基于模板跟踪的实时无标志点注册算法

为了解决不依赖于标志点的增强现实系统的环境注册问题,提出了一种基于选定模板跟踪的无标志点注册算法。该算法使用已标定的单目摄像机进行场景捕捉,通过对运动目标上的选定模板进行实时跟踪,获得每帧场景图像中的对应特征,利用透射投影变换计算运动区域的单应性约束后,再结合摄像机内参数,完成对目标的3维姿态估计,从而得到场景的3维环境注册信息。实现了一种基于该算法的无标志点的增强现实系统。介绍了系统结构和工作流程,试验结果验证了理论的正确性和系统的鲁棒性。     

计算机生成图形的光照效果模型

对光源进行了分类,从材质表面特性和多光源照射的效果出发分析了顶点的颜色、亮度值与光源和其相对位置的关系,最后对算法进行了分析和综合。该算法提高了图像生成系统的逼真度,但运算量较大。     

一种基于视沉的增强现实三维注册算法

为了提高增强现实系统三维注册的精度和效率，提出了一种基于计算机视觉的增强现实三维注射算法，并已将其用于采用透射式头盔显示器的增强现实系统中，该算法有如下特点：（1）构架简单，实用性强，一般情况下只需4个平面标志物就可实现三维注册；（2）工作范围大，甚至可以应用到室外的增强现实系统中；（30数值求解过程最线性过程，误差小，可以满足增强现实系统高精度三维注册的要求，另外，应用这种算法所需要作的图象处理计算量很小，其典型系统包括一个彩色CCD和几个不同颜色的标志点，由于很容易获得标志点的对应像面位置，而且不需要计算图象对，因此实时性好，是一般图形工作站和PC机上的增强现实系统进行实时注册的算法基础。     

面向增强现实的多传感器组合位姿注册算法

持续稳定的准确注册是构建增强现实系统的关键,为提高跟踪注册的稳定性和精度,提出了一种基于互补滤波(CF)和无迹卡尔曼滤波(UKF)的多传感器融合注册方案.该算法采用互补滤波器融合陀螺仪、加速度计和地磁感应计数据估计摄像头姿态;在处理视觉图像时,结合惯性姿态数据进行图像特征匹配;利用UKF融合视觉和惯性数据进行摄像头位置估计.实验表明:该算法在跟踪稳定性、精度、效率和抗干扰能力均优于传统的基于扩展卡尔曼滤波(EKF)的融合算法.     

移动增强现实中视觉三维注册方法的实现

为了提高移动增强现实注册技术的性能,采用了一种基于计算机视觉的注册算法。该方法利用ARToolkit中的标识检测法查找相关的标识和特征点,然后基于视觉三维注册算法得到模型视图矩阵,最后在相应位置绘制虚拟物体。实验结果表明这种注册方法在实时性、稳定性、抗遮挡性方面效果良好,满足移动增强现实系统高精度三维注册的要求。     

一种基于近似点光源模型的光度立体视觉系统 标定方法

文章研究了一种由近似点光源组成的光度立体视觉系统的标定方法。由于光源自身的非均匀发光特性,传统的平行光和点光源模型不再适用,为实现精确的三维法向重建,必须对光源及光照场进行精确的标定。论文首先根据光源自身的发光特性建立其辐射度模型,进而提出了一种两步标定策略,对光源位置参数及主光轴参数进行标定。以相机作为参照系,提出了一种多球标定方法,用于计算各个光源的位置参数,该方法利用相机观察到的多个球面高光点图像坐标,结合球体轮廓线及球体半径实现了光源位置的精确计算。为实现光源主光轴参数的估算,提出了一种基于参考平面的标定方法,通过分析近似点光源照射下的平面亮度分布,结合等亮度线拟合策略实现了光源主光轴方向参数的计算。基于系统标定参数以及光源的发光模型,就可以对每个场景点的入射光条件进行精确建模,从而实现精确的法向计算。在实验部分,分别对标准几何物体和自由曲面物体进行三维重建实验,并与传统的平行光及点光源模型进行了对比。结果显示,所提出的标定方法能够在非均匀光照条件下获得精确的三维法向重建结果。     

基于光电检测技术的电缆表面缺陷实时监测系统研究

基于光电检测技术开发了电缆表面缺陷实时监测系统。在硬件结构方面,系统采用半环形LED白光源照射电缆,利用线阵CCD相机采集电缆表面图像。在软件算法方面,提出一种改进的ROI (Region of Interest)算法精确定位电缆区域,利用一种基于改进双边滤波的图像差分算法建立背景模型,改进一种基于CV-Kmeans区域分类自适应滤波窗口算法来凸显电缆表面缺陷特征。研究结果表明,基于光电检测技术研发的电缆表面缺陷实时监测系统的识别能力较高,整体监测准确率不低于97.0%。     

基于仿射重投影的增强现实三维注册方法

针对增强现实虚实配准中的无标志点虚实场景注册问题,提出一种基于仿射重投影与自然特征点追踪相结合的虚实注册方法.该方法以仿射变换为桥梁来建立欧氏空间下的摄像机坐标系与世界坐标系之间的变换关系,它与OpenGL等当前流行的图形渲染工具一致,具有更强的通用性;采用基于分类的自然特征匹配策略,能够在视角和视点发生大幅度变化情况下依然正常工作;提出基于特征点集合的仿射坐标系定义方法,使增强现实系统在最小配置下只需4点追踪成功即可完成注册,比需要6点的透视投影方法具有更好的健壮性和精确性.实验结果表明,该方法的运算速度能够达到18帧/s,具有较好的实时性;同时注册误差保持在5mm以内,达到令人满意的配准精度.     

亮度补偿变换矩阵的颜色恒常性算法

颜色恒常性是计算机视觉的重要研究方向,旨在准确识别目标的真实颜色而不受场景光源变化的影响。目前提出的多种颜色恒常性算法,使用传统的Von Kries 对角变换矩阵对图像的估计照明进行校正,对低照度和强光照射条件下采集到的图像处理效果比较差。根据图像形成的数学模型和光学原理提出了亮度补偿对角变换矩阵的颜色恒常计算方法,该方法对图像颜色校正的同时根据图像像素亮度变化对图像的亮度进行补偿。通过采用多种颜色恒常性算法进行实验验证,该方法能够有效地校正低照度和强光照射图像的颜色、对比度和亮度,从而增强了图像的视见度。     

基于视觉的增强现实运动跟踪算法

增强现实系统不仅具有虚拟现实的特点同时具有虚实结合的新特性，为实现虚拟物体与真实物体间的完善结合，必须实时地动态跟踪摄像与真实物体间的相对位置和方向，建立观测模,墼是而通过动态三维显示技术迅速地将虚拟物体添加到真实物体之上，然而目前大多数增强现实系统的注册对象均匀静物体，运动物体的注册跟踪尚很少有人涉足。该算法通过标志点的光流场估计真实环境中运动物体的运动参数，根据透视投影原理和刚体的运动特性确定摄像机与运动物体间的相对位置和方向，实现增强现实系统的运动目标跟踪注册。该算法构架简单、实时性强，易于实现，扩展了增强现实系统的应用范围。     

基于CV／CAD的三维物体几何建模

在虚拟现实等技术领域中,都涉及到由现实世界中的实际景物建立对应的计算机描述的虚拟景物的问题,为此提出了利用计算机视觉与CAD几何建模技术相结合的三维珠体建模途径,首先通过编码光栅方法获取三维物体的深度图象,并采用数学形态学的方法加以分割,然后利用代数曲面拟合手段对分割后的三维曲面片进行重建,并使用CAD几何建模工具由重建的曲面片构成物体的几何模型,该文给出了初步的实验结果,证明所提出的技术途径基本可行。     

虚拟环境建模及实时性改善方法

提出了虚拟现实软件实现方法的概念,利用交互方式的,比较,阐明了虚拟现实与仿真的区别,通过计算机三维实体造型和真实感环境泻染技术,实现了虚拟环境建模,通过融入增强现实的思想,把握虚实结合尺度,将基于图象的方法与基于建模的相结合,从而改善了眯拟环境下交互的实时性。     

Multiple light source detection

This paper presents the V2R algorithm, a novel method for multiple light source detection using a Lambertian sphere as a calibration object. The algorithm segments the image of the sphere into regions that are each illuminated by a single virtual light and subtracts the virtual lights of adjacent regions to estimate the light source vectors. The algorithm uses all pixels within a region to form a robust estimate of the corresponding virtual light. The circumstances under which the light source detection problem lacks a unique solution are discussed in detail and the way in which the V2R algorithm resolves the ambiguity is explained. The V2R algorithm includes novel procedures for identifying the critical lines that bound the regions, for estimating the light source vectors, and for identifying opposite light pairs. Experiments are performed on synthetic and real images and the performance of the V2R algorithm is compared to that of a recent algorithm from the literature. The experimental results demonstrate that the proposed algorithm is robust and that it gives substantially improved accuracy.     

Multiple illuminant direction detection with application to imagesynthesis

Pentland observed (1982, 1984) that the human eye is sensitive to the change of intensities. On an image of a smooth surface, the change of intensities is maximal whenever the illuminant direction is perpendicular to the normal of the surface. This motivates us to introduce the concept of critical points, where the surface normal is perpendicular to some light source direction. Apparently, the illuminant direction has a simple geometric relationship with the corresponding critical points. In this paper, for simplicity reasons, we restrict our discussions to the shading of a Lambertian sphere of known size in a multiple distant light source environment. A novel global representation of the intensity function is derived. Based on this intensity characterization, the least-squares and iteration techniques are used to determine critical points and, thus, the light source directions and their intensities if certain conditions are satisfied. The performance of this new approach is evaluated using both synthetic images and real images. As an application, we use it as a tool to determine light sources in real image synthesis. The experimental results show that this technique can be used to superimpose synthetic objects with a real scene     

Difference sphere: An approach to near light source estimation

We present a novel approach for estimating light sources from a single image of a scene that is illuminated by major near point light sources, a few directional light sources and ambient light. We propose to employ a pair of reference spheres as light probes and introduce the difference sphere that we acquire by differencing the intensities of two image regions of the reference spheres. Because the effect by directional light sources and ambient light is eliminated by differencing, the key advantage of considering the difference sphere is that it enables us to identify near point light sources including their radiant intensities. We also show that analysis of gray level contours on spherical surfaces facilitates separate identification of multiple combined light sources and is well suited to the difference sphere. We demonstrate the effectiveness of the entire algorithm with experimental results while also investigating the applicability to an open scanner in indoor scene.     

图像亮度线索下的单目深度信息提取

目的 深度信息的获取是3维重建、虚拟现实等应用的关键技术,基于单目视觉的深度信息获取是非接触式3维测量技术中成本最低、也是技术难度最大的手段。传统的单目方法多基于线性透视、纹理梯度、运动视差、聚焦散焦等深度线索来对深度信息进行求取,计算量大,对相机精度要求高,应用场景受限,本文基于固定光强的点光源在场景中的移动所带来的物体表面亮度的变化,提出一种简单快捷的单目深度提取方法。方法 首先根据体表面反射模型,得到光源照射下的物体表面的辐亮度,然后结合光度立体学推导物体表面辐亮度与摄像机图像亮度之间的关系,在得到此关系式后,设计实验,依据点光源移动所带来的图像亮度的变化对深度信息进行求解。结果 该算法在简单场景和一些日常场景下均取得了较好的恢复效果,深度估计值与实际深度值之间的误差小于10%。结论 本文方法通过光源移动带来的图像亮度变化估计深度信息,避免了复杂的相机标定过程,计算复杂度小,是一种全新的场景深度信息获取方法。     

基于镜面成像技术的三维立体视觉测量与重构综述

利用镜面成像技术获取被测物体或场景的三维信息得到研究者越来越多的关注。光线与平面镜或曲面镜交互时产生镜面成像。平面镜的反射属性可以改善视觉效果,基于光路射线展开过程可应用于不同的平面镜成像系统,采用光路展开替代镜面交互应用于三维场景,得到虚拟三维空间,平面镜成像使得复杂的射线交互可以用一种虚拟的方式可视化,且坐标系统的变化容易跟踪。曲面镜成像通常不具有透视投影属性,根据曲面的曲率来改变空间显示。曲面镜常常导致折反射,故针对不同的三维立体视觉测量及重构需设计相应的几何恢复算法。从计算机图形学和计算机视觉的角度,分析了镜面成像的基本原理,对近年来较典型的基于镜面成像技术的三维测量与重构方法及最新研究进展进行综述。     

An interactive handheld spherical 3D object display system

Traditional display systems usually display 3D objects on static screens (monitor, wall, etc.) and the manipulation of virtual objects by the viewer is usually achieved via indirect tools such as keyboard or mouse. It would be more natural and direct if we display the object onto a handheld surface and manipulate it with our hands as if we were holding the real 3D object. In this paper, we propose a prototype system by projecting the object onto a handheld foam sphere. The aim is to develop an interactive 3D object manipulation and exhibition tool without the viewer having to wear spectacles. In our system, the viewer holds the sphere with his hands and moves it freely. Meanwhile we project well-tailored images onto the sphere to follow its motion, giving the viewer a virtual perception as if the object were sitting inside the sphere and being moved by the viewer. The design goal is to develop a low-cost, real-time, and interactive 3D display tool. An off-the-shelf projector-camera pair is first calibrated via a simple but efficient algorithm. Vision-based methods are proposed to detect the sphere and track its subsequent motion. The projection image is generated based on the projective geometry among the projector, sphere, camera and the viewer. We describe how to allocate the view spot and warp the projection image. We also present the result and the performance evaluation of the system.     

An Improved Virtual Spherical Lights Approach for Glossy Illumination

Based on a virtual spherical light source method, this paper presents an improved virtual spherical lights approach for glossy illumination by modifying a reflection render equation. First, in order to keep primitive spherical lights, it uses non-zero solid angle integration instead of a geometric item of traditional Instant Radiosity arithmetic. Second, the formula mode for the light energy allocation of VSLs is improved by the energy distribution, in which the radius of sphere is replaced by the radius of inscribed circle generated by the tangent to the non-zero solid angle of cone. Third, the similar function of judging two point visibility takes place of a cosine term in the approximate equations of the VSLs. Experiments show that blurring or disappearing phenomenon that appear in part of right-angle surface scene is avoided.