15 research outputs found
A Dual-Beam Method-of-Images 3D Searchlight BSSRDF
We present a novel BSSRDF for rendering translucent materials. Angular
effects lacking in previous BSSRDF models are incorporated by using a dual-beam
formulation. We employ a Placzek's Lemma interpretation of the method of images
and discard diffusion theory. Instead, we derive a plane-parallel
transformation of the BSSRDF to form the associated BRDF and optimize the image
confiurations such that the BRDF is close to the known analytic solutions for
the associated albedo problem. This ensures reciprocity, accurate colors, and
provides an automatic level-of-detail transition for translucent objects that
appear at various distances in an image. Despite optimizing the subsurface
fluence in a plane-parallel setting, we find that this also leads to fairly
accurate fluence distributions throughout the volume in the original 3D
searchlight problem. Our method-of-images modifications can also improve the
accuracy of previous BSSRDFs.Comment: added clarifying text and 1 figure to illustrate the metho
Importance Sampling Microfacet-Based BSDFs using the Distribution of Visible Normals
International audienceWe present a new approach to microfacet-based BSDF importance sampling. Previously proposed sampling schemes for popular analytic BSDFs typically begin by choosing a microfacet normal at random in a way that is independent of direction of incident light. To sample the full BSDF using these normals requires arbitrarily large sample weights leading to possible fireflies. Additionally, at grazing angles nearly half of the sampled normals face away from the incident ray and must be rejected, making the sampling scheme inefficient. Instead, we show how to use the distribution of visible normals directly to generate samples, where normals are weighted by their projection factor toward the incident direction. In this way, no backfacing normals are sampled and the sample weights contain only the shadowing factor of outgoing rays (and additionally a Fresnel term for conductors). Arbitrarily large sample weights are avoided and variance is reduced. Since the BSDF depends on the microsurface model, we describe our sampling algorithm for two models: the V-cavity and the Smith models. We demonstrate results for both isotropic and anisotropic rough conductors and dielectrics with Beckmann and GGX distributions
A Generalized Ray Formulation For Wave-Optics Rendering
Under ray-optical light transport, the classical ray serves as a local and
linear "point query" of light's behaviour. Such point queries are useful, and
sophisticated path tracing and sampling techniques enable efficiently computing
solutions to light transport problems in complex, real-world settings and
environments. However, such formulations are firmly confined to the realm of
ray optics, while many applications of interest, in computer graphics and
computational optics, demand a more precise understanding of light. We
rigorously formulate the generalized ray, which enables local and linear point
queries of the wave-optical phase space. Furthermore, we present sample-solve:
a simple method that serves as a novel link between path tracing and
computational optics. We will show that this link enables the application of
modern path tracing techniques for wave-optical rendering, improving upon the
state-of-the-art in terms of the generality and accuracy of the formalism, ease
of application, as well as performance. Sampling using generalized rays enables
interactive rendering under rigorous wave optics, with orders-of-magnitude
faster performance compared to existing techniques.Comment: For additional information, see
https://ssteinberg.xyz/2023/03/27/rtplt