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 at equal sample counts. Incorporating the product to additionally capture the foreshortening term and optimizing in a multiple-importance-sampling-aware manner results in further reduced noise. Primary-sample-space path-sampling techniques offer little to no benefit over unidirectional path tracing with our NPS slightly outperforming PSSPS [Guo et al. 2018] with an equal number of samples.