title: Open problems in color constancy: discussion.
abstract: This paper discusses a number of open problems in color constancy theory whose correct solution is a prerequisite for the theory of the phenomenon. Solutions employing suitable visually meaningful versus physically meaningful basis functions (principal components) are examined. In the former case the starting point is an estimate of the first derivative of the reflectance (illuminant), essential for defining color, instead of an estimate of the reflectance (illuminant), as in the latter. Conceptual consequences are discussed. Mathematical and physical constraints are identified. We compare the results of theories that do or do not ignore them. The following questions are considered. (1) Do unique solutions of the estimation problem exist everywhere in the object-color solid belonging to the illuminant? (2) Are they physically meaningful, i.e., at least nonnegative? (3) Are they representative for reflectance and spectral distribution functions? (4) What role plays metamerism?
authors.forename: C
authors.initials: C
authors.lastname: van Trigt