Acquisition and Analysis of Bispectral Bidirectional Reflectance and Reradiation Distribution Functions

摘要

In fluorescent materials, light from a certain band of incident wavelengthsrnis reradiated at longer wavelengths, i.e., with a reducedrnper-photon energy. While fluorescent materials are common in everydayrnlife, they have received little attention in computer graphics.rnEspecially, no bidirectional reradiation measurements of fluorescentrnmaterials have been available so far. In this paper, wernextend the well-known concept of the bidirectional reflectance distributionrnfunction (BRDF) to account for energy transfer betweenrnwavelengths, resulting in a Bispectral Bidirectional Reflectancernand Reradiation Distribution Function (bispectral BRRDF). Usingrna bidirectional and bispectral measurement setup, we acquire reflectancernand reradiation data of a variety of fluorescent materials,rnincluding vehicle paints, paper and fabric, and compare their renderingsrnwith RGB, RGB×RGB, and spectral BRDFs. Our acquisitionrnis guided by a principal component analysis on complete bispectralrndata taken under a sparse set of angles. We show that in order tornfaithfully reproduce the full bispectral information for all other angles,rnonly a very small number of wavelength pairs needs to bernmeasured at a high angular resolution.