Ward, Greg, Elena Eydelberg-Vileshin, “Picture Perfect RGB Rendering Using Spectral Prefiltering and Sharp Color Primaries,” Thirteenth Eurographics Workshop on Rendering (2002), P. Debevec and S. Gibson (Editors).

Picture Perfect RGB Rendering Using Spectral Prefiltering and Sharp Color Primaries

Greg Ward

Exponent - Failure Analysis Associates

gward@lmi.net

Elena Eydelberg-Vileshin

Stanford University

lena@graphics.stanford.edu

Abstract

Accurate color rendering requires the consideration of many samples over the visible spectrum, and advanced rendering tools developed by the research community offer multispectral sampling towards this goal. However, for practical reasons including efficiency, white balance, and data demands, most commercial rendering packages still employ a naive RGB model in their lighting calculations. This often results in colors that are qualitatively different from the correct ones. In this paper, we demonstrate two independent and complementary techniques for improving RGB rendering accuracy without impacting calculation time: spectral prefiltering and color space selection. Spectral prefiltering is an obvious but overlooked method of preparing input colors for a conventional RGB rendering calculation, which achieves exact results for the direct component, and very accurate results for the interreflected component when compared with full-spectral rendering. In an empirical error analysis of our method, we show how the choice of rendering color space affects final image accuracy, independent of prefiltering. Specifically, we demonstrate the merits of a particular transform that has emerged from the color research community as the best performer in computing white point adaptation under changing illuminants: the Sharp RGB space.

PDF of final workshop paper (712 Kbytes)

Color Plate (389 Kbytes)

Supplemental Materials

MGF files for the test scene used in our comparisons

Materials

Room (with balls)

Fluorescent source

Tungsten source

Comparison Images (Approximation versus Full Spectral Rendering)

Lighting	Method	CIE XYZ	sRGB	Sharp
fluorescent	naïve	fluor_naive_xyz	fluor_naïve_srgb	fluor_naive_sharp
fluorescent	prefilt	fluor_approx_xyz	fluor_approx_srgb	fluor_approx_sharp
tungsten	naïve	tung_naive_xyz	tung_naïve_srgb	tung_naive_sharp
tungsten	prefilt	tung_approx_xyz	tung_approx_srgb	tung_approx_sharp
both	naïve	both_naive_xyz	both_naïve_srgb	both_naive_sharp
both	prefilt fluor	both_fluor_approx_xyz	both_fluor_approx_srgb	both_fluor_approx_sharp
both	prefilt tung	both_tung_approx_xyz	both_tung_approx_srgb	both_tung_approx_sharp

Certain of the images were not color-balanced properly, but the comparison is still valid.