Tunable Bounding Volumes for Monte Carlo Applications

Luminaire sampling plays an important role in global illumination calculation using Monte Carlo integration. A conventional approach generates samples on the surface of the luminaire, resulting in rendered images with high variance of noise. In this paper, we present an efficient solid angle sampling technique using tunable bounding volumes for global illumination calculation. In contrast to the conventional approach, our technique derives samples from the solid angle subtended by the luminaire. In the construction process, we build a convex, frustum-like polyhedron as a bounding volume for a light source. Front-facing polygons of the bounding volume are then projected onto the unit hemisphere around the shaded point. These projected polygons represent the approximated solid angle subtended by the luminaire. The third step samples the projected spherical polygons on which a number of stratified samples are generated. We employ various types of light sources including ellipse, elliptic cylinder, elliptic cone and elliptic paraboloid. We perform our technique for Monte Carlo Direct Lighting and Monte Carlo Path Tracing applications. Under similar sample numbers, our technique produces images with less variance of noise compared to the conventional method. In addition, our technique provides roughly equal image quality in less execution time. Our approach is simple, efficient, and applicable to many types of luminaries for global illumination calculation.