Stratified Wavelength Clusters for Efficient Spectral Monte Carlo Rendering

Wavelength dependent Monte Carlo rendering can correctly and generally capture effects such as spectral caustics (rainbows) and chromatic abberation. It also improves the colour accuracy of reflectance models and of illumination effects such as colour bleeding and metamerism. The stratified wavelength clustering (SWC) strategy carries several wavelength stratified radiance samples along each light transport path. The cluster is split into several paths or degraded into a single path only if a specular refraction at the surface of a dispersive material is encountered along the path. The overall efficiency of this strategy is high since the fraction of clusters that need to be split or degraded in a typical scene is low, and also because specular dispersion tends to decrease the source colour variance, offseting the increased amortized cost of generating each path.