Adaptive path tracing

Here are some experiments in adaptive path tracing with the light cache; the adaptation is unbiased, meaning that it does not alter the final image result as far as physical correctness is concerned (although there is a little bias introduced by the light cache itself). For all images, the regular and adaptive version were traced with the same number of subdivisions for the light cache. In most cases, the fact that adaptive ppt can put more samples in important directions gives a better result than regular ppt. This is especially obvious in the cases of GI caustics where a large portion of the illumination at a point comes from a small part of the hemisphere above it.

	Regular ppt	Adaptive ppt
The visible portion of the scene is lit entirely by indirect light. The light distribution in the adaptive image is a little smoother.
GI caustics from an area light source. The adaptive image is smoother.
Only light sources are the sun and sky; the caustics of the sunlight onto the wall are better in the adaptive image and the light distribution is better.
Cornell box with water. In the regular ppt image, the caustics are not seen through the water surface itself, while the adaptive image is more correct.