Space-average scene colour used to extract illuminant information

Human observers are able to determine whether changes in the colour appearance of a complex scene are consistent with a change in the spectral composition of the illuminating light or of the reflecting properties of its constituent materials (Craven and Foster, 1992; Foster et al., 1992). When an illuminant change is sufficiently large, it is perceived as a change in the space-average colour of the scene; in other words, it appears as though a wash of a different colour had been applied uniformly across the scene. The two experiments reported here were designed to investigate the capacity of human observers both to extract information about space-average colour and to use it to provide information about illuminant colour.