Figure 2. Flat-matte-diffuse conditions.

A collection of flat, matte surfaces is illuminated by a diffuse light source with spectral power distribution E(λ). The color signal C^j(λ) reflected from the j^th surface is given by C^j(λ) = E(λ)S^j (λ), where S^j (&laambda;) is the surface reflectance function of that surface. The cone excitation vector elicited by C^j (λ) is ρ^j The set of ρ^j, across the retinal image, {ρ¹,…,ρⁿ}, is the information available to computational algorithms that seek to estimate illuminant and surface properties under flat-matte-diffuse conditions. It is also the information available to the human visual system for producing the perceptual representation that is color appearance. When we consider the properties (either physical or perceptual) of a specific surface (denoted the j^th surface), we often refer to it as the test surface and refer to the collection of surfaces making up the rest of the scene together with the illuminant as the scene context.