Simulating multiple scattering in hair using a photon mapping approach
Simulating multiple scattering in hair using a photon mapping approach
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DOI：
10.1145/1179352.1141995
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发表时间：
2006-07
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影响因子：
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通讯作者：
Jonathan T. Moon;Steve Marschner
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文献类型：
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作者：
Jonathan T. Moon;Steve Marschner
正确模拟多重散射对于准确渲染头发非常重要。然而，大量头发是一个难以模拟的场景，因为来自单个纤维的散射非常结构化且向前定向，并且因为许多此类散射事件产生的辐射分布仍然具有相当的方向性。由于这些原因，以前的方法无法比蒙特卡罗路径追踪更快地计算准确的图像。本文提出了一种基于以前的体积光子映射方法的新的物理精确的毛发渲染方法。第一遍通过追踪头发几何体中的粒子来生成光子图，将它们沿着路径而不是散射事件沉积。第二遍光线追踪头发，计算直接照明并在光子贴图中查找间接辐射率。光子在 5D 位置方向空间中存储和查找，以实现头发中发生的非常定向的辐射分布。与新的纤维辐射缓存方法一起，我们的方法可以有效且低噪声地模拟头发中的困难散射问题。新算法针对路径追踪进行了验证，并与真实头发中的光散射照片进行了比较。
Simulating multiple scattering correctly is important for accurate rendering of hair. However, a volume of hair is a difficult scene to simulate because scattering from an individual fiber is very structured and forward directed, and because the radiance distributions that arise from many such scattering events remain quite directional. For these reasons, previous methods cannot compute accurate images substantially faster than Monte Carlo path tracing.This paper proposes a new physically accurate method for rendering hair that is based on previous volumetric photon mapping methods. The first pass generates a photon map by tracing particles through the hair geometry, depositing them along paths rather than at scattering events. The second pass ray traces the hair, computing direct illumination and looking up indirect radiance in the photon map. Photons are stored and looked up in 5D position-direction space to allow for the very directional radiance distributions that occur in hair. Together with a new radiance caching method for fibers, our method simulates difficult scattering problems in hair efficiently and with low noise.The new algorithm is validated against path tracing and also compared with a photograph of light scattering in real hair.