"Experimental Analysis of Multiple Scattering BRDF Models"
Feng Xie, James Bieron, Pieter Peers, and Pat Hanrahan

Siggraph Asia Technical Communications, December 2021
In this paper, inspired by Ngan et al.’s experimental analysis of 7 single scattering BRDF models, we present the first comprehensive experimental analysis of multiple scattering BRDF models, using both a traditional cosine weighted L2 BRDF fitting metric as well as an image based adaptive metric on the MERL material database. We show that, although physically based multiple scattering BRDF models slightly reduce fitting errors for rough materials, the perceptual visual difference between multiple scattering BRDF models and a standard GGX BRDF model is negligible for the majority of measured materials. Our experiments show that a blend of a Lambertian and a GGX lobe can fit most of the rough MERL materials well, except for a few materials that exhibit phenomena beyond the capabilities of a microfacet BRDF model (with or without multiple scattering), such as inter-fiber scattering (in fabrics), or complex subsurface scattering in between the top coating layer and the diffuse substrate.

Supplementary Material
author = {Xie, Feng and Bieron, James and Peers, Pieter and Hanrahan, Pat},
title = {Experimental Analysis of Multiple Scattering BRDF Models},
month = {December},
year = {2021},
booktitle = {Siggraph Asia Technical Communications},