The bright-chromagenic algorithm for illuminant estimation

In this paper, we propose a new algorithm for illuminant estimation. We begin by reviewing the concept of chromagenic colour constancy, where two pictures are taken from each scene: a normal one and one where a coloured filter is placed in front of the camera, and look at parameters known to affect its performance such as filters and sensor choice. We show that the basic formulation of the chromagenic algorithm has inherent weaknesses: a need for perfectly registered images and occasional large errors in illuminant estimation. Our first contribution is to analyse the algorithm performance with respect to the reflectances present in a scene and demonstrate that fairly bright and desaturated reflectances (e.g., achromatic and pastel colours) provide significantly better chromagenic illuminant estimation. This analysis leads to the bright-chromagenic algorithm. We show that it not only remedies the large error problem but also allows us to relax the image registration constraint. Experiments performed on a variety of synthetic and real data show that the newly designed brightchromagenic algorithm significantly -in a strict statistical senseoutperforms current illuminant estimation methods, including those having a substantially higher complexity.