Colour normalisation and spatial comparison : a robust way to integrate the light spectrum

In the physical world no colours exist, only light energy distributions with various spectral compositions. It is well known that there is a direct relationship between the spectral power distribution and the perceived colour when the colour is considered out of context. If a colour is perceived in context, this relationship no longer holds. To integrate the rich amount of spectral information, in order to obtain the triplet necessary to generate colour sensation, the human retina integrates the spectrum by means of the cone sensitivity curves. Colorimetry does the same using colour matching functions. Considering colour out of context, small changes in the integration curves result in corresponding changes in colour. In the case of colour in context this does not apply, since human vision colour normalisation mechanisms play an important role. This paper presents experiments that show how colour normalisation and spatial computation can compensate changes in the integration curves. In other words, the human visual system has developed ways to adjust to changing lighting composition and distribution. Experiments prove that these mechanisms can also compensate differences in cone sensitivities, or more generally in every set of spectrum integration curves.