Browsing by Author "d'Eon, Eugene"

Now showing 1 - 3 of 3
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    An Analytic BRDF for Materials with Spherical Lambertian Scatterers
    (The Eurographics Association and John Wiley & Sons Ltd., 2021) d'Eon, Eugene; Bousseau, Adrien and McGuire, Morgan
    We present a new analytic BRDF for porous materials comprised of spherical Lambertian scatterers. The BRDF has a single parameter: the albedo of the Lambertian particles. The resulting appearance exhibits strong back scattering and saturation effects that height-field-based models such as Oren-Nayar cannot reproduce.
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    A Position-Free Path Integral for Homogeneous Slabs and Multiple Scattering on Smith Microfacets
    (The Eurographics Association and John Wiley & Sons Ltd., 2022) Bitterli, Benedikt; d'Eon, Eugene; Ghosh, Abhijeet; Wei, Li-Yi
    We consider the problem of multiple scattering on Smith microfacets. This problem is equivalent to computing volumetric light transport in a homogeneous slab. Although the symmetry of the slab allows for significant simplification, fully analytic solutions are scarce and not general enough for most applications. Standard Monte Carlo simulation, although general, is expensive and leads to variance that must be dealt with. We present the first unbiased, truly position-free path integral for evaluating the BSDF of a homogeneous slab. We collapse the spatially-1D path integral of previous works to a position-free form using an analytical preintegration of collision distances. Evaluation of the resulting path integral, which now contains only directions, reduces to simple recursive manipulation of exponential distributions. Applying Monte Carlo to solve the reduced integration problem leads to lower variance. Our new algorithm allows us to render multiple scattering on Smith microfacets with less variance than prior work, and, in the case of conductors, to do so without any bias. Additionally, our algorithm can also be used to accelerate the rendering of BSDFs containing volumetrically scattering layers, at reduced variance compared to standard Monte Carlo integration.
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    Zero-variance Transmittance Estimation
    (The Eurographics Association, 2021) d'Eon, Eugene; Novák, Jan; Bousseau, Adrien and McGuire, Morgan
    We apply zero-variance theory to the Volterra integral formulation of volumetric transmittance.We solve for the guided sampling decisions in this framework that produce zero-variance ratio tracking and next-flight ratio tracking estimators. In both cases, a zero-variance estimate arises by colliding only with the null particles along the interval. For ratio tracking, this is equivalent to residual ratio tracking with a perfect control. The next-flight zero-variance estimator is of the collision type and can only produce zero-variance estimates if the random walk never terminates. In drawing these new connections, we enrich the theory of Monte Carlo transmittance estimation and provide a new rigorous path-stretching interpretation of residual ratio tracking.