Handling occlusions in video‐based augmented reality using depth information

Augmented Reality (AR) composes virtual objects with real scenes in a mixed environment where human–computer interaction has more semantic meanings. To seamlessly merge virtual objects with real scenes, correct occlusion handling is a significant challenge. We present an approach to separate occluded objects in multiple layers by utilizing depth, color, and neighborhood information. Scene depth is obtained by stereo cameras and two Gaussian local kernels are used to represent color, spatial smoothness. These three cues are intelligently fused in a probability framework, where the occlusion information can be safely estimated. We apply our method to handle occlusions in video‐based AR where virtual objects are simply overlapped on real scenes. Experiment results show the approach can correctly register virtual and real objects in different depth layers, and provide a spatial‐awareness interaction environment. Copyright © 2009 John Wiley & Sons, Ltd.     

The role of visual occlusion in altitude maintenance during simulated flight.

The use of visual occlusion as a cue to altitude maintenance in low-altitude flight (LAF) was investigated. The extent to which the ground surface is occluded by 3-D objects varies with altitude and depends on the height, radius, and density of the objects. Participants attempted to maintain a constant altitude during simulated flight over an undulating terrain with trees of various heights, radii, and densities. As would be predicted if participants used occlusion, root-mean-square error was related to the product of tree height and tree density (Experiment 1) and to the product of tree radius and tree density (Experiment 2). This relationship was also found for simulated terrains with a more realistic mixture of tree heights (Experiment 4). The authors present a modification to an occlusion model (T. Leung & J. Malik, 1997) that can be used to approximate occlusion in the context of LAF, and they evaluate the modified model using the present LAF data. On a practical level, simulating 3-D objects is computationally expensive. The present results suggest that performance may be maintained with fewer objects if their size is increased. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Computing global visibility maps for regions on the boundaries of polyhedra using Minkowski sums

A global visibility map is a spherical image built to describe the complete set of global visible view directions for a surface. In this paper, we consider the computation of global visibility maps for regions on the boundary of a polyhedron. Both the self-occlusions introduced by a region and the global occlusions introduced by the rest of the surfaces on the boundary of the polyhedron are considered for computing a global visibility map. We show that the occluded view directions introduced between a pair of polyhedral surfaces can be computed from the spherical projection of the Minkowski sum of one surface and the reflection of the other. A suitable subset of the Minkowski sum, which shares the identical spherical projection with the complete Minkowski sum, is constructed to obtain the spherical images representing global occlusions. Our method has been successfully tested on many CAD models. It extends the previous methods for computing global visibility maps using convex decomposition, and it exhibits a better performance.     

Nd:YAG激光在泪道疾病中的应用

应用Nd:YAG泪道激光治疗机对80例(85只眼)各种泪道阻塞者进行治疗,取得较好的效果,治愈率达82.3％。手术反应轻、痛苦小、无并发症,可反复使用。     

一种基于视觉的交通检测方法

在实际交通图像检测中检测系统要面对照度变化、局部遮挡和道路阴影等问题，针对这些问题提出一种基于视觉的检测方法，实验表明新方法对解决上述问题的有效性，并在计算车辆数量和速度方面有较高的精确度和较快的执行速度。     

基于统计学习优化SIFT的面部遮挡人脸识别

针对传统的人脸识别算法受面部遮挡的影响导致很难兼顾鲁棒性和保持原始图像核心信息的问题,本文提出了一种基于统计学习优化尺度不变特征变换的面部遮挡人脸识别算法。首先,利用SIFT将所有给定训练图像用一组局部特征描述符表示出来;然后,通过执行统计学习获得正常脸部图像SIFT特征的概率分布函数,利用获得的概率分布函数在新观察到的测试图像中检测异常SIFT特征;最后,计算测试图像与训练图像之间的相似度,并利用K近邻分类器完成人脸识别。在AR人脸数据库上的实验验证了本文算法的有效性及可靠性,实验结果表明,相比其它几种较为先进的人脸识别算法,本文算法取得了更强的识别鲁棒性。     

玻璃体腔注射曲安奈德治疗视网膜分支静脉阻塞继发黄斑囊样水肿疗效观察

观察玻璃体腔注射曲安奈德(intravitreal triamcinolone acetonide,IVTA)治疗视网膜分支静脉阻塞(brach retinal vein occlusion,BRVO)继发黄斑囊样水肿(cystoid macular edema,CME)的临床效果.对33例(34眼)BRVO继发CME...     

结合语义和多层特征融合的行人检测

遮挡及背景中相似物干扰是行人检测准确率较低的主要原因. 针对该问题, 提出一种结合语义和多层特征融合(Combining semantics with multi-level feature fusion, CSMFF)的行人检测算法. 首先, 融合多个卷积层特征, 并在融合层上添加语义分割, 得到的语义特征与相应的卷积层连接作为行人位置的先验信息, 增强行人和背景的辨别性. 然后, 在初步回归的基础上构建行人二次检测模块(Pedestrian secondary detection module, PSDM), 进一步排除误检物体. 实验结果表明, 所提算法在数据集Caltech和CityPersons上漏检率(Miss rate, MR)为7.06 %和11.2 %. 该算法对被遮挡的行人具有强鲁棒性, 同时可方便地嵌入到其他检测框架.     

基于 GPU 和 Kinect 的快速物体重建

便宜的物体快速三维建模技术是当前计算机视觉领域重要的研究课题.给出了一种基于Kinect传感器的快速物体重建方法,以及基于该方法的一种图形处理器 (Graphic processing unit, GPU)原型系统实现.本文方法主要分为两步: 1)系统的初始标定; 2)全自动的物体重建.对于系统初始标定,提出了一种简单易用的粗标定方法;对于物体重建,提出一种全自动的快速物体重建方法.本文方法鲁棒性高,在出现点云配准错误时仍然能够稳定地得到较理想的重建模型.针对环闭合(Loop-closure)问题,提出了一种全局的点云配准方法.对几类物体的重建实验结果表明,本文方法方便实用,且能得到较好的重建效果.此外,本文还探索了有遮挡物体的重建问题.将本文方法应用于有遮挡物体的重建,也取得了较好的重建效果.     

综合多种预测方案实现遮挡情况下的目标跟踪

由于采用了多种运动预测方案,本文提出的目标跟踪方法能选择最佳的观测结果,实现对非标定固定焦距的静止摄像机的单目图像序列中的目标跟踪.静态背景参考图像由混合模型法估计,在最简单的环境下,跟踪算法则采用匀加速运动模型对目标完成跟踪.本文主要贡献是采用了三个预测器和最小方差相关时选择目标最可能的位置.三个预测器分别是:-跟踪方案、卡尔曼滤波和区域分割匹配方案.本跟踪方案通过具有不同遮挡情况的序列图像得到了验证.