基于MPEG-4的运动估计算法及硬件实现设计

提出的运动估计算法在块运动向量搜索中采用菱形搜索替代传统全搜索策略,在保证编码精度的条件下,减少了50%的搜索像素点,加快了编码速度.设计的运动估计硬件加速器方案正是采用这种搜索算法.仿真实验采用在标准的MPEG-4验证软件中植入硬件加速器模块的方法.其结果显示改进的4MV搜索策略在图像的PSNR和每帧图像的平均比特数方面与全搜索策略相当.这种新型的运动估计算法对设计运动估计硬件加速器有着重要的指导意义.     

Motion estimation based on multiple local constraints and nonlinear smoothing

A new algorithm for estimating motion from image sequences is presented. Initial motion estimates are determined based on a least-squares solution to a set of independent linear constraints on the motion at a pixel. These initial estimates are then improved by a nonlinear smoothing operation. The results of this algorithm are compared with those obtained by the Horn-Schunck algorithm on a number of image sequences.     

基于MPEG-4的高效屏幕编/解码器的设计与实现

随着计算机和通信技术的发展,屏幕共享技术越来越得到人们的重视。特别是在视频会议和远程教育这样的应用中,屏幕数据作为一个必不可少的“源”,其重要性已经超过了视频数据。屏幕共享技术中最核心的问题就是对屏幕数据的编码,该文根据屏幕数据的特点,借鉴了MPEG-4的思想,设计并实现了一个高效的屏幕编／解码器。     

New results using an integrated model and recursive algorithm for image motion estimation

A linear equation in the affine parameters used to model image motion may be derived by Taylor series expansion and truncation, and windowed spatial integration. Two methods for reducing errors in the Taylor approximation are discussed and results are presented.     

An estimation problem in compact Lie groups

In this paper an estimation problem is formulated and solved where the process evolves in a compact, semisimple Lie group. The problem is to find explicitly the conditional probability density of a random initial condition of a Brownian motion in the Lie group given a vector-valued function of the group-valued Brownian motion at some fixed positive time. This function is constant on orbits of the Lie group formed by conjugation. The conditional probability density function has a simple, explicit form using some orbit properties of the Lie group. Many physical problems can be modelled as evolving on compact, semisimple Lie groups, e.g. the motion of a rigid body with a fixed point.     

数字图像稳像算法研究

介绍了数字图像稳像算法的整个流程,包括三部分:运动估计、运动决定和运动补偿.重点介绍了运动估计算法和运动补偿中的滤波算法;详细阐述了几种最基本的运动估计算法,其它的运动估计算法可以通过这些基本算法延伸发展得到;列出了三种常用的滤波算法:中值滤波、kalman滤波和二次B样条曲线法,应用于不同的场合;提出了两种方法:裁减和拼接,用来解决当前帧补偿后出现的空白区域问题.最后,展示了一种基于投影估计和kalman滤波的稳像算法的试验结果.通过这些方法的介绍,可以对稳像算法有更直观的了解,探讨了进一步研究的重点.     

Automatic estimation of asymmetry for gradient-based alignment of noisy images on Lie group

Many parametric image alignment approaches assume equality of the images to register up to motion compensation. In presence of noise this assumption does not hold. In particular, for gradient-based approaches, which rely on the optimization of an error functional with gradient descent methods, the performances depend on the amount of noise in each image. We propose in this paper to use the Asymmetric Composition on Lie groups (ACL) formulation of the alignment problem to improve the robustness in presence of asymmetric levels of noise. The ACL formulation, generalizing state-of-the-art gradient-based image alignment, introduces a parameter to weight the influence of the images during the optimization. Three new methods are presented to estimate this asymmetry parameter: one supervised (MVACL) and two fully automatic (AACL and GACL). Theoretical results and experimental validation show how the new algorithms improve robustness in presence of noise. Finally, we illustrate the interest of the new approaches for object tracking under low-light conditions.     

Theorems on the structure of finite dimensional estimation algebras

In this paper we proved several theorems concerning the structure of finite dimensional estimation algebras. In particular, under proper technical assumptions, we proved the following: (1) The observation of a filtering system must be linear if the estimation algebra is finite dimensional. (2) All elements of a finite dimensional estimation algebra belong to a special class of polynomial differential operators. (3) All finite dimensional estimation algebras are solvable.     

极低码率视频编码中块自适应分割运动估值

在极低码率视频编码运动估值过程中，针对视频对象的边缘形状特征，将宏块按不同形状的模板自适应地进行分割，同时引入近期、远期２个参考帧进行块匹配。为提高搜索速度，首先判断出不需编码的宏块，并引用了一种快速搜索算法。实验结果表明，与Ｈ．２６３先进预测模式相比，采用所建议的运动补偿方法，图象的信嗓比得到明显的提高。     

Efficient edge-based object tracking

Object tracking has been widely applied to video surveillance, robot localization and human-computer interaction. In this paper, an edge-based tracking algorithm is proposed. We extract the feature points by efficiently utilizing the image edges in the object region. Then the parameter vector of the object's motion model is estimated based on minimizing the sum-of-squared differences between the reference feature points in the reference frame and the observed feature points in the tracking sequence frame. The experiments show that the edge-based tracking algorithm proposed by us can track object efficiently under uniform and varying illumination conditions.     

基于DCT域的MPEG-4编码器改进方法研究

在对MPEG-4标准的分析和研究的基础上,对MPEG-4编码器提出了一种基于离散余弦变换(DCT)域运动估计的改进方案。这种编码结构直接在DCT变换域中进行运动估计,不需要将DCT系数变换回空间域。因此它能有效地减少编码的运算次数和编码结构的复杂度,满足实时编码的要求。     

Optical flow estimation for motion-compensated compression

The computation of optical flow within an image sequence is one of the most widely used techniques in computer vision. In this paper, we present a new approach to estimate the velocity field for motion-compensated compression. It is derived by a nonlinear system using the direct temporal integral of the brightness conservation constraint equation or the Displaced Frame Difference (DFD) equation. To solve the nonlinear system of equations, an adaptive framework is used, which employs velocity field modeling, a nonlinear least-squares model, Gauss–Newton and Levenberg–Marquardt techniques, and an algorithm of the progressive relaxation of the over-constraint. The three criteria by which successful motion-compensated compression is judged are 1.) The fidelity with which the estimated optical flow matches the ground truth motion, 2.) The relative absence of artifacts and “dirty window” effects for frame interpolation, and 3.) The cost to code the motion vector field. We base our estimated flow field on a single minimized target function, which leads to motion-compensated predictions without incurring penalties in any of these three criteria. In particular, we compare our proposed algorithm results with those from Block-Matching Algorithms (BMA), and show that with nearly the same number of displacement vectors per fixed block size, the performance of our algorithm exceeds that of BMA in all the three above points. We also test the algorithm on synthetic and natural image sequences, and use it to demonstrate applications for motion-compensated compression.     

Efficient normal estimation using variable‐size operator

Shading an object is to simulate the behaviour of light incident on its surfaces. It is necessary to calculate normal vectors on the surfaces of the object for shading it. Since objects do not contain surface inclination in voxel‐based representation, a normal vector for each voxel must be estimated from the relative position of its neighbouring voxels that have the same data value. The previously devised methods that use fixed‐size gradient operators can estimate normal vectors accurately only in a limited area and may cause some errors and artefacts. In this paper we propose an efficient normal estimation method using an extended central difference operator whose size can vary according to the arrangement of surface‐comprising voxels. This method calculates normals more accurately than the previous methods and its computation time is shorter than that of methods that guarantee the same image quality. In order to show the improvement, we compare the quality of resulting images and processing time by implementing the newly proposed method and the previous methods and then applying them to some volume data. Copyright © 1999 John Wiley & Sons, Ltd.     

一种适用于MPEG-4形状编码的快速运动估计算法

运动估计是MPEG-4形状编码的一项关键技术,本文提出了一种适用于形状编码的快速运动估计算法。算法首先在参考帧中进行扫描,得出视频对象的二值边界掩模;在匹配运算时使用lbit的异或运算代替原有的加法运算;设定有效的中止准则,对于静止点直接中止搜索;在搜索过程中采用了渐进消除算法,能够在不影响搜索精度的前提下减少搜索点。实验结果表明使用本文的快速搜索算法,运动估计中的运算量比MPEG-4 VM原有搜索算法有较大幅度的降低,且编码后的码字长度与原算法基本一致。     

Parametric ego-motion estimation for vehicle surround analysis using an omnidirectional camera

Omnidirectional cameras that give a 360° panoramic view of the surroundings have recently been used in many applications such as robotics, navigation, and surveillance. This paper describes the application of parametric ego-motion estimation for vehicle detection to perform surround analysis using an automobile-mounted camera. For this purpose, the parametric planar motion model is integrated with the transformations to compensate distortion in omnidirectional images. The framework is used to detect objects with independent motion or height above the road. Camera calibration as well as the approximate vehicle speed obtained from a CAN bus are integrated with the motion information from spatial and temporal gradients using a Bayesian approach. The approach is tested for various configurations of an automobile-mounted omni camera as well as a rectilinear camera. Successful detection and tracking of moving vehicles and generation of a surround map are demonstrated for application to intelligent driver support.Received: 1 August 2003, Accepted: 8 July 2004, Published online: 3 February 2005     

Face segmentation and tracking based on connected operators and partition projection

A new technique for segmenting and tracking human faces in video sequences is presented. The algorithm relies on the concepts of connected operators and partition projection to tackle the problems of face segmentation and tracking, respectively. It uses a connected operator to extract the connected component that more likely belongs to a face. Such a connected operator is implemented by means of a Binary Partition Tree. A set of connected regions (a node in the tree) is selected maximizing the estimation of the likelihood of being part of a face. This way, a first estimate of the face is obtained. Final face segmentation is carried out by a face extraction step that applies the previous maximization in the partition space. Faces are tracked through the sequence based on the partition projection approach. Partition projection accommodates the partition of the previous image into the information of the current frame. The current image is classified into face, no face and uncertain regions by projecting the previous face partition. Therefore, the projection yields the first estimate of the face. The face core component is grown up to obtain the final face segmentation using the previous face extraction process. The technique has been successfully assessed using several test sequences in raw format (MPEG-4 database) as well as in MPEG-1 format (from the MPEG-7 database).     

Mean estimation over numeric data with personalized local differential privacy

The fast development of the Internet and mobile devices results in a crowdsensing business model, where individuals (users) are willing to contribute their data to help the institution (data collector) analyze and release useful information. However, the reveal of personal data will bring huge privacy threats to users, which will impede the wide application of the crowdsensing model. To settle the problem, the definition of local differential privacy (LDP) is proposed. Afterwards, to respond to the varied privacy preference of users, researchers propose a new model, i.e., personalized local differential privacy (PLDP), which allow users to specify their own privacy parameters. In this paper, we focus on a basic task of calculating the mean value over a single numeric attribute with PLDP. Based on the previous schemes for mean estimation under LDP, we employ PLDP model to design novel schemes (LAP, DCP, PWP) to provide personalized privacy for each user. We then theoretically analysis the worst-case variance of three proposed schemes and conduct experiments on synthetic and real datasets to evaluate the performance of three methods. The theoretical and experimental results show the optimality of PWP in the low privacy regime and a slight advantage of DCP in the high privacy regime.     

Parametrizing Del Pezzo surfaces of degree 8 using Lie algebras

For a Del Pezzo surface of degree 8 given over the rationals we decide whether there is a rational parametrization of the surface and construct one in the affirmative case. We define and use the Lie algebra of the surface to reach the aim.     

一种有效的视频信号编码块效应消减技术

针对视频信号编码中存在的块效应，提出了一个能有效提高解码图象质量的编码方案。首先，给出一种按系数自适应ＤＣＴ编码算法的新的逻辑实现结构；然后，用一种简单而有效的自适应控制策略来代替极其复杂费时的严格的自适应方法。同时，为了克服低比特率下粗糙量化导致自适应性能下降的缺点，设计了一种具有良好性能的运动估计快速算法用来提高适应能力。实验结果表明，与常规的基于ＤＣＴ的编码方法相比，这种编码方案性能有显著的提高。     

基于统计学理论的参数模型运动估计方法

运动估计对视频编码十分重要,基于参数模型的运动估计方法也越来越受到人们的关注,参数模型的选择是该方法的关键。基于此,提出了基于统计学原理的模型选择方法,它以少量的图像数据流为基础,通过参数估计,并分析各近似模型的预测风险和误差,选出最优模型,它最符合预测对象的实际发展变化规律,进而利用该模型对未知对象进行运动估计。试验结果表明,在对实际图像序列进行运动估计时,这种方法是可靠并且实用的。