基于环境光场和漫反射光场的动态场景绘制

利用光强的可叠加性,本文提出了将光场分解为不随场景变化的子光场的思想,使得物体、光源、观察点都可自由变动的动态场景绘制也能利用基于图象的绘制技术之优势。依靠漫反射与观察方向的无关性,本文还提出了漫反射光场的四维表示法,并且利用物体对不同点光源的漫反射之间以及环境光与漫反射光之间的内在联系,只用一个单位强度的单色点光源为物体构造漫反射光场,从而节省了存储空间和预处理时间。利用其数据结构的一致性,环境光场、漫反射光场和深度场中对应点的数据被合并成５维矢量以便更有效地压缩。本文给出的绘制算法,能准确地计算出物体的颜色和场景中阴影的变化等动态场景的典型特征,从而为在低档计算机实现动态场景的实时绘制提供了理论和技术依据。     

一种基于多边形柱面全景图的虚拟漫游新方法

提出了一种基于图像绘制的多边形柱面全景图的虚拟漫游方法.利用普通的手持相机在一个多边形区域内沿某一路径拍摄并拼接多幅全景图,通过基于SIFT的特征点检测来计算深度,用狭缝图像插值来实现整个区域内的平滑漫游.该方法具有采样简单、虚拟场景真实感强,支持连续大范围漫游的特点.     

基于图象的室内虚拟漫游系统

基于图象的绘制（Image Based Rendering)作为一种全新的图形绘制方式,以其相对于传统几何绘制而言,具有高效实用的优点,近年来得到了研究人员越来越多的关注,但IBR技术仍存在一些主要难点,如图象的无缝拼接和实时漫游。针对此问题,开发了一个基于部分球面模型的室内虚拟漫游系统。该系统采用自动匹配和人机交互相结合的方法,可以无缝地将多幅照片拼接成一张全景图,同时采用一种改进的基于查找表的算法,实现了固定视点的实时漫游。     

基于图像的虚拟景观漫游

提出一种基于图像的虚拟景观漫游方法。该方法采用全景图和基于图像的动画来建立虚拟环境,用户通过实时图像处理浏览器,可以模拟这两种典型的漫游行为－环绕漫游和贯穿漫游,并且在风景旅游模拟系统（Virtrual-Touring)中实现了这种方法。     

基于图像的虚拟场景实时漫游

提出一种基于图像的并行绘制算法 ,通过分割图像显示窗口并行绘制 ,实现了三维场景的高分辨率图像的实时绘制 该算法按各节点计算性能分配任务 ,实现了负载平衡 利用三维场景漫游时相邻帧之间的相关性 ,采用RLE(RunLengthEncoded)压缩方法传输图像 ,降低了传输开销 实验结果表明 ,在 4台PC组成的机群上 ,实现了5 12× 5 12大小的图像的实时绘制     

基于图像的实时漫游

提出了一个点和多边形模型混合的场景表达方式,从而实现了对复杂场景的视点不受限制的实时漫游.它从多幅带深度的参考图像出发,在预处理阶段区别对待场景中平面物体和曲面物体在参考图像中的对应像素.对于在参考图像所占区域较大的空间平面,用传统的多边形模型方式对其进行表达,试图恢复出其平面方程,然后通过采样密度比较和重采样过程,将该空间平面在所有参考图像中的出现合并成一个均匀采样的纹理图像;而对于空间曲面或在参考图像中所占面积较小的平面,使用点的形式对其进行表达,通过采样密度的比较去掉冗余的点,将保留下来的点按其空间位置进行聚类.同时,对于场景中那些不被所有参考图像所拍摄到而在漫游过程中可能形成空洞的部分,提出一个空洞预填补技术,在预处理阶段即对这类空洞进行填补,从而大大减少了漫游阶段出现空洞的几率.在漫游阶段则使用纹理映射和点Warping的方式进行绘制,以充分利用图形硬件的加速功能.     

基于照片的环绕漫游

本文着重研究了基于照片的环绕漫游模拟技术,给出了一种以三维重建为核心的旅游模拟方法,对摄像机参数恢复、焦点对象的三维重建以及漫游场景的生成等相关技术进行探讨,并在此基础上实现了一个用于环绕漫游模拟的实验系统──PhotoTour。     

三维虚拟场景绘制加速技术综述

加速三维图形的绘制对三维虚拟场景的交互式生成有重要作用。该文结合三维图形绘制流水线,概括了提高绘制性能的途径,综述了可见性处理、细节层次方法、基于图象的绘制以及大型几何数据库的操纵等主要的绘制加速技术。     

自适应的表面光场映射算法

随着几何获取技术和计算机视觉技术的进步,三维照相开始成为一个研究热点,而基于表面光场的绘制算法可以获得真实感很好的重建结果.本文提出了一种自适应的表面光场映射算法,使其能够自动的在采样密度、压缩率、重建质量、绘制速度上取得较好的平衡,算法以表面光场的重采样技术为基础,形成一系列二维采样矩阵,通过用户指定的重建错误率和样本的特性计算矩阵的分解次数,对矩阵进行分解,并将分解次数反馈到采样步骤中,决定新样本是否需要加入到数据库中,最后利用纹理的空间相关性对其进行类似MPEG的编码.在绘制阶段采用纹理映射算法,充分利用了图形硬件的加速功能,达到实时绘制的结果.我们对实际场景进行了试验,获得了很高的压缩比,并且在普通PC机上达到了25F/S的绘制效果.     

基于IBR的三维重建新方法

在研究普通的平面图像的基础上,基于图像渲染(IBR)提出了一种新的建立立体模型的方式。能对普通的平面单幅图像进行特征点提取,从而半自动地生成所需要的立体效果。该方法直接从图像中提取信息,渲染出具有照片真实感的模型。实验结果表明,利用该系统渲染的三维模型准确真实,能够满足虚拟现实等应用的需要。     

A Geometric Analysis of Light Field Rendering

Recently, many image-based modeling and rendering techniques have been successfully designed to render photo-realistic images without the need for explicit 3D geometry. However, these techniques (e.g., light field rendering (Levoy, M. and Hanrahan, P., 1996. In SIGGRAPH 1996 Conference Proceedings, Annual Conference Series, Aug. 1996, pp. 31–42) and Lumigraph (Gortler, S.J., Grzeszczuk, R., Szeliski, R., and Cohen, M.F., 1996. In SIGGRAPH 1996 Conference Proceedings, Annual Conference Series, Aug. 1996, pp. 43–54)) may require a substantial number of images. In this paper, we adopt a geometric approach to investigate the minimum sampling problem for light field rendering, with and without geometry information of the scene. Our key observation is that anti-aliased light field rendering is equivalent to eliminating the double image artifacts caused by view interpolation.Specifically, we present a closed-form solution of the minimum sampling rate for light field rendering. The minimum sampling rate is determined by the resolution of the camera and the depth variation of the scene. This rate is ensured if the optimal constant depth for rendering is chosen as the harmonic mean of the maximum and minimum depths of the scene. Moreover, we construct the minimum sampling curve in the joint geometry and image space, with the consideration of depth discontinuity. The minimum sampling curve quantitatively indicates how reduced geometry information can be compensated by increasing the number of images, and vice versa. Experimental results demonstrate the effectiveness of our theoretical analysis.     

An interactive 3D medical visualization system based on a light field display

We present a prototype medical data visualization system exploiting a light field display and custom direct volume rendering techniques to enhance understanding of massive volumetric data, such as CT, MRI, and PET scans. The system can be integrated with standard medical image archives and extends the capabilities of current radiology workstations by supporting real-time rendering of volumes of potentially unlimited size on light field displays generating dynamic observer-independent light fields. The system allows multiple untracked naked-eye users in a sufficiently large interaction area to coherently perceive rendered volumes as real objects, with stereo and motion parallax cues. In this way, an effective collaborative analysis of volumetric data can be achieved. Evaluation tests demonstrate the usefulness of the generated depth cues and the improved performance in understanding complex spatial structures with respect to standard techniques.

基于Java 3D的医学图像三维重建系统

系统采用分层组件化的设计思想,在逻辑上分为三层:图像预处理层、图像分割层和用户界面层,实现了医学图像的二维标注与测量、三维体数据的分割、三维重建与交互功能。介绍了系统的体系结构和系统开发的主要技术方法。最后指出了系统的实用性和对医学研究方面的价值。     

Relighting with the Reflected Irradiance Field: Representation,Sampling and Reconstruction

Image-based relighting (IBL) is a technique to change the illumination of an image-based object/scene. In this paper, we define a representation called the reflected irradiance field which records the light reflected from a scene as viewed at a fixed viewpoint as a result of moving a point light source on a plane. It synthesizes a novel image under a different illumination by interpolating and superimposing appropriate recorded samples. Furthermore, we study the minimum sampling problem of the reflected irradiance field, i.e., how many light source positions are needed. We find that there exists a geometry-independent bound for the sampling interval whenever the second-order derivatives of the surface BRDF and the minimum depth of the scene are bounded. This bound ensures that when the novel light source is on the plane, the error in the reconstructed image is controlled by a given tolerance, regardless of the geometry. We also analyze the bound of depth error so that the extra reconstruction error can also be governed when the novel light source is off-plane. Experiments on both synthetic and real surfaces are conducted to verify our analysis.     

Live 3D Video in Soccer Stadium

This paper proposes a method to realize a 3D video system that can capture video data from multiple cameras, reconstruct 3D models, transmit 3D video streams via the network, and display them on remote PCs. All processes are done in real time. We represent a player with a simplified 3D model consisting of a single plane and a live video texture extracted from multiple cameras. This 3D model is simple enough to be transmitted via a network. A prototype system has been developed and tested at actual soccer stadiums. A 3D video of a typical soccer scene, which includes more than a dozen players, was processed at video rate and transmitted to remote PCs through the internet at 15–24 frames per second.     

3D coordinates measurement based on structured light sensor

This paper mainly discusses several challenges in exploiting a structured light sensor to realize 3D coordinates measurement: a practical and flexible sensor structure is proposed with accuracy analysis, a very robust and accurate line extraction method is adopted to localize the center of the light stripe under considerable disturbances, the invariance of double cross-ratio based method is used to obtain enough accurate calibration points and a novel planar target based calibration method is presented. An application system of the structured light sensor for tyre inspection is set up, and the real online measurement results show that the application system has good repeatability and accuracy.     

针对光场图像的多尺度抗混叠绘制方法

针对现有光场图像存在混叠的问题,提出一种多尺度抗混叠绘制光场图像的方法.首先分析了光场角度降采样引起图像混叠的原因,然后给出角度采样率与图像混叠关系的数学描述,并且指出了影响图像混叠的相关因素.在此基础上,提出采用多尺度光场图像梯度融合的方法降低图像混叠,其优点在于无需场景深度先验信息.分别在虚拟光场数据和真实光场数据集上进行了抗混叠绘制实验,结果表明该方法优于经典光场绘制方法,能够得到与已知深度绘制方法相近的结果.