Indirectly Lit Cornell Box

The Indirectly Lit Cornell Box is like a regular cornell box, only that the light source is facing upward. This results in predominantly indirect diffuse light transport, challenging the efficiency of unidirectional path tracing. Due to the diffuse materials, radiance-based path guiding performs very well in this scene, with our neural path guiding (NPG-Radiance) performing the best out of the radiance-based techniques. Incorporating the product amounts to additionally capturing the cosine foreshortening term and results in further reduced noise. NPG-Product additionally features MIS-aware optimization. Primary-sample-space path-sampling techniques offer little to no benefit over unidirectional path tracing with our NPS slightly outperforming PSSPG [Guo et al. 2018].