Color-rendering indices in global illumination methods

摘要

Human perception of material colors depends heavily onnthe nature of the light sources that are used for illumination. Onenand the same object can cause highly different color impressionsnwhen lit by a vapor lamp or by daylight, respectively. On the basis ofnstate-of-the-art colorimetric methods, we present a modern ap-nproach for the calculation of color-rendering indices (CRI), whichnwere defined by the International Commission on Illumination (CIE)nto characterize color reproduction properties of illuminants. We up-ndate the standard CIE method in three main points: first, we use thenCIELAB color space; second, we apply a linearized Bradford trans-nformation for chromatic adaptation; and finally, we evaluate colorndifferences using the CIEDE2000 total color difference formula.nMoreover, within a real-world scene, light incident on a measure-nment surface is composed of a direct and an indirect part. Neumannnand Schanda [Proc. CGIV’06 Conf., Leeds, UK, pp. 283–286n(2006)] have shown for the cube model that diffuse interreflectionsncan influence the CRI of a light source. We analyze how color-nrendering indices vary in a real-world scene with mixed direct andnindirect illumination and recommend the usage of a spectral render-ning engine instead of an RGB-based renderer for reasons of accu-nracy of CRI calculations.