基于帧间差的区域光流分析及其应用

传统视频运动检测常用帧间差、背景差等方法检测图像变化的存在,它们能敏感地给出变化区域,在此基础上可方便提取运动对象的位置和轮廓等静态特性,但并不能直接得到运动对象的速度、方向等运动特性;光流法虽可进一步给出运动场中每个像素位置的运动特性,但它所涉及的计算量庞大,难以直接应用于有实时需求的场合。因此,文章提出了一种基于联合帧间差的区域光流分析方法,通过联合帧间差方法提取运动区域,针对运动区域进行光流计算,保持了实时处理所需的速度并降低了光流计算的计算代价,并讨论了其在视频监控、交通监管等场合的应用。     

Moving object detection using region tracking

For many vision-based systems, it is important to detect a moving object automatically. The region-based motion estimation method is popular for automatic moving object detection. The region-based method has several advantages in that it is robust to noise and variations in illumination. However, there is a critical problem in that there exists an occlusion problem which is caused by the movement of the object. The occlusion problem results in an incorrect motion estimation and faulty detection of moving objects. When there are occlusion regions, the motion vector is not correctly estimated. That is, a stationary background in the occluded region can be classified as a moving object.In order to overcome this occlusion problem, a new occlusion detection algorithm is proposed. The proposed occlusion detection algorithm is motivated by the assumption that the distribution of the error histogram of the occlusion region is different from that of the nonocclusion region. The proposed algorithm uses the mean and variance values to decide whether an occlusion has occurred in the region. Therefore, the proposed occlusion detection and motion estimation scheme detects the moving regions and estimates the new motion vector, while avoiding misdetection caused by the occlusion problem. The experimental results for several video sequences demonstrate the robustness of the proposed approach to the occlusion problem.This work was presented in part at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

一种基于自适应梯度的运动估计算法

给出了一种基于Horn-Schunck的改进光流估计算法，计算了当前帧的前向梯度、后向梯度，根据代价函数自适应地选择前向梯度与后向梯度，减小光流估计时的遮挡问题。试验表明该算法是有效的。     

Three-dimensional scene flow

Just as optical flow is the two-dimensional motion of points in an image, scene flow is the three-dimensional motion of points in the world. The fundamental difficulty with optical flow is that only the normal flow can be computed directly from the image measurements, without some form of smoothing or regularization. In this paper, we begin by showing that the same fundamental limitation applies to scene flow; however, many cameras are used to image the scene. There are then two choices when computing scene flow: 1) perform the regularization in the images or 2) perform the regularization on the surface of the object in the scene. In this paper, we choose to compute scene flow using regularization in the images. We describe three algorithms, the first two for computing scene flow from optical flows and the third for constraining scene structure from the inconsistencies in multiple optical flows.     

适用于遮挡问题的目标跟踪算法

提出一种基于网格模型的目标跟踪算法．该算法首先进行遮挡区域检测，然后进行网格结点的运动估计和网格更新过程完成目标的多帧跟踪．改进的遮挡区域检测算法有效地提高了检测准确度，从而确保遮挡区域的准确跟踪；网格结点的运动估计是通过特征窗口运动补偿匹配完成，可以有效地克服块效应．实验证明，该算法解决了二维运动估计时网格模型在遮挡区域存在的问题，并可以有效地进行目标准确跟踪．     

Multimodal estimation of discontinuous optical flow using Markovrandom fields

The estimation of dense velocity fields from image sequences is basically an ill-posed problem, primarily because the data only partially constrain the solution. It is rendered especially difficult by the presence of motion boundaries and occlusion regions which are not taken into account by standard regularization approaches. In this paper, the authors present a multimodal approach to the problem of motion estimation in which the computation of visual motion is based on several complementary constraints. It is shown that multiple constraints can provide more accurate flow estimation in a wide range of circumstances. The theoretical framework relies on Bayesian estimation associated with global statistical models, namely, Markov random fields. The constraints introduced here aim to address the following issues: optical flow estimation while preserving motion boundaries, processing of occlusion regions, fusion between gradient and feature-based motion constraint equations. Deterministic relaxation algorithms are used to merge information and to provide a solution to the maximum a posteriori estimation of the unknown dense motion field. The algorithm is well suited to a multiresolution implementation which brings an appreciable speed-up as well as a significant improvement of estimation when large displacements are present in the scene. Experiments on synthetic and real world image sequences are reported     

基于遮挡区域建模和目标运动估计的动态遮挡规避方法

对于运动视觉目标，如何对遮挡区域进行规避是视觉领域一个具有挑战性的问题.本文提出了一种新颖的基于运动视觉目标深度图像利用遮挡信息实现动态遮挡规避的方法.该方法主要利用遮挡区域最佳观测方位模型和视觉目标运动估计方程，通过合理规划摄像机的观测方位逐渐完成对遮挡区域的观测.主要贡献在于:1）提出了深度图像遮挡边界中关键点的概念，利用其构建关键线段对遮挡区域进行快速建模；2）基于关键线段和遮挡区域建模结果，提出了一种构建遮挡区域最佳观测方位模型的方法；3）提出一种混合曲率特征，通过计算深度图像对应的混合曲率矩阵，增加了图像匹配过程中提取特征点的数量，有利于准确估计视觉目标的运动.实验结果验证了所提方法的可行性和有效性.     

协同运动状态估计的多目标跟踪算法

多目标跟踪在视频分析场景中有着广泛的应用,如人机交互、虚拟现实、自动驾驶、视频监控和机器人导航等。多目标跟踪问题可以表示为在已有的检测数据上进行目标轨迹关联,检测算法的准确性对跟踪性能起着关键性的作用。在基于检测的目标跟踪框架中,提出了一种协同运动状态估计的跟踪算法,该算法主要关注相邻帧之间的数据关联,从目标检测、目标运动状态估计和数据关联这3个方面来直接解决多目标跟踪面临的挑战。首先,对于目标检测,采用Multi Scale Convolutional Neural Network(MS-CNN)算法作为检测器,这是因为深度学习在检测的效益上优于传统的机器学习方法;其次,为了更好地预测目标的运动状态和处理目标间的遮挡,针对不同状态的目标采取不同的运动估计方法: 采用核相关滤波来评估处于跟踪状态的目标的运动状态,当目标处于遮挡状态时,采用卡尔曼滤波做运动估计;最后,采用Kuhn-Munkres算法对检测目标和跟踪轨迹做数据关联。通过大量的实验证实了算法的有效性,且实验结果表明算法的准确性很高。     

Image flow segmentation and estimation by constraint lineclustering

Image flow is the velocity field in the image plane caused by the motion of the observer, objects in the scene, or apparent motion, and can contain discontinuities due to object occlusion in the scene. An algorithm that can estimate the image flow velocity field when there are discontinuities due to occlusions is described. The constraint line clustering algorithm uses a statistical test to estimate the image flow velocity field in the presence of step discontinuities in the image irradiance or velocity field. Particular emphasis is placed on motion estimation and segmentation in situations such as random dot patterns where motion is the only cue to segmentation. Experimental results on a demanding synthetic test case and a real image are presented. A smoothing algorithm for improving the velocity field estimate is also described. The smoothing algorithm constructs a smooth estimate of the velocity field by approximating a surface between step discontinuities. It is noted that the velocity field estimate can be improved using surface reconstruction between velocity field boundaries     

Robust tracking with adaptive appearance learning and occlusion detection

It is still challenging to design a robust and efficient tracking algorithm in complex scenes. We propose a new object tracking algorithm with adaptive appearance learning and occlusion detection in an efficient self-tuning particle filter framework. The appearance of an object is modeled with a set of weighted and ordered submanifolds, which can guarantee the adaptability when there is fast illumination or pose change. To overcome the occlusion problem, we use the reconstruction error data of the appearance model to extract occlusion region by graph cuts. And the tracking result is improved with feedback of occlusion detection. The motion model is also integrated with adaptability to overcome the abrupt motion problem. To improve the efficiency of particle filter, the number of samples is tuned with respect to the scene conditions. Experimental results demonstrate that our algorithm can achieve great robustness, high accuracy and good efficiency in challenging scenes.     

基于部件的对象实时跟踪

针对视频序列中出现的遮挡等问题,提出了一种基于部件的对象跟踪方法。该方法将目标中的多个部件作为跟踪对象,采用基于核的灰度直方图来描述跟踪对象中的各个部件,通过卡尔曼滤波器预测部件的参数,继而利用直方图进行修正,以完成跟踪。实验证明,基于部件的跟踪方法不但能够有效地克服遮挡问题,而且能克服对象内部存在的相对运动以及非刚体变形等问题,具有良好的实时性和很好的跟踪效果。     

Tracking and Motion Estimation of the Articulated Object: a Hierarchical Kalman Filter Approach

Real-time motion capture plays a very important role in various applications, such as 3D interface for virtual reality systems, digital puppetry, and real-time character animation. In this paper we challenge the problem of estimating and recognizing the motion of articulated objects using theoptical motion capturetechnique. In addition, we present an effective method to control the articulated human figure in realtime.The heart of this problem is the estimation of 3D motion and posture of an articulated, volumetric object using feature points from a sequence of multiple perspective views. Under some moderate assumptions such as smooth motion and known initial posture, we develop a model-based technique for the recovery of the 3D location and motion of a rigid object using a variation of Kalman filter. The posture of the 3D volumatric model is updated by the 2D image flow of the feature points for all views. Two novel concepts – the hierarchical Kalman filter (KHF) and the adaptive hierarchical structure (AHS) incorporating the kinematic properties of the articulated object – are proposed to extend our formulation for the rigid object to the articulated one. Our formulation also allows us to avoid two classic problems in 3D tracking: the multi-view correspondence problem, and the occlusion problem. By adding more cameras and placing them appropriately, our approach can deal with the motion of the object in a very wide area. Furthermore, multiple objects can be handled by managing multiple AHSs and processing multiple HKFs.We show the validity of our approach using the synthetic data acquired simultaneously from the multiple virtual camera in a virtual environment (VE) and real data derived from a moving light display with walking motion. The results confirm that the model-based algorithm works well on the tracking of multiple rigid objects.     

Attention-from-motion: A factorization approach for detecting attention objects in motion

This paper introduces the notion of attention-from-motion in which the objective is to identify, from an image sequence, only those object in motions that capture visual attention (VA). Following the important concept in film production, viz, the tracking shot, we define the attention object in motion (AOM) as those that are tracked by the camera. Three components are proposed to form an attention-from-motion framework: (i) a new factorization form of the measurement matrix to describe dynamic geometry of moving object observed by moving camera; (ii) determination of single AOM based on the analysis of certain structure on the motion matrix; (iii) an iterative framework for detecting multiple AOMs. The proposed analysis of structure from factorization enables the detection of AOMs even when only partial data is available due to occlusion and over-segmentation. Without recovering the motion of either object or camera, the proposed method can detect AOM robustly from any combination of camera motion and object motion and even for degenerate motion.     

全局多极团的分层关联多目标跟踪

目的 由于背景的复杂性,光照的多变性以及目标的相关性等因素的影响,使得多目标跟踪算法的鲁棒性相对较差。目前,在多目标跟踪问题中面临的主要挑战包括：遮挡、误检、目标运动的复杂性以及由于目标具有相似的外观特征所引起的模糊性。针对以上问题,提出一种基于全局多极团的分层关联多目标跟踪算法。方法 该方法以数据关联中的全局关联为依托,基于分层和网络流思想,跟踪采用两层框架,每一层中均利用较短的轨迹片段形成更长的轨迹,根据网络流思想,首先构建网络的无向图,其中无向图的结点是由几个轨迹片段构成的,无向图权值的确定是利用目标的运动模型和外观模型的线性组合得到,然后借助聚合虚拟结点处理目标之间的遮挡问题,接着重点加入空间约束以解决身份转换的问题。最后利用最大二值整数规划在叠加片段上求解无向图,同时得到多个极大团。结果 实验在公共数据集上进行,通过在TUD-Stadmitte、TUD-Crossing、PETS2009、Parking Lot 1、Parking Lot 2、Town Center这6个数据集上验证,该方法对各个数据集跟踪准确度均有提高,其中针对数据集TUD-Stadmitte提高了5%以上,针对数据集Town Center处理的身份转换数量减少了12个。结论 本文依据数据关联思想,提出一种全局多极团的分层关联多目标跟踪算法,其中重点加入的空间约束能有效地处理多目标跟踪问题,尤其涉及遮挡问题,效果更佳。在智能视频监控领域中该方法具有实际应用价值。     

双光流网络指导的视频目标检测

目的 卷积神经网络广泛应用于目标检测中,视频目标检测的任务是在序列图像中对运动目标进行分类和定位。现有的大部分视频目标检测方法在静态图像目标检测器的基础上,利用视频特有的时间相关性来解决运动目标遮挡、模糊等现象导致的漏检和误检问题。方法 本文提出一种双光流网络指导的视频目标检测模型,在两阶段目标检测的框架下,对于不同间距的近邻帧,利用两种不同的光流网络估计光流场进行多帧图像特征融合,对于与当前帧间距较小的近邻帧,利用小位移运动估计的光流网络估计光流场,对于间距较大的近邻帧,利用大位移运动估计的光流网络估计光流场,并在光流的指导下融合多个近邻帧的特征来补偿当前帧的特征。结果 实验结果表明,本文模型的mAP（mean average precision）为76.4%,相比于TCN（temporal convolutional networks）模型、TPN+LSTM（tubelet proposal network and long short term memory network）模型、D（&T loss）模型和FGFA（flow-guided feature aggregation）模型分别提高了28.9%、8.0%、0.6%和0.2%。结论 本文模型利用视频特有的时间相关性,通过双光流网络能够准确地从近邻帧补偿当前帧的特征,提高了视频目标检测的准确率,较好地解决了视频目标检测中目标漏检和误检的问题。     

融合HOG与ARMA模型的粒子滤波跟踪

传统的粒子滤波算法在跟踪目标受到相似背景干扰和遮挡或跟踪目标高速运动时,容易造成跟踪误差增大或跟踪失效的影响。针对室外运动目标跟踪的复杂性,提出一种对于干扰适应性较强的融合梯度方向直方图与自回归移动平均(ARMA)模型的粒子滤波跟踪方法。建立ARMA运动模型,用前两帧目标的位姿状态预测目标下一帧的状态,解决目标跟踪的角度变化与部分遮挡问题。实验结果表明,该模型能克服光照突变引发目标色彩突变的问题。     

Dynamic occlusion analysis in optical flow fields

Optical flow can be used to locate dynamic occlusion boundaries in an image sequence. We derive an edge detection algorithm sensitive to changes in flow fields likely to be associated with occlusion. The algorithm is patterned after the Marr-Hildreth zero-crossing detectors currently used to locate boundaries in scalar fields. Zero-crossing detectors are extended to identify changes in direction and/or magnitude in a vector-valued flow field. As a result, the detector works for flow boundaries generated due to the relative motion of two overlapping surfaces, as well as the simpler case of motion parallax due to a sensor moving through an otherwise stationary environment. We then show how the approach can be extended to identify which side of a dynamic occlusion boundary corresponds to the occluding surface. The fundamental principal involved is that at an occlusion boundary, the image of the surface boundary moves with the image of the occluding surface. Such information is important in interpreting dynamic scenes. Results are demonstrated on optical flow fields automatically computed from real image sequences.     

一种基于PSO的改进光流算法

针对变分光流法无法有效检测由间断、遮挡等因素造成的错误光流分量的缺陷,提出一种基于PSO(Particle Swarm Optimization)的光流算法。该方法在Classic+NL算法模型的基础上计算出光流后,引入前向光流和后向光流的运动一致性理论来判断遮挡区域,并通过基于PSO的修补法来实现对遮挡区域错误光流的有效修补,同时,利用邻域光流修补法实现了再次修补。实验结果表明,该方法能有效克服由间断、遮挡等因素造成的错误光流分量的缺陷,更准确地刻画出光流,提高光流的计算精度。     

A mathematical model for computer image tracking

A mathematical model using an operator formulation for a moving object in a sequence of images is presented. Time-varying translation and rotation operators are derived to describe the motion. A variational estimation algorithm is developed to track the dynamic parameters of the operators. The occlusion problem is alleviated by using a predictive Kalman filter to keep the tracking on course during severe occlusion. The tracking algorithm (variational estimation in conjunction with Kalman filter) is implemented to track moving objects with occasional occlusion in computer-simulated binary images.