
Physically Based Rendering, fourth edition: From Theory to Implementation: Pharr, Matt, Jakob, Wenzel, Humphreys, Greg: 9780262048026: Amazon.com: Books,

Amazon | Physically Based Rendering: From Theory to Implementation | Pharr, Matt, Jakob, Wenzel, Humphreys, Greg | Rendering & Ray Tracing,

Physically Based Rendering, fourth edition: From Theory to Implementation: Pharr, Matt, Jakob, Wenzel, Humphreys, Greg: 9780262048026: Amazon.com: Books,

Ray tracing made possible on 42-year-old ZX Spectrum: 'reasonably fast, if you consider 17 hours per frame to be reasonably fast' | PC Gamer,

Physically based rendering - Wolfire Games Blog,