lightsample

Lightsample is a concept in computer graphics and optical simulation referring to the process of selecting sample directions and light sources to estimate the illumination at a shading point. In rendering, lightsampling is a key component of evaluating the rendering equation using Monte Carlo methods.

Two broad categories are commonly used: light-source sampling and direction sampling. Light-source sampling picks individual light sources and draws samples of their emission that can reach the shading point, often accommodating visibility and attenuation. Direction sampling selects directions within the hemisphere around the point to estimate incoming radiance, which can be particularly useful for environment lighting.

Techniques used to implement lightsampling include uniform sampling, importance sampling (sampling from the light distribution or the BRDF), and multiple importance sampling (MIS), which combines sampling strategies to reduce variance. For area lights, samples are taken over the light's surface; for environment maps, the sampling distribution is often prefiltered or importance-weighted by luminance.

Applications include physically based rendering, where accurate lightsampling improves realism and reduces noise in global illumination. It also underpins real-time rendering approximations, such as light probes and precomputed radiance transfer.

Challenges include variance and noise, especially in scenes with many small lights or complex caustics, and the computational cost of evaluating visibility and shadow rays. Effective lightsampling often relies on architectural data structures and acceleration techniques.

See also: global illumination, Monte Carlo integration, ray tracing, BRDF, environment mapping.