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、仿真系统、娱乐和广告等不同领域的重要问题。计算机图像生成的一个重要的、很大程度上尚未探索的领域是模拟风化及其对外观的影响。风化是环境与物质相互作用的结果。当前的材料计算机图形模型基于理想化表面的物理特性，这些表面表现出理想的漫反射、光泽反射或镜面反射。然而，这种理想化的材料很少存在并且很难生产。为了使这种理想化的材料看起来逼真，动画师和建模师经常应用许多纹理。不幸的是，这种纹理贴图的使用是非常特别和劳动密集型的，并且它与理想化模型的使用相冲突。我们需要的是基于物理的真实的材料模型，这些模型包含了它们可能的生命史，因此也包含了可能的外观。该项目的目标是设计新的材料计算机模型，这些模型可以随着时间的推移保持一系列外观。通过NSF-CAREER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。在这个基于实现的更新（ABR）提案中，我们简要总结了建立在我们最初工作基础上的几个新方向，包括几种额外材料的研究和建模，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，以及在具有复杂内部结构的材料中呈现光传输的技术。这项工作有可能大大扩展合成图像的视觉真实感，并通过提供基本的，复杂的模型，材料和过程，影响其随时间变化的外观，减少对繁琐的特设技术的依赖。除了工作的重要性，在计算机图形学，这项研究应该有利于科学可视化，建筑和保护，广告，娱乐，艺术品修复，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学领域增加新的维度。

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.