https://www.fxguide.com/quicktakes/v-rays-practical-stochastic-rendering-of-spec-y-things/?utm_source=fxguide+web+form&utm_campaign=3eeeb1948d-fxg_rss&utm_medium=email&utm_term=0_172378485e-3eeeb1948d-108782797&mc_cid=3eeeb1948d&mc_eid=8be05f8e94
Chaos Group guide to stochastic rendering