Correlated visibility sampling for direct illumination

State-of-the-art importance sampling strategies for direct illumination take into account the importance of the incident illumination, as well as the surface BRDF. Hence, these techniques achieve low variance in unoccluded regions. However, the resulting images still have noise in partially occluded regions as these techniques do not take visibility into account during the sampling process. We introduce the notion of correlated visibility sampling, which considers visibility in partially occluded regions during the sampling process, thereby improving the quality of the shadowed regions. We aim to draw samples in the partially occluded regions according to the triple product of the incident illumination, BRDF and visibility using Monte Carlo sampling followed by Metropolis sampling.