【作者】 王骏；

【导师】 顾耀林；

【作者基本信息】 江南大学 ， 计算机应用技术， 2004， 硕士

【摘要】 合成一致性问题包括几何一致性与光照一致性两大方面,是虚拟现实、增强现实技术中经常遇到的问题。 光照一致性问题是经常涉及的一个问题。为了达到这一目的,现有的技术工作量大。一种方法根据参照物手工恢复出光源的位置,并新建一个新的虚拟光源来对虚拟物体进行照明。 本文提出了一种新的实现光照一致性的方法——基于环境映照(全景辐射度图)的光照一致性技术。本文把环境中的光照分布信息存储在环境映照(全景辐射度图)中,以此来模拟虚拟物体周围的光照环境。为此,本文提出了基于环境映照的光照模型,从理论上阐述环境映照作为光源时物体表面光亮度的计算方法。 同时,为了适用虚拟现实、增强现实对交互性的要求,本文还研究了一种基于球面谐函数的漫射环境映照滤波技术,以此来提高对环境映照预滤波的速度。 第一章是绪论,主要介绍了课题的相关背景。我们从概念、特点、组成这三个角度首先介绍了虚拟现实技术,并对近年来新出现的增强现实技术作了简单的简介。然后结合环境映照技术有代表性的研究成果介绍基于图像的绘制技术,同时引出本文所要解决的问题,即解决图形图像混合绘制时的光照一致性问题。我们列举了近年来在光照一致性的研究方面国内、外已有的相关工作,分析了它们的特点,并初步提出了本文的观点。 第二章研究了一种可用来存储真实环境中光照分布信息的新的环境映照技术——全景辐射度图技术。我们首先介绍了全景辐射度图的实现原理,包括映射原理和象素编码两个方面,并分析了其优缺点。然后结合我们的实验,给出了一种获得全景辐射度图的方法,并给出了具体的实现过程。 第三章提出了一个基于环境映照的光照模型,这是使用全景辐射度图对虚拟几何物体进行照明的理论基础。我们根据已有的若干个光照模型,从光能辐射的角度推导出了新的光亮度计算公式,并结合漫反射表面的BRDF和镜面反射表面的BRDF进行讨论。最后给出了实验结果并进行了分析。 第四章探讨了一种基于球面谐函数理论的漫射环境映照快速滤波技术。球面谐函数是定义在球面坐标系下、与傅利叶变换相类似的数学系统。我们把全景辐射度图作为二维全视函数的样本来考虑。通过使用一系列球面谐函数来近似表示这二维全视函数,从而实现滤波环境映照的快速计算。我们实现了此算法,并与已有的技术相比较,给出了实验结果的分析。 第五章是结论,同时介绍了今后的需要进一步完善的工作。更多还原

【Abstract】 Rendering computer-generated (CG) objects into real photographs is one of the most important problems in VR and AR applications. In general, such work needs recovering the real-world information, which includes camera positions and parameters, shapes, material properties, and motion of real objects.The illumination coherence is one of the key issues involved. To achieve this goal, current available techniques are labor intensive. A common technique is to manually recover the position of the light source with the help of a reference object, and to instantiate a virtual light of equal color and intensity for each real source to illuminate the CG objects.A new method, which illuminates the environment with environment maps, is proposed in this paper. We store the illumination in environment maps (light probe image) to simulate the true lighting environment. Then an illumination model based on environment maps was proposed. Meanwhile, a new fast prefiltering method for environment maps using spherical harmonics is discussed in this thesis.In Chapter 1, we first introduce the basic concepts and primary characteristics of VR systems. We also introduce AR which emerged these years briefly. Then we review the history of the use of environment maps in image-based rendering. The central topic, that is a new approach to obtain illumination coherence, is addressed in the end.In Chapter 2, we introduce the light probe image, which stores the true illumination information in environment maps. The basic principle, which includes the mapping method and pixel encoding was introduced. Meanwhile, we present a new practical approach to obtain the light probe image.In Chapter 3, we proposed an illumination model based on environment maps, which is the principle of lighting the CG objects. We illustrate the lighting computation based on photometry. The result of our experiment is also presented.In Chapter 4, we discuss a fast prefiltering method for environment maps based on spherical harmonics, which is the analogue on the sphere to the Fourier basis on the line or circle. The light probe image is a 2D plenoptic function and can be approximated by a serious of spherical harmonics. We present the implementation of the algorithm, which include the data structures and the description of some procedures. The prefiltered environment maps are also given as the result of our approach.Finally, we draw the general conclusion of this thesis in the last chapter. Future work plan on this specific topic is also included.更多还原