A radiative transfer framework for non-exponential media
A radiative transfer framework for non-exponential media
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DOI：
10.1145/3272127.3275103
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发表时间：
2018-12
期刊：
影响因子：
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通讯作者：
Benedikt Bitterli;S. Ravichandran;T. Müller;Magnus Wrenninge;Jan Novák;Steve Marschner;Wojciech Jarosz
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文献类型：
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作者：
Benedikt Bitterli;S. Ravichandran;T. Müller;Magnus Wrenninge;Jan Novák;Steve Marschner;Wojciech Jarosz
我们发展了一种新的非指数自由飞行分布介质的体积光传输理论。来自大气科学和中子传输的最新见解表明，这种分布是在存在相关散射体的情况下产生的，这些散射体是由云凝结和分形图案形成等过程自然产生的。我们的理论将非指数路径积分表示为随机经典介质平均的结果，并引入实用模型来有效地解决由此产生的平均问题。我们的理论导致了一个广义的路径积分，它允许我们使用全面的蒙特卡罗渲染算法来处理非指数媒体，同时丰富了可实现的外观的范围。我们提出了通过利用对随机过程的工作来控制统计相关性的参数模型，并发展了一种方法来将这种未解决的相关性(以及由此产生的非指数自由飞行行为)与显式建模的宏观异质性相结合。这提供了一种强大的创作方法，其中艺术家可以自由地设计与宏观非均匀密度分开的衰减轮廓的形状，而我们的理论提供了关于路径空间积分的物理上一致的解释。我们解决了图形的重要考虑因素，包括交互和双向渲染算法，所有这些都是在存在表面和相关媒体的情况下进行的。
We develop a new theory of volumetric light transport for media with non-exponential free-flight distributions. Recent insights from atmospheric sciences and neutron transport demonstrate that such distributions arise in the presence of correlated scatterers, which are naturally produced by processes such as cloud condensation and fractal-pattern formation. Our theory formulates a non-exponential path integral as the result of averaging stochastic classical media, and we introduce practical models to solve the resulting averaging problem efficiently. Our theory results in a generalized path integral which allows us to handle non-exponential media using the full range of Monte Carlo rendering algorithms while enriching the range of achievable appearance. We propose parametric models for controlling the statistical correlations by leveraging work on stochastic processes, and we develop a method to combine such unresolved correlations (and the resulting non-exponential free-flight behavior) with explicitly modeled macroscopic heterogeneity. This provides a powerful authoring approach where artists can freely design the shape of the attenuation profile separately from the macroscopic heterogeneous density, while our theory provides a physically consistent interpretation in terms of a path space integral. We address important considerations for graphics including reciprocity and bidirectional rendering algorithms, all in the presence of surfaces and correlated media.