  The color sensation evoked by an object depends on both the spectral power
distribution of the illumination and the reflectance properties of the object
being illuminated. The color sensation can be characterized by three
color-space values, such as XYZ, RGB, HSV, L*a*b*, etc. It is straightforward
to compute the three values given the illuminant and reflectance curves. The
converse process of computing a reflectance curve given the color-space values
and the illuminant is complicated by the fact that an infinite number of
different reflectance curves can give rise to a single set of color-space
values (metamerism). This paper presents five algorithms for generating a
reflectance curve from a specified sRGB triplet, written for a general
audience. The algorithms are designed to generate reflectance curves that are
similar to those found with naturally occurring colored objects. The computed
reflectance curves are compared to a database of thousands of reflectance
curves measured from paints and pigments available both commercially and in
nature, and the similarity is quantified. One particularly useful application
of these algorithms is in the field of computer graphics, where modeling color
transformations sometimes requires wavelength-specific information, such as
when modeling subtractive color mixture.
