A Practical Wave Optics Reflection Model for Hair and Fur
A Practical Wave Optics Reflection Model for Hair and Fur
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DOI：
10.1145/3592446
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发表时间：
2023-07
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影响因子：
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通讯作者：
Mengqi Xia;B. Walter;C. Hery;Olivier Maury;E. Michielssen;Steve Marschner
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作者：
Mengqi Xia;B. Walter;C. Hery;Olivier Maury;E. Michielssen;Steve Marschner
传统的纤维散射模型，基于射线光学，缺少一些重要的视觉方面的纤维外观。先前关于理想挤出的波散射的工作[Xia et al. 2020]表明，衍射产生了基于射线的模型所缺少的强前向散射和彩色效果。然而，这项工作无法包括一些重要的表面特征，如表面粗糙度和倾斜的角质层鳞片，这是已知的纤维外观的重要性。在这项工作中，我们采取了重要的一步，研究从粗糙的纤维与任意三维微观几何的波动效应。虽然现实的3D光纤的全波模拟仍然是棘手的，我们开发了一个基于物理光学近似的3D波动光学模拟器，使用基于GPU的分层算法，大大加快了计算。它模拟表面反射和衍射散射，这是目前在所有的纤维，通常占主导地位的深色着色纤维。模拟提供了一阶散射的详细图像，但用于生产渲染并不实用，因为这需要按纤维几何形状制表。为了实际处理场景中的几何变化，我们提出了一种基于小波噪声的模型，捕获与渲染相关的模拟结果中的重要统计特征。我们的模拟和实际模型都显示出与光学测量中观察到的颗粒图案相似的颗粒图案。我们紧凑的噪声模型可以轻松地与现有的散射模型相结合，以渲染各种颜色的头发和毛皮，引入视觉上重要的彩色闪光，这是所有以前的模型所缺少的。
Traditional fiber scattering models, based on ray optics, are missing some important visual aspects of fiber appearance. Previous work [Xia et al. 2020] on wave scattering from ideal extrusions demonstrated that diffraction produces strong forward scattering and colorful effects that are missing from ray-based models. However, that work was unable to include some important surface characteristics such as surface roughness and tilted cuticle scales, which are known to be important for fiber appearance. In this work, we take an important step to study wave effects from rough fibers with arbitrary 3D microgeometry. While the full-wave simulation of realistic 3D fibers remains intractable, we developed a 3D wave optics simulator based on a physical optics approximation, using a GPU-based hierarchical algorithm to greatly accelerate the calculation. It simulates surface reflection and diffractive scattering, which are present in all fibers and typically dominate for darkly pigmented fibers. The simulation provides a detailed picture of first order scattering, but it is not practical to use for production rendering as this would require tabulation per fiber geometry. To practically handle geometry variations in the scene, we propose a model based on wavelet noise, capturing the important statistical features in the simulation results that are relevant for rendering. Both our simulation and practical model show similar granular patterns to those observed in optical measurement. Our compact noise model can be easily combined with existing scattering models to render hair and fur of various colors, introducing visually important colorful glints that were missing from all previous models.