Computer Graphics Techniques for Modeling and Rendering Weathered Materials

图像合成是建筑、照明和工业设计、科学可视化、模拟系统、娱乐和广告等多个领域的重要问题。计算机图像生成的一个重要的、在很大程度上未被探索的领域是风化及其对外观的影响的模拟。风化是环境与物质相互作用的结果。当前材料的计算机图形学模型是基于呈现理想漫反射、光泽或镜面反射的理想化表面的物理。然而，这种理想化的材料很少存在，也很难生产。为了使这种理想化的材质看起来逼真，动画师和建模师经常应用许多纹理。不幸的是，纹理贴图的这种使用是非常特别和劳动密集型的，并且它与使用理想化模型相冲突。所需要的是真实材料的物理模型，其中包含了它们可能的生活史，因此也包含了可能的外观。这个项目的目标是设计一种新的材料计算机模型，这种材料可以随着时间的推移保持一系列的外观。通过NSF职业奖，我们在这个问题上取得了重大进展，并为未来的工作建立了关键的基础设施。在这个基于成就的更新(ABR)提案中，我们简要总结了几个新的方向，这些方向建立在我们最初工作的基础上，包括几种附加材料的研究和建模、影响外观的环境因素的模拟、表面表示和相互作用模式、测量设备，以及在复杂内部结构的材料中渲染光传输的技术。这项工作有可能极大地扩展合成图像的视觉真实感，并通过为影响其随时间变化的外观的材质和过程提供基本的、复杂的模型来减少对繁琐的特别技术的依赖。除了这项工作在计算机图形学中的重要性外，这项研究还应该有助于科学可视化、建筑与保护、广告、娱乐、艺术修复、汽车设计、地质学、土木工程和环境科学等应用。由于该项目借鉴了其他几个学科的材料，如应用数学、地质学、材料科学、光学和物理学，它有望为计算机图形领域增加新的维度。

Image synthesis is an important problem for such diverse fields as architecture, lighting and industrial design, scientific visualization, simulation systems, entertainment, and advertising. An important, largely unexplored area of computer image generation is the simulation of weathering and its effects on appearance. Weathering results from the interaction of the environment with the materials in the world. Current computer graphics models of materials are based on the physics of idealized surfaces that exhibit ideal diffuse, glossy, or specular reflection. However, such idealized materials rarely exist and are hard to produce. In order to make such idealized materials look realistic, animators and modelers often apply many textures. Unfortunately, this use of texture maps is very ad hoc and labor intensive, and it is in conflict with the use of idealized models. What is needed are physically-based models of real materials that incorporate their possible life histories, and hence, possible appearances. The goal of this project is to devise new computer models of materials that can sustain a range of appearances over time. Through an NSF-CAREER award, we have made significant headway on this problem and built critical infrastructure for future work. In this Accomplishment-Based Renewal (ABR) proposal, we provide a brief summary of several new directions that build on our initial work, including the study and modeling of several additional materials, simulations of environmental factors that affect appearance, surface representations and modes of interaction, a measurement device, and techniques for rendering light transport in materials with complex internal structures. This work has the potential to greatly expand the visual realism of synthetic images and reduce the reliance on tedious ad hoc techniques by providing fundamental, sophisticated models for materials and the processes that affect their time-varying appearance. In addition to the work's importance in computer graphics, this research should benefit such applications as scientific visualization, architecture and preservation, advertising, entertainment, art restoration, automotive design, geology, civil engineering, and environmental sciences. Because the project draws on material from several other disciplines such as applied math, geology, materials science, optics, and physics, it promises to add new dimensions to the field of computer graphics.