A Direct Test Of The 'Grey World Hypothesis'; A Comparison Of Different Matching Methods

Many of the proposed ways in which the visual system could disentangle influences of illumination from influences of reflection on the colour of the light that reaches our eyes, are implicitly or explicitly based on the assumption that the average reflectance of our environment is grey; the 'Grey World Hypothesis'. Here we investigate whether subjects make large errors when this assumption is not true. Subjects performed matching tasks in which they matched the colour and luminance of a test plate, either by setting the colour o f an adjustable patch on a monitor or by selecting a sample from a large set of printed colour samples '(Pantone Colour Specifier)'. Matches were made with the test plates embedded in scenes either containing only red or only green objects. Matches hardly differed between the red and green scenes. Thus, the average colour of the scene cannot be the primary scene statistic underlying colour constancy. We found that the matches were most consistent both across and within subjects when using the Pantone Specifier.