An analytic model for full spectral sky-dome radiance

Abstract

We present a physically-based analytical model of the daytime sky. Based on the results of a first-principles brute force simulation of radiative transfer in the atmosphere, we use the same general approach of fitting basis function coefficients to radiance data as the Perez and Preetham models do. However, we make several modifications to this process, which together significantly improve the rendition of sunsets and high atmospheric turbidity setups -- known weak points of the Preetham model. Additionally, our model accounts for ground albedo, and handles each spectral component independently. The latter property makes it easily extensible to the near ultraviolet range of the spectrum, so that the daylight appearance of surfaces that include optical brighteners can be properly predicted. Due to its similar mathematical properties, the new model can be used as a drop-in replacement of the Preetham model.

A framework for the experimental comparison of solar and skydome illumination

“…The turbidity for the clear sky was found from the closest weather station for that day. Wherever possible, we directly integrate the author's source code into their own Mitsuba plug-ins [Preetham et al 1999;Bruneton and Neyret 2008;Hosek and Wilkie 2012;Hosek and Wilkie 2013]. The other models ( [Nishita et al 1993;Nishita et al 1996;Haber et al 2005] were carefully implemented from their respective papers to the best of our ability.…”

Sky Based Light Metering for High Dynamic Range Images

“…We compared several zenith luminance models and developed a trigonometric interpolation between two of them to obtain higher accuracy over a wider range of sun elevation angles. Additionally, we performed a comparison of the well-known Perez sky model with its recent extension [HW12] in the context of our work.…”

“…Recently, an extension for the Perez and Preetham sky models was suggested by Hosek and Wilki [HW12]. This new model gives an improvement over the Perez sky model in modelling the sky appearance for lower solar elevation angles, as well as the appearance of the circumsolar ring.…”

“…Absolute values are required when one is interested in materials behaviour under different lighting conditions. The use of light probes would be beneficial over rendered skies [PSS99, HW12] due to variety of sky conditions, which cannot be reproduced by analytical sky-models.…”

“…Comparison of magnitudes of relative errors for images with clear sky regions from Fairchild's dataset[Fai07] in cases of Perez [PSM93] and Hosek and Wilkie[HW12] sky models using weighted combination of Karayel and Soler zenith models. More comparison results can be found in the supplemental.…”