The Dichromatic Object Colour Solid

The set of all possible cone excitation triplets from reflecting surfaces tmder a given illuminant forms a volume in cone excitation space known as the object-co/our solid (OCS). An important task in Color Science is to specify the precise geometry of the OCS as defined by its boundary. Schrodinger claimed that the optimal reflectances that map to the boundary of the OCS take on values of 0 or 1 only, with no more than two wavelength transitions. Although this popularly accepted assertion is, by and large, correct and holds under some restricted conditions (e.g., it holds for the CIE colour matching ftmctions), as far as the number of transitions is concented, it has been shown not to hold in general. As a result, the Schrodinger optimal reflectances provide only an approximation to the true OCS. For the case of dichromatic vision, we compare the true and approximate OCS by computing the set of true optimal reflectances, and find that they differ significantly.