Title: Quantifying the Error of Light Transport Algorithms
Authors: Celarek, Adam 
Wenzel, Jakob 
Wimmer, Michael  
Lehtinen, Jaakko 
Category: Original Research Article
Issue Date: 30-Jul-2019
Journal: Computer Graphics Forum 
ISSN: 0167-7055
This paper proposes a new methodology for measuring the error of unbiased physically based rendering algorithms. The current state of the art includes mean squared error (MSE) based metrics and visual comparisons of equal‐time renderings of competing algorithms. Neither is satisfying as MSE does not describe behavior and can exhibit significant variance, and visual comparisons are inherently subjective. Our contribution is two‐fold: First, we propose to compute many short renderings instead of a single long run and use the short renderings to estimate MSE expectation and variance as well as per‐pixel standard deviation. An algorithm that achieves good results in most runs, but with occasional outliers is essentially unreliable, which we wish to quantify numerically. We use per‐pixel standard deviation to identify problematic lighting effects of rendering algorithms. The second contribution is the error spectrum ensemble (ESE), a tool for measuring the distribution of error over frequencies. The ESE serves two purposes: It reveals correlation between pixels and can be used to detect outliers, which offset the amount of error substantially.
Keywords: Rendering; Error Metric; Monte Carlo; Markov Chain Monte Carlo
DOI: 10.1111/cgf.13775
Organisation: E193-02 - Forschungsbereich Computer Graphics 
License: CC BY 4.0 CC BY 4.0
Publication Type: Article
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