Environment Mapping
Here I tackle doing lighting using Environment Maps in PBRT, a ray-tracer.
Here is the environment map I used:
Here is a final Rendering, using importance sampling, and 3x3 Anti-Aliasing: (ROLL OVER for PointLight)
Cool right? That is using 4.6k importance sampled lighting rays and 9 eye-rays per pixel.
I also experimented with the relatively speed with which the image cleans up. I found that jittering didn't really help too much.
RollOver to compare 1k lighting rays per pixel. The jittered makes the shadow better, but makes for more high-frequency noise.
Importance sampling helped alot, but since I implemented it using rejection sampling, it was very slow to find samples. (Gibbs sampling anyone?). Importance sampling samples the areas in the environment map which contribute more light to Buddha with more frequency, thus you need fewer rays to get a good idea how the whole thing should look.
Roll over to compare 256 samples Importance vs Uniform
That's about it, you can download all the different approaches and sample counts in one 1.2mb zip if you are so inclined.