Perception of illuminant colour changes across real scenes

In a complex natural scene the colour and intensity of the illumination may vary considerably across the scene. Changes in intensity can easily be detected but the same does not seem to be true of colour changes. We investigated the extent to which chromatic changes of the illuminant are detected and the relation of detection performance with colour constancy and scene interpretation. The stimuli were complex real 3-D scenes rendered with spatial colour gradients of which the extremes had correlated colour temperatures within the range 25000 K-3300 K. Observers' sensitivity to these spatial changes of the illuminant was found to be low and critically dependent on scene composition. Also, even in extreme conditions where colour constancy is known to fail, changes in the color of the illuminant across the scenes could not be perceived. These results Suggest that insensitivity to spatial changes of the colour of the illuminant is a strong phenomenon and that it holds regardless of colour constancy.