System and method for importance sampling of area lights in participating media

摘要

Provided are systems and methods that address the problem of single scattering in homogeneous volumes. In one implementation, an importance sampling technique is provided that avoids a singularity near point light sources. The system and method can be extended to the situation of area lights of arbitrary shapes. The error caused by the non-constant distance to the finite-extent area light is distributed by using random sample points within the area light as points from which lighting is calculated for sampling points along the ray.

主权项

1. A method of rendering a scene, the scene including a homogeneous participating media illuminated by a light source, comprising:
a. defining a virtual ray extending from a point or pixel on a virtual viewing plane; b. defining a series of sampling points along the virtual ray, the sampling points spaced equi-angularly with respect to a light source; c. calculating a contribution to an image at the point or pixel from each sampling point due to illumination through a homogeneous participating media, wherein the sampling points are arranged according to a distribution:
ti=D tan [(1−ηi)θa+ηiθb)] for ηiε[0,1)i. wherein ti is a distance along the ray at which point “i” is located;ii. D is an orthogonal distance from the light source to the virtual ray;iii. θa and θb are angles between an orthogonal projection of the light source onto the virtual ray and a line from the light source to the points a and b on the ray, respectively; andiv. ηi is a random number between [0,1); and d. rendering an image based on the calculated contributions.