A wave optics based fiber scattering model
A wave optics based fiber scattering model
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DOI：
10.1145/3414685.3417841
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发表时间：
2020-11
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影响因子：
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通讯作者：
Mengqi Xia;B. Walter;E. Michielssen;D. Bindel;Steve Marschner
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文献类型：
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作者：
Mengqi Xia;B. Walter;E. Michielssen;D. Bindel;Steve Marschner
渲染中现有的光纤散射模型都是基于通过光纤几何形状追踪光线，但对于小光纤来说，衍射和干扰是不可忽略的，因此依赖光线光学可能会导致外观错误。本文提出了第一个基于波动光学的光纤散射模型，引入了来自全波模拟的方位角散射函数。求解平面波照射的恒定横截面直光纤的麦克斯韦方程可简化为求解 2D 域中的 3D 电磁场，而我们的光纤散射模拟器使用边界元法 (BEM) 有效地解决了这个 2.5D 问题。根据产生的场，我们计算消光、吸收和远场散射分布，我们用它们来模拟路径追踪器中光纤的阴影和散射。我们根据波模拟和对单根纺织纤维衍射测量的模拟来验证我们的路径追踪器。我们的结果表明，我们的方法可以复制具有不同尺寸、横截面和材料特性的各种纤维，包括纺织纤维、动物毛皮和人类头发。渲染包括色彩效果、锐利特征的柔化以及传统基于光线的模型无法预测的强前向散射，尽管这两种方法在许多条件下为复杂的光纤组件产生相似的外观。
Existing fiber scattering models in rendering are all based on tracing rays through fiber geometry, but for small fibers diffraction and interference are non-negligible, so relying on ray optics can result in appearance errors. This paper presents the first wave optics based fiber scattering model, introducing an azimuthal scattering function that comes from a full wave simulation. Solving Maxwell's equations for a straight fiber of constant cross section illuminated by a plane wave reduces to solving for a 3D electromagnetic field in a 2D domain, and our fiber scattering simulator solves this 2.5D problem efficiently using the boundary element method (BEM). From the resulting fields we compute extinction, absorption, and far-field scattering distributions, which we use to simulate shadowing and scattering by fibers in a path tracer. We validate our path tracer against the wave simulation and the simulation against a measurement of diffraction from a single textile fiber. Our results show that our approach can reproduce a wide range of fibers with different sizes, cross sections, and material properties, including textile fibers, animal fur, and human hair. The renderings include color effects, softening of sharp features, and strong forward scattering that are not predicted by traditional ray-based models, though the two approaches produce similar appearance for complex fiber assemblies under many conditions.