Measuring Colour Constancy and Colour Appearance: an Experiment

Colour sensation does not depend strictly on the light signal conveying colour information, but also depends on the arrangement of the visual array of all signals coming from the scene. Colour constancy is one aspect that contributes to the Human Vision System (HVS) in the formation of colour appearance. In the digital-imaging field the concept of colour constancy is often related with a process of trying to identify the object’s reflectance from the light that comes from it. That light is the product of reflectance and illumination. One could separate the reflectance component from the illuminant component, by discounting the illuminant [1]. Although this is claimed to be a useful operation for several applications in computer vision, it is not an accurate description of our human colour appearance mechanism. Human vision, in fact, does not separate the two components and does not completely eliminate either of the two. HVS developed the ability of normalizing scene appearance across the variation of illuminant and spatial object configuration. In doing this, it is affected not only by the reflectance of the object in the scene and by the spectral content of the illuminants, but also by the spatial array of reflectances and by the spatial non-uniformity of illumination.