下可以获得更高的峰值信噪比。     

基于9-7提升小波的SPIHT编码算法

在分析SPIHT算法的基础上，针对SPIHT算法中存在的不足，采用9-7提升小波对原始图像进行小波变换，结合人眼视觉特性，对SPIHT算法的分集排序过程进行优化。实验仿真结果表明，优化的图像压缩算法是一种有效的图像压缩算法，其图像复原质量和信噪比均优于原SPIHT编码算法。     

一种新的图像压缩编码算法

对图像压缩编码算法进行了改进。首先,将小波分解后的3个高频系数进行预处理:将高频部分进行球坐标变换,降低了同一尺度内系数的相关性;基于小波域和球坐标域的两个前提,定义了多尺度模积的概念,用来控制收缩函数对小波高频部分进行收缩处理。这样,可以去除那些不影响视觉效果的小波系数以及噪声信息,达到较高的压缩比。然后,对小波变换的低频部分进行单独编码(DPCM),对球坐标下的高频部分采用改进的多级树集合分裂(SPIHT)编码。针对SPIHT编码中重复扫描的问题,引入了最大值矩阵MMP(matrix of maximum pixel),这种策略能够有效降低比较次数。仿真实验表明,本文提出的算法具有较好的编码效率。     

一种结合Contourlet和小波变换的图像编码算法

该文提出了一种Contourlet变换和小波变换相结合,使用新的空间方向树的类似SPIHT编码算法。该算法先对图像进行Contourlet变换,再对变换后的低频子带进行多级小波变换,然后根据变换后系数的结构特性,借鉴小波SPIHT编码思想,构造了一种新的空间方向树,实现了对变换后系数的类似SPIHT编码。仿真实验结果表明,该算法与小波变换,Contourlet变换和基于小波的Contourlet变换的SPIHT算法相比,重构图像保留了更多的纹理和细节信息,并且在低比特率下具有较高的峰值信噪比。     

改进的小波域三维等级树集分割视频编码方法

本文主要研究了视频图像在小波域进行压缩的三维等级树集分割编码（3D－SPIHT）方法,提出了一种改进的三维等级树集分割编码方法（13D－SPIHT）,该方法克服了3D－SPIHT的限制。通过分析和仿真实验发现,本文的改进算法在降低编码延迟的基本下基本上能达到和3D－SPIHT方法相同的编码结果,在相同的编码时延的条件下可得到更好的编码结果。     

基于3维SPIHT编码的超光谱图像压缩

提出一种针对超光谱图像压缩的3维SPIHT编码算法.通过对超光谱图像进行3维小波变换,同时去除像素数据间的空间冗余和谱间冗余.针对变换后得到的小波系数,构造一种3维空间方向树结构,并用经3维扩展后的SPIHT算法(3D SPIHT算法)对小波系数进行量化编码.实验证明,基于3维小波变换的3维SPIHT编码算法在对超光谱图像压缩时,表现出了优良的率失真性能.并且算法复杂度适中,具有嵌入式特性.     

基于最优小波包的SPIHT图像编码算法

提出了一种基于最优小波包的改进SPIHT图像编码算法.分析了各种代价函数的特点以及构建最优小波包基的算法.实验结果表明:基于最优小波包的SPIHT图像编码算法能自适应的量化小波包分解后的不同子带的系数,其峰值信噪比和重建图像质量均优于标准的SPIHT编码算法.     

基于帧间去相关的超光谱图像压缩方法

针对超光谱图像的特点和硬件实现的实际需要,提出了一种基于小波变换的前向预测帧间去相关超光谱图像压缩算法。通过图像匹配和帧间去相关,消除超光谱图像帧间的冗余,对残差图像的压缩采用基于小波变换的快速位平面结合自适应算术编码的压缩算法,按照率失真准则控制输出码流,实现了对超光谱图像的高保真压缩。通过实验证明了该方案的有效性,基于小波变换的快速位平面结合自适应算术编码的压缩算法速度优于SPIHT,而且易于硬件实现。     

ITU standardisation of very low bitrate video coding algorithms

The ITU near term standard for very low bitrate video coding, H.263 (ITU-T SG 15/1 Rapporteurs Group for Very Low Bitrate Visual Telephony, 1995), is described. Both QCIF and a sub-QCIF format (128 × 96) are mandatory picture formats for the decoder; the CIF picture format is optional. The H.263 algorithm consists of a mandatory core algorithm and four negotiable options. With H.263 a significantly better picture quality than with H.261 can be achieved, depending on the content of the video scene and the coding parameters. Also, the cost of the H.263 video codec can be kept low if only the minimum required is implemented. The negotiable options of H.263 increase the complexity of the video codec, but also significantly improve the picture quality. H.263 is part of a set of recommendations for a very low bitrate audio visual terminal that was frozen in January 1995 and is based on existing technology. A long term activity is planned by ITU for the development of a new video coding algorithm (H.263/L) with a considerable better picture quality than H.263. This standard will be developed in joint co-operation with MPEG4.     

Very low bit-rate video coding using variable block-sizeentropy-constrained residual vector quantizers

We present a practical video coding algorithm for use at very low bit rates. For efficient coding at very low bit rates, it is important to intelligently allocate bits within a frame, and so a powerful variable-rate algorithm is required. We use vector quantization to encode the motion-compensated residue signal in an H.263-like framework. For a given complexity, it is well understood that structured vector quantizers perform better than unstructured and unconstrained vector quantizers. A combination of structured vector quantizers is used in our work to encode the video sequences. The proposed codec is a multistage residual vector quantizer, with transform vector quantizers in the initial stages. The transform-VQ captures the low-frequency information, using only a small portion of the bit budget, while the later stage residual VQ captures the high-frequency information, using the remaining bits. We used a strategy to adaptively refine only areas of high activity, using recursive decomposition and selective refinement in the later stages. An entropy constraint was used to modify the codebooks to allow better entropy coding of the indexes. We evaluate the performance of the proposed codec, and compare this data with the performance of the H.263-based codec. Experimental results show that the proposed codec delivered significantly better perceptual quality along with better quantitative performance     

符合人眼视觉特征的H.263编码方案

在研究视觉阈值效应和视觉掩盖效应的基础上,提出了一个符合人眼视觉特征的失真判断准则,并将其应用到Ｈ．２６３视频编码中,以达到提高编码速度的目的。实验结果表明,这种基于人眼视觉特性的失真判断方法能在保证恢复图像主观质量和压缩效率的前提下,有效地提高编码速率。     

基于H.264的无再损帧内编码

为了在改进的H.264上实现无再损帧内编码,该文提出了一种新的基于整数线性规划的优化clip算法及改进算法,解决了H.264多次编码中由当前clip模块和帧内预测运算引入的视频畸变问题,并且改进了现有帧内预测算法的代价函数以确保多次编码时后续编码器预测值与前次编码器预测值一致。实验结果显示,与现有帧内编码算法比较,基于整数线性规划理论的帧内编码算法完全消除了现有算法导致的多次编码时的图像降质现象,在改进的H.264编解码算法中实现了严格视频无再损编码。     

Online Dictionary Learning Based Intra-frame Video Coding

In this paper, we propose an online learning based intra-frame video coding approach, exploiting the texture sparsity of natural images. The proposed method is capable of learning the basic texture elements from previous frames with convergence guaranteed, leading to effective dictionaries for sparser representation of incoming frames. Benefiting from online learning, the proposed online dictionary learning based codec (ODL codec) is able to achieve a goal that the more video frames are being coded, the less non-zero coefficients are required to be transmitted. Then, these non-zero coefficients for image patches are further quantized and coded combined with dictionary synchronization. The experimental results demonstrate that the number of non-zero coefficients of each frame decreases rapidly while more frames are encoded. Compared to the off-line mode training, the proposed ODL codec, learning from video on the fly, is able to reduce the computational complexity with fast convergence. Finally, the rate distortion performance shows improvement in terms of PSNR compared with the K-SVD dictionary based compression and H.264/AVC for intra-frame video at low bit rates.     

基于DSP的H.263码流复合

叙述一种采用DSP实现H.263标准规定的码流复合部分的方法。为了达到实时性的要求，对VLC码表的查表方法和DSP汇编程序进行了优化。所提出的码流复合优化方法已在H.263标准的硬件系统中实现。并且准备应用于MPEG－4标准的硬件系统中。     

Joint source-channel coding for motion-compensated DCT-based SNR scalable video

In this paper, we develop an approach toward joint source-channel coding for motion-compensated DCT-based scalable video coding and transmission. A framework for the optimal selection of the source and channel coding rates over all scalable layers is presented such that the overall distortion is minimized. The algorithm utilizes universal rate distortion characteristics which are obtained experimentally and show the sensitivity of the source encoder and decoder to channel errors. The proposed algorithm allocates the available bit rate between scalable layers and, within each layer, between source and channel coding. We present the results of this rate allocation algorithm for video transmission over a wireless channel using the H.263 Version 2 signal-to-noise ratio (SNR) scalable codec for source coding and rate-compatible punctured convolutional (RCPC) codes for channel coding. We discuss the performance of the algorithm with respect to the channel conditions, coding methodologies, layer rates, and number of layers.     

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.     

H．263 VIDEO CODEC IMPLEMENTATION BASED ON MULTIMEDIA DSP

This letter introduces the implementation of H.263 video codec based on multimedia DSP TM1300,and discuses several key problems related to video coding.     

Highly scalable wavelet-based video codec for very low bit-rateenvironment

We introduce a highly scalable video compression system for very low bit-rate videoconferencing and telephony applications around 10-30 kbits/s. The video codec first performs a motion-compensated three-dimensional (3-D) wavelet (packet) decomposition of a group of video frames, and then encodes the important wavelet coefficients using a new data structure called tri-zerotrees (TRI-ZTR). Together, the proposed video coding framework forms an extension of the original zero tree idea of Shapiro (1992) for still image compression. In addition, we also incorporate a high degree of video scalability into the codec by combining the layered/progressive coding strategy with the concept of embedded resolution block coding. With scalable algorithms, only one original compressed video bit stream is generated. Different subsets of the bit stream can then be selected at the decoder to support a multitude of display specifications such as bit rate, quality level, spatial resolution, frame rate, decoding hardware complexity, and end-to-end coding delay. The proposed video codec also allows precise bit rate control at both the encoder and decoder, and this can be achieved independently of the other video scaling parameters. Such a scheme is very useful for both constant and variable bit rate transmission over mobile communication channels, as well as video distribution over heterogeneous multicast networks. Finally, our simulations demonstrated comparable objective and subjective performance when compared to the ITU-T H.263 video coding standard, while providing both multirate and multiresolution video scalability