A CODING SCHEME USING GLOBAL MOTION ESTIMATION FOR AVS P-FRAME

Block matching has been used for motion estimation and motion compensation in the Audio and Video Standard （AVS） for years. While having an acceptable performance in describing motion between frames, it requires quite a few bits to represent the motion vectors. In certain circumstances, the use of global motion estimation and compensation would perform equally well or even better than the block matching in terms of motion accuracy, while it results in the coding of global motion model parameters. In this letter, we modify an AVS coder by adding （1） six global motion model parameters to the frame header, and （2） mode selection among INTRA, SKIP, INTER-16×16, INTER-16×8, INTER-8×16, INTER-8×8, and Global Motion Compensation （GMC） modes by Lagrange optimal rate-distortion criteria. Simulation results demonstrate that over 0.1dB improvement in PSNR is obtained compared to the AVS coder for an average coded P-frame with the same bitrate.     

基于运动矢量多级分析的视频全局运动估计

基于运动矢量场的视频全局运动估计相较于基于像素的估计方法具有较低的计算复杂度,因而广泛应用于视频分割及视频压缩等领域中。然而噪声和前景目标等外点区域的存在,降低了全局运动估计的准确性。为了提高全局运动估计的准确度,该文提出一种基于运动矢量多级分析的全局运动估计算法,该算法根据局部运动与全局运动的运动特性差异自适应地滤除前景目标区域,由邻域矢量间相似性度量检测出纹理平滑周期区域,最后滤除孤立的噪声区域,由滤波得到的内点区域求解全局运动参数。实验结果表明,该方法能有效地滤除外点区域,提高全局运动估计的准确性。     

Fast mode decision algorithm for intra prediction in H.264/AVC with integer transform and adaptive threshold

Compared with other existing video coding standards, H.264/AVC can achieve a significant improvement in compression performances. A robust criterion named the rate distortion optimization (RDO) is employed to select the optimal coding modes and motion vectors for each macroblock (MB), which achieves a high compression ratio while leading to a great increase in the complexity and computational load unfortunately. In this paper, a fast mode decision algorithm for H.264/AVC intra prediction based on integer transform and adaptive threshold is proposed. Before the intra prediction, integer transform operations on the original image are executed to find the directions of local textures. According to this direction, only a small part of the possible intra prediction modes are tested for RDO calculation at the first step. If the minimum mean absolute error (MMAE) of the reconstructed block corresponding to the best mode is smaller than an adaptive threshold which depends on the quantization parameter (QP), the RDO calculation is terminated. Otherwise, more possible modes need to be tested. The adaptive threshold aims to balance the compression performance and the computational load. Simulation results with various video sequences show that the fast mode decision algorithm proposed in this paper can accelerate the encoding speed significantly only with negligible PSNR loss or bit rate increment. This work is supported in part by China National Natural Science Foundation (CNSF) under Project No.60572045, the Ministry of Education of China Ph.D. Program Foundation under Project No.20050698033, and by a Cooperation Project (2005.7– 2007.7) with Microsoft Research Asia.     

Reducing the complexity of MPEG-4 global motion estimation using pixel subsampling

MPEG-4 uses a perspective model for global motion estimation. The region of support for global motion representation consists of the entire image frame. Estimating global motion parameters is very expensive computationally, since all the pixels in the frames are involved in the computation. Therefore, computationally efficient global motion estimation techniques are sought-after. It is shown that real-time global motion estimation in an MPEG-4 video codec can be achieved by using a pixel subsampling method based on regular subsampling patterns. Simulation results demonstrated that the proposed method was capable of speeding up the conventional all- pixel GME approach by more than 11 times, with a subsampling ratio of 1/16, without significant loss in estimation accuracy and compression efficiency.     

基于运动矢量场的运动目标区域检测

基于稀疏运动矢量场,提出一种动态背景下的运动 目标区域检测方法。根据运动矢量场特性分析进行全局运动 参数估计和全局运动补偿,实现动态场景中的背景校正;利用最大树数据结构, 基于运动矢量补偿误差分级表示视频帧中 运动基本一致的连通区域,进行运动区域初始分类;根据运动目标在空间上的连通性和运动 一致性的特点,选择区域相似性 度量准则,进行区域合并和滤波,将具有相似运动的连通区域合并,实现运动目标区域检测 。将检测出的运动目标区域作为 运动矢量外点反过来又应用于全局运动参数估计过程中,全局运动估计和运动目标区域检测 交替地进行,不仅加快了它们的 计算速度,同时也提高了它们计算和检测的准确性。实验结果表明,本文算法能较好地补偿 序列的全局运动,有效地检测出 局部目标运动区域。     

一种高效的基于H.264/AVC压缩域信息的全局运动估计方法

本文提出了一种基于H.264/AVC压缩域的高效全局运动估计算法.由于H.264采用了多种新的视频压缩编码技术,使得其压缩码流的运动矢量(MV)场中包含大量噪声运动矢量,可参与全局运动估计的运动矢量相对较少.噪声运动矢量这里指的是与全局运动不相符的运动矢量.为了降低噪声运动矢量的影响、提高全局运动估计的精度和效率,在全...     

Double compression detection based on local motion vector field analysis in static-background videos

Videos captured by stationary cameras are widely used in video surveillance and video conference. This kind of video often has static or gradually changed background. By analyzing the properties of static-background videos, this work presents a novel approach to detect double MPEG-4 compression based on local motion vector field analysis in static-background videos. For a given suspicious video, the local motion vector field is used to segment background regions in each frame. According to the segmentation of backgrounds and the motion strength of foregrounds, the modified prediction residual sequence is calculated, which retains robust fingerprints of double compression. After post-processing, the detection and GOP estimation results are obtained by applying the temporal periodic analysis method to the final feature sequence. Experimental results have demonstrated better robustness and efficiency of the proposed method in comparison to several state-of-the-art methods. Besides, the proposed method is more robust to various rate control modes.     

Improved nonlinear multiuser precoding using lattice reduction

Recent theoretical results show that multiuser techniques such as Spatial Division Multiple Access can significantly improve system capacity. In order to achieve this end, lots of precoding methods have been proposed, among which Vector Perturbation precoding has the best Symbol Error Rate performance but with the hugest complexity in searching for the optimal perturbation vector. In this paper, we propose a low complexity, near optimal multiuser precoding method by utilizing lattice reduction of the channel matrix. The perturbation vector is composed of an integer part and a non-integer part, which are designed to simultaneously improve power efficiency and minimize the mean squared error MSE. The integer perturbation vector is calculated implicitly with modulo operation, and the non-integer perturbation can be solved in closed form under MSE minimization criterion. Simulation results demonstrate the effectiveness of the proposed methods. This work was supported by National Basic Research Program of China (2007CB310603), National Natural Science Foundation of China (60496310, 60672093), High Technology Project of China (2007AA01Z262) and Huawei Foudation.     

Robust global motion estimation oriented to video object segmentation.

Most global motion estimation (GME) methods are oriented to video coding while video object segmentation methods either assume no global motion (GM) or directly adopt a coding-oriented method to compensate for GM. This paper proposes a hierarchical differential GME method oriented to video object segmentation. A scheme which combines three-step search and motion parameters prediction is proposed for initial estimation to increase efficiency. A robust estimator that uses object information to reject outliers introduced by local motion is also proposed. For the first frame, when the object information is unavailable, a robust estimator is proposed which rejects outliers by examining their distribution in local neighborhoods of the error between the current and the motion-compensated previous frame. Subjective and objective results show that the proposed method is more robust, more oriented to video object segmentation, and faster than the referenced methods.     

Fast motion estimation for surveillance video compression

In this article, novel approaches to perform efficient motion estimation specific to surveillance video compression are proposed. These includes (i) selective (ii) tracker-based and (iii) multi-frame-based motion estimation. In selective approach, motion vector search is performed for only those frames that contain some motion activity. In another approach, contrary to performing motion estimation on the encoder side, motion vectors are calculated using information of a surveillance video tracker. This approach is quicker but for some scenarios it degrades the visual perception of the video compared with selective approach. In an effort to speed up multi-frame motion estimation, we propose a fast multiple reference frames-based motion estimation technique for surveillance videos. Experimental evaluation shows that significant reduction in computational complexity can be achieved by applying the proposed strategies.     

Model-based quarter-pixel motion estimation with low computational complexity

Proposed is an interpolation-free quarter-pixel motion estimation method based on a mathematical model for video encoding. In this method, only three shift operators and four compare operators are required in each horizontal and vertical direction to find a quarter-pixel resolution motion vector. Experimental results show that the proposed method reaches almost the same performance as an interpolation-based full-search for quarter-pixel motion estimation with much less computational complexity.     

A Robust hierarchical motion estimation algorithm in noisy image sequences in the bispectrum domain

The present study describes a robust hierarchical motion estimation algorithm in noisy image sequences using the bispectrum. The motion can be characterized by an affine model and the parameters of an affine motion model are estimated by means third-order auto-bispectrum and cross-bispectrum measures. The basic components of this framework to obtain motion vectors are (i) pyramid construction, (ii) motion estimation and (iii) coarse-to-fine refinement. The entire motion is decomposed as a global and a local motion field, which helps accurately obtain high resolution estimates for the local motion field. Simulation results are presented and compared to those obtained from the phase correlation algorithm. The results demonstrate that the proposed method is more suited than the phase correlation algorithm to analyses complex noisy image sequences. On the other hand, our method produces smoother displacement vector field with a more accurate measure of object motion in different signal-to-noise ratio scenarios.     

一种新的视频编码的块运动估计算法

本文提出了一种连续判别的非线性预测搜索ＮＰＳＳＤ块运动估计算法,可以用于视频压缩的一些国际标准,如Ｈ．２６１,Ｈ．２６３,ＭＰＥＧ１,ＭＰＥＧ２,ＨＤＴＶ中。ＮＰＳＳＤ算法充分利用了序列图像的实际运动矢量与预测矢量之间的位移的空间分布特性－－中心偏置分布特性和时间上的相关特性,并在搜索过程中采用了中止判别和搜索判别,可以明显地减少运动搜索复杂度。仿真表明这种算法减少了搜索次数,提高了搜索效率,降低     

A new hypersphere support vector machine algorithm

The hypersphere support vector machine is a new algorithm in pattern recognition. By studying three kinds ofhypersphere support vector machines, it is found that their solutions are identical and the margin between two classes of samples is zero or is not unique. In this letter, a new kind ofhypersphere support vector machine is proposed. By introducing a parameter n（n〉1）, a unique solution of the margin can be obtained.Theoretical analysis and experimental results show that the proposed algorithm can achieve better generalization performance.     

Low complexity motion estimation utilising spatial correlation

An efficient algorithm is proposed to reduce the computational complexity of block matching motion estimation by using the characteristics of spatial correlation. The proposed algorithm is to skip the motion vector search of inside macroblocks surrounded by identical motion vectors. Experimental results show that the proposed algorithm reduces computational complexity by 52.5% compared to conventional motion estimation at the cost of negligible performance degradation.     

Improvement of motion estimation accuracy using gradient vectordistribution in advanced picture coding

This paper describes methods of improving the accuracy of a gradient-based motion estimation method that uses an eigenvalue algorithm. First, we propose reliability indexes of the estimated motion vector. Next, we classify the motion images by the proposed indexes into categories and analyze the characteristics of each classified image. According to the categories of the image characteristics, we use different methods in order to improve the accuracy of each motion estimation. Simulation results show that these proposed methods are effective in improving the motion estimation accuracy     

一种基于硬件实现的快速运动估计半像素级搜索算法

研究了在绝对差和准则下的整像素级块匹配和半像素级块匹配的联系，对绝对差和进行了合理的数学曲线拟合，通过数学曲线来预测最小绝对差和所在半像素位置，从而得到半像素级最佳匹配矢量。分析了三种不同的凹函数预测模型，提出了一种适合硬件实现的运动估计快速半像素级搜索算法。该算法直接根据整像素级运动估计的结果来推算半像素级运动估计结果，在很大程度上降低了半像素级运动估计的运算复杂度，从而利用低码率视频编码的实时实现。试验结果表明该算法可获得较好的重建图像质量。该算法利于硬件实现，可以方便地集成到现有的视频编码器中，具有较好的实用价值。     

Refinement method for structure from stereo motion

A new method for overcoming bas-relief ambiguity, using a calibrated stereo image sequence, is presented. The proposed method uses a direct method for motion estimation as the initial guess, and refines both stereo and motion displacement with sub-pixel accuracy. Experimental results show that the proposed algorithm improves the estimation accuracy under such ambiguity     

A variable block size motion estimation algorithm for real-time H.264 video encoding

This paper presents an efficient variable block size motion estimation algorithm for use in real-time H.264 video encoder implementation. In this recursive motion estimation algorithm, results of variable block size modes and motion vectors previously obtained for neighboring macroblocks are used in determining the best mode and motion vectors for encoding the current macroblock. Considering only a limited number of well chosen candidates helps reduce the computational complexity drastically. An additional fine search stage to refine the initially selected motion vector enhances the motion estimator accuracy and SNR performance to a value close to that of full search algorithm. The proposed methods result in over 80% reduction in the encoding time over full search reference implementation and around 55% improvement in the encoding time over the fast motion estimation algorithm (FME) of the reference implementation. The average SNR and compression performance do not show significant difference from the reference implementation. Results based on a number of video sequences are presented to demonstrate the advantage of using the proposed motion estimation technique.     

基于头肩图像中脸部轮廓的运动估值

对于可视电话中的头肩图像,在提取出脸部轮廓后,在脸部区通过搜索出全局的二维运动参数来确定各像块运动矢量的初始搜索点。在此基础上搜索精确的运动矢量时,搜索范围很小,搜索结果更符合真实运动,保证了运动矢量场的一致性。因此,既加快了运动估值的速度,又节省了编码运动矢量所用的比特数,使图像的质量有所提高。