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Practical Product Path Guiding Using Linearly Transformed Cosines

In In Computer Graphics Forum (Proceedings of Eurographics Symposium on Rendering 2020)

Equal-time com­par­is­ons (2 minutes). Our meth­od re­duces noise com­pared to Müller et al. [MGN17], by ef­fi­ciently guid­ing paths­based on the product of the BSDF and in­com­ing ra­di­ance at each path ver­tex. We show Mean Ab­so­lute Er­ror (MAE)

Abstract

Path tra­cing is now the stand­ard meth­od used to gen­er­ate real­ist­ic im­agery in many do­mains, e.g., film, spe­cial ef­fects, ar­chi­tec­ture etc. Path guid­ing has re­cently emerged as a power­ful strategy to counter the no­tori­ously long com­pu­ta­tion times re­quired to render such im­ages. We present a prac­tic­al path guid­ing al­gorithm that per­forms product sampling, i.e., samples pro­por­tion­al to the product of the bi­d­irec­tion­al scat­ter­ing dis­tri­bu­tion func­tion (BSDF) and in­com­ing ra­di­ance. We use a spa­tial-dir­ec­tion­al sub­di­vi­sion to rep­res­ent in­com­ing ra­di­ance, and in­tro­duce the use of Lin­early Trans­formed Co­sines (LTCs) to rep­res­ent the BSDF dur­ing path guid­ing, thus en­abling ef­fi­cient product sampling. Des­pite the com­pu­ta­tion­al ef­fi­ciency of LTCs, sev­er­al op­tim­iz­a­tions are needed to make our meth­od cost ef­fect­ive. In par­tic­u­lar, we show how we can use vec­tor­iz­a­tion, pre­com­pu­ta­tion, as well as strategies to op­tim­ize mul­tiple im­port­ance sampling and Rus­si­an roul­ette to im­prove per­form­ance. We eval­u­ate our meth­od on sev­er­al scenes, demon­strat­ing con­sist­ent im­prove­ment in ef­fi­ciency com­pared to pre­vi­ous work, es­pe­cially in scenes with sig­ni­fic­ant glossy inter-re­flec­tion.

Text citation

Stavros Diolatzis, Adrien Gruson, Wenzel Jakob, Derek Nowrouzezahrai, and George Drettakis. 2020. Practical Product Path Guiding Using Linearly Transformed Cosines. In In Computer Graphics Forum (Proceedings of Eurographics Symposium on Rendering) 39(4).

BibTeX
@article{Diolatzis2020Practical,
    author = {Stavros Diolatzis and Adrien Gruson and Wenzel Jakob and Derek Nowrouzezahrai and George Drettakis},
    title = {Practical Product Path Guiding Using Linearly Transformed Cosines},
    journal = { In Computer Graphics Forum (Proceedings of Eurographics Symposium on Rendering) },
    volume = {39},
    number = {4},
    year = {2020},
    month = jul
}