Color-rendering indices in global illumination methods

Human perception of material colors depends heavily on the nature of the light sources that are used for illumination. One and the same object can cause highly different color impressions when lit by a vapor lamp or by daylight, respectively. On the basis of state-of-the-art colorimetric methods, we present a modern ap- proach for the calculation of color-rendering indices (CRI), which were defined by the International Commission on Illumination (CIE) to characterize color reproduction properties of illuminants. We up- date the standard CIE method in three main points: first, we use the CIELAB color space; second, we apply a linearized Bradford trans- formation for chromatic adaptation; and finally, we evaluate color differences using the CIEDE2000 total color difference formula. Moreover, within a real-world scene, light incident on a measure- ment surface is composed of a direct and an indirect part. Neumann and Schanda (Proc. CGIV'06 Conf., Leeds, UK, pp. 283-286 (2006)) have shown for the cube model that diffuse interreflections can influence the CRI of a light source. We analyze how color- rendering indices vary in a real-world scene with mixed direct and indirect illumination and recommend the usage of a spectral render- ing engine instead of an RGB-based renderer for reasons of accu- racy of CRI calculations. © 2009 SPIE and

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