Material and lighting dimensions of object colour.

The dimensionality of the object colour manifold was studied using a multidimensional scaling technique, which allows for the representation of a set of coloured papers as a configuration in a Euclidean space where the distance between papers corresponds to the perceptual dissimilarities between them. When the papers are evenly illuminated they can be arranged as a three-dimensional configuration. This is in line with the generally accepted view that the object colour space is three-dimensional. Yet, we show that under variegated illumination another three dimensions emerge. We call them lighting dimensions of object colour in order to distinguish from the traditional three referred to as material dimensions of object colour.