One of the major problems in Monte Carlo based methods for global illumination is noise. This paper investigates adaptive sampling as a method to alleviate the problem. We introduce a new refinement criterion, which takes human perception and limitations of display devices into account by incorporating the tone-operator. Our results indicate that this can lead to a significant reduction in the overall RMS-error, and even more important that noisy spots are eliminated. This leads to a very homogeneous image quality.
As most adaptive sampling techniques our method is biased. In order to investigate the importance of this problem, a nonparametric bootstrap method is presented to estimate the actual bias. This provides a technique for bias correction and it shows that the bias is most significant in areas with indirect illumination.
Rasmus Tamstorf and Henrik Wann Jensen: "Adaptive Sampling and Bias Estimation in Path Tracing". In "Rendering Techniques '97". Eds. J. Dorsey and Ph. Slusallek. Springer-Verlag, pp. 285-295, 1997