Alexei G. Voloboy, Dmitry D. Zhdanov, Sergei V. Ershov
Pages 39–47

When simulating the propagation of light, luminance/ radiance brought by a ray is calculated from the optical properties of the scene objects it interacts with. According to their optical properties, objects can be roughly divided into diffuse and specular. In Monte Carlo ray tracing luminance/radiance is calculated only for diffuse surfaces. When a ray hits a specular a surface, it is reflected (or refracted) until it reaches a diffuse surface, and only then the luminance/radiance is calculated. In the proposed approach, diffuse elements are further divided into genuine diffuse and quasispecular elements. The most natural criterion for the latter is that it scatters light in a narrow cone about the specular direction. An element of the scene can also be a superposition of both types when its scattering function is a sum of the genuine diffuse and quasispecular parts. This article shows how different components of illuminance/irradiance interact with quasispecular objects and describe how this works in the bidirectional stochastic ray tracing. The proposed approach significantly reduces stochastic noise for multiple scenes. This method is also applicable for simulation of volume scattering, treating the phase function of the medium as quasispecular. In this case, the choice of quasispecular objects is not based on the nature of the bidirectional scattering distribution function (BSDF): the medium is treated as completely quasispecular while the surfaces, even if their BSDFs are narrower, remain genuine diffuse. The article shows the advantage of this approach.
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