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Abstract:
In fluorescent materials, energy from a certain band of incident wavelengths is
reflected or reradiated at larger wavelengths, i.e. with lower energy per
photon. While fluorescent materials are common in everyday life, they have
received little attention in computer graphics. Especially, no bidirectional
reflectance measurements of fluorescent materials have been available so far. In
this paper, we develop the concept of a bispectral BRDF, which extends the
well-known concept of the bidirectional reflectance distribution function (BRDF)
to account for energy transfer between wavelengths. Using a bidirectional and
bispectral measurement setup, we acquire reflectance data of a variety of
fluorescent materials, including vehicle paints, paper and fabric. We show
bispectral renderings of the measured data and compare them with reduced
versions of the bispectral BRDF, including the traditional RGB vector valued
BRDF. Principal component analysis of the measured data reveals that for some
materials the fluorescent reradiation spectrum changes considerably over the
range of directions. We further show that bispectral BRDFs can be efficiently
acquired using an acquisition strategy based on principal components.
