基于环境映照自动对齐的高质量虚实融合技术

要实现高品质的增强现实效果需要解决虚拟物体与现实场景的光照一致性问题.虽然采用HDR技术能获取场景的环境映照,但需要解决所获取的光照环境信息与真实场景的对齐问题.为此提出一种基于特征自动匹配的环境映照对齐方法.首先采用Affine-SIFT算法和随机抽样一致性算法对环境映照和拍摄场景进行特征匹配并优化匹配结果,然后利用基于运动推断结构的摄像机定标算法求得匹配对的三维位置,从而计算出环境映照与真实场景的对应关系,实现了二者的自动对齐.基于该技术搭建的高真实感实时虚实融合系统采用基于关键帧的相机跟踪技术,可以实时地将虚拟物体注册到拍摄的视频场景里,并允许对其进行实时的交互编辑.在渲染时有效地利用了自动对齐后的光照环境信息,采用重要性采样算法和阴影映射技术实现了实时的高质量渲染.实验结果表明,所搭建的增强现实系统很好地解决了实时虚实融合中的几何一致性和光照一致性问题.     

基于增强现实的虚拟实景空间的研究与实现

增强现实可以把计算机产生的虚拟物体或其他信息合成到用户看到的真实场景中．本文将增强现实技术与基于图像的绘制技术有机的结合起来，研究并实现了一个基于增强现实技术的虚拟实景空间系统．首先介绍了虚拟实景空间的构造，然后着重探讨了虚拟物体与实景空间的合成方法，主要解决合成中的几何一致性和光照一致性问题。     

实景空间中虚拟对象嵌入技术研究

实景空间是以实景图像为素材构造出的具有三维操纵能力的虚拟空间,增强现实技术可以把计算机产生的虚拟物体或其他信息合成到用户看到的真实场景中。该文主要讨论如何在实景空间中嵌入计算机生成的虚拟对象。首先介绍了实景空间的概念和模型,然后着重探讨了虚拟对象与实景空间的合成方法,主要解决合成中的几何一致性和光照一致性问题。     

增强现实中的光照一致性研究

增强现实中的光照一致性是确保虚拟物体和真实场景很好融合的关键,它能使计算机模拟出的虚拟物体与真实场景相融合后显得更加真实。因此需要根据真实场景中光照分布情况,对虚拟物体做阴影处理,从而消除虚拟物体的飘浮感。针对动态场景中的高实时性要求,对现有的光照估计算法进行改进,并应用聚类算法对光源进行筛选,较好地解决了动态环境下虚实场景的光照一致性问题。实验结果表明,采用所提出的改进算法,能够得到逼真的阴影视觉效果,同时系统具有良好的实时性。     

基于图像的光照模型的研究与实现

为了把计算机生成的虚拟物体更好地融入真实场景的实拍照片中，实现光照一致性的效果，提出了一个基于图像的光照模型，它使用光测图作为光源从而实现对场景的照明。在研究基于图像的局部光照模型时，又提出了双向折射率分布函数这一概念，从而简化了局部光照模型的设计。在实现阶段，采用立方体环境映照来表示场景，采用光测图记录环境映照中光辐射的分布信息，从而提高了绘制效率。实验表明，本模型较成功地实现了光照一致性，在增强现实、图像合成等方面具有很大的应用价值。     

基于WTK的数据手套交互控制模块设计与实现

依据虚拟现实中数据手套操纵的虚拟手与虚拟场景的交互控制过程，在VC 环境下，设计了一个基于WTK的数据手套交互控制模块，重点研究其中的虚拟手手势合成技术和交互操作中的碰撞检测技术。提出用平行节点数据结构组织虚拟手模型，用空间图形变换法实现手势合成；结合包围盒和多边形碰撞检测法，研究了虚拟手与虚拟场景的碰撞检测。应用结果显示，虚拟手可动态地呈现与人手基本一致的手势，能够比较逼真地实现了虚拟手抓取物体、释放物体等交互操作。     

用于增强现实的光照估计研究综述

增强现实技术将计算机生成的虚拟物体实时叠加到用户周围的真实场景中,虚拟物体与真实环境拥有一致的光照效果是该技术的难点之一.光照一致性研究包括光照估计、材质表面反射属性估计以及真实感渲染等内容,其中光照估计是光照一致性的先决条件,结合材质表面反射属性可以保证虚实物体一致的光照渲染效果.文中概述了增强现实中光照一致性研究的最新进展,通过分析现有技术的优缺点阐述了当前光照估计研究所面临的主要挑战,同时展望了该领域未来的发展方向.     

增强现实技术在虚拟演播室系统中的应用

虚拟演播室是虚拟现实技术和视频合成技术相结合的产物,其场景是计算机生成的三维场景,由于人们对虚拟场景和复杂度的无限要求,使得场景的实时显示十分困难,使用基于图像的绘制技术构造虚拟空间能够较好地解决这个问题。在虚拟演播室中,演员需要与三维运动虚拟物体进行交互,运用增强现实技术,可以将三维虚拟物体与基于图象绘制的虚拟场景融合在一起。     

增强现实光照方向估计方法评述与展望

光照一致性是增强现实中实现虚实融合的重要方面,实时地估计出户外场景中的光照方向,对实现户外场景光照一致性和增强真实感具有重要意义.针对光照方向估计问题,首先归纳了户外场景光照方向估计的特点,把现有的光照方向估计方法分为借助光测球等特殊标定物的估算方法、立体视觉法和人工智能法3类方法.然后总结了各类方法的基本原理和有代表性的研究工作,并且比较了各类方法的优缺点和适用范围.最后,根据实际应用中存在的问题和挑战,展望了户外增强现实系统光照方向估计的研究方向.     

基于Direct3D的虚拟场景光照技术研究

虚拟现实技术中真实感图形的生成,已经成为计算机图形学研究的重要内容之一,在虚拟场景中,合理使用光照技术能够增强物体的真实感。本文分析了在Direct3D程序中如何通过光照技术增加虚拟场景中物体的真实感,并通过实际代码研究了虚拟场景中光照技术的具体实现过程。     

Interactive 3D content insertion in images for multimedia applications

This article addresses the problem of creating interactive mixed reality applications where virtual objects interact in images of real world scenarios. This is relevant to create games and architectural or space planning applications that interact with visual elements in the images such as walls, floors and empty spaces. These scenarios are intended to be captured by the users with regular cameras or using previously taken photographs. Introducing virtual objects in photographs presents several challenges, such as pose estimation and the creation of a visually correct interaction between virtual objects and the boundaries of the scene. The two main research questions addressed in this article include, the study of the feasibility of creating interactive augmented reality (AR) applications where virtual objects interact in a real world scenario using the image detected high-level features and, also, verifying if untrained users are capable and motivated enough to perform AR initialization steps. The proposed system detects the scene automatically from an image with additional features obtained using basic annotations from the user. This operation is significantly simple to accommodate the needs of non-expert users. The system analyzes one or more photos captured by the user and detects high-level features such as vanishing points, floor and scene orientation. Using these features it will be possible to create mixed and augmented reality applications where the user interactively introduces virtual objects that blend with the picture in real time and respond to the physical environment. To validate the solution several system tests are described and compared using available external image datasets.     

Interactive virtual relighting of real scenes

Computer augmented reality (CAR) is a rapidly emerging field which enables users to mix real and virtual worlds. Our goal is to provide interactive tools to perform common illumination, i.e., light interactions between real and virtual objects, including shadows and relighting (real and virtual light source modification). In particular, we concentrate on virtually modifying real light source intensities and inserting virtual lights and objects into a real scene; such changes can be very useful for virtual lighting design and prototyping. To achieve this, we present a three-step method. We first reconstruct a simplified representation of real scene geometry using semiautomatic vision-based techniques. With the simplified geometry, and by adapting recent hierarchical radiosity algorithms, we construct an approximation of real scene light exchanges. We next perform a preprocessing step, based on the radiosity system, to create unoccluded illumination textures. These replace the original scene textures which contained real light effects such as shadows from real lights. This texture is then modulated by a ratio of the radiosity (which can be changed) over a display factor which corresponds to the radiosity for which occlusion has been ignored. Since our goal is to achieve a convincing relighting effect, rather than an accurate solution, we present a heuristic correction process which results in visually plausible renderings. Finally, we perform an interactive process to compute new illumination with modified real and virtual light intensities     

水彩画风格实时增强现实技术

在传统的AR系统中,虚拟物体和真实场景在视觉上存在较为明显的差异,达不到虚拟物体和真实场景无缝结合的要求。将增强现实技术与NPR有机地结合起来,减小这种视觉差异,研究并实现了水彩画风格的增强现实系统。     

Lighting Simulation of Augmented Outdoor Scene Based on a Legacy Photograph

We propose a novel approach to simulate the illumination of augmented outdoor scene based on a legacy photograph. Unlike previous works which only take surface radiosity or lighting related prior information as the basis of illumination estimation, our method integrates both of these two items. By adopting spherical harmonics, we deduce a linear model with only six illumination parameters. The illumination of an outdoor scene is finally calculated by solving a linear least square problem with the color constraint of the sunlight and the skylight. A high quality environment map is then set up, leading to realistic rendering results. We also explore the problem of shadow casting between real and virtual objects without knowing the geometry of objects which cast shadows. An efficient method is proposed to project complex shadows (such as tree's shadows) on the ground of the real scene to the surface of the virtual object with texture mapping. Finally, we present an unified scheme for image composition of a real outdoor scene with virtual objects ensuring their illumination consistency and shadow consistency. Experiments demonstrate the effectiveness and flexibility of our method.     

基于标志点注册及探测球的光源追踪算法

增强现实系统中,解决虚拟物体表面光照情况与真实环境匹配问题关键的一步是进行光源追踪。基于标志点注册及具有漫反射特性的探测球提出一种光源追踪算法。该算法仅对一幅被单一光源照射的标志立方体和探测球图像进行分析,利用图中标志点确定探测球相对照相机的位置、姿态关系,利用探测球表面的亮度信息推算光源向量。该探测球图像要进行一系列图像处理程序,其中等亮度线的提取及拟合是关键步骤。实验结果表明,本文算法能够达到预期效果,较好地实现了光源追踪,适用于各种位置的单一光源照射情况及基于标志点注册的增强现实系统。     

Harmonic rendering for visual coherence on mobile outdoor AR environment

Rapid developments in augmented reality (AR) and related technologies have led to increasing interest in immersive content. AR environments are created by combining virtual 3D models with a real-world video background. It is important to merge these two worlds seamlessly if users are to enjoy AR applications, but, all too often, the illumination and shading of virtual objects is not consider the real world lighting condition or does not match that of nearby real objects. In addition, visual artifacts produced when blending real and virtual objects further limit realism. In this paper, we propose a harmonic rendering technique that minimizes the visual discrepancy between the real and virtual environments to maintain visual coherence in outdoor AR. To do this, we introduce a method of estimating and approximating the Sun’s position and the sunlight direction to estimate the real sunlight intensity, as this is the most significant illumination source in outdoor AR and it provides a more realistic lighting environment for such content, reducing the mismatch between real and virtual objects.

     

Making Imperfect Shadow Maps View‐Adaptive: High‐Quality Global Illumination in Large Dynamic Scenes

We propose an algorithm to compute interactive indirect illumination in dynamic scenes containing millions of triangles. It makes use of virtual point lights (VPL) to compute bounced illumination and a point‐based scene representation to query indirect visibility, similar to Imperfect Shadow Maps (ISM). To ensure a high fidelity of indirect light and shadows, our solution is made view‐adaptive by means of two orthogonal improvements: First, the VPL distribution is chosen to provide more detail, that is, more dense VPL sampling, where these contribute most to the current view. Second, the scene representation for indirect visibility is adapted to ensure geometric detail where it affects indirect shadows in the current view.     

基于图像分解的光照估计算法

增强现实技术的目的在于将计算机生成的虚拟物体叠加到真实场景中。实现良好的虚实融合需要对场景光照进行估算,针对高光场景,利用场景中的不同反射光信息对场景进行有效的光照估计,首先通过基于像素聚类方法的图像分解对图像进行反射光的分解,得到漫反射图和镜面反射图,对漫反射图进行进一步的本征图像分解,得到反照率图和阴影图;之后结合分解结果和场景深度对输入图像的光照信息进行计算;最后使用全局光照模型对虚拟物体进行渲染,可以得到虚实场景高度融合的光照效果。     

Instant Caching for Interactive Global Illumination

The ability to interactively render dynamic scenes with global illumination is one of the main challenges in computer graphics. The improvement in performance of interactive ray tracing brought about by significant advances in hardware and careful exploitation of coherence has rendered the potential of interactive global illumination a reality. However, the simulation of complex light transport phenomena, such as diffuse interreflections, is still quite costly to compute in real time. In this paper we present a caching scheme, termed Instant Caching, based on a combination of irradiance caching and instant radiosity. By reutilising calculations from neighbouring computations this results in a speedup over previous instant radiosity‐based approaches. Additionally, temporal coherence is exploited by identifying which computations have been invalidated due to geometric transformations and updating only those paths. The exploitation of spatial and temporal coherence allows us to achieve superior frame rates for interactive global illumination within dynamic scenes, without any precomputation or quality loss when compared to previous methods; handling of lighting and material changes are also demonstrated.