Importance sampling for volumetric illumination of flames

► According to the extinction properties of flames, we propose a new extinction coefficient hierarchy to rapidly estimate the extinction of voxel lights in given direction. ► We propose a new metric to measure the similarity of voxel lights based on their illumination and average extinction. ► For each pixel to be shaded, we can accurately estimate the product distribution of the surface BRDF and the volumetric illumination using the importance adjustment algorithm for clusters.