Colour invariance at a pixel

This paper addresses the question of what can be said about the colours in images that is independent of illumination. We make two main assumptions: Firstly, the illumination can be characterised as Planckian (a realistic assumption for most real scenes). Secondly, the camera behaves as if it were equipped with narrow band sensors (true for a large number of cameras). The resulting physics-based method results in a transformation of the original colour image to a grey-scale one which does not vary with illumination. We give results showing invariance under a range of illumination conditions