(The Eurographics Association, 2015) Manzi, Marco; Kettunen, Markus; Aittala, Miika; Lehtinen, Jaakko; Durand, Frédo; Zwicker, Matthias; Jaakko Lehtinen and Derek Nowrouzezahrai
Gradient-domain path tracing has recently been introduced as an efficient realistic image synthesis algorithm. This paper introduces a bidirectional gradient-domain sampler that outperforms traditional bidirectional path tracing often by a factor of two to five in terms of squared error at equal render time. It also improves over unidirectional gradient-domain path tracing in challenging visibility conditions, similarly to how conventional bidirectional path tracing improves over its unidirectional counterpart. Our algorithm leverages a novel multiple importance sampling technique and an efficient implementation of a high-quality shift mapping suitable for bidirectional path tracing. We demonstrate the versatility of our approach in several challenging light transport scenarios.