The Effect of the Field of Adaptation on Chromatic Discrimination Ellipses

In this paper results of chromatic discrimination measurements obtained in two lighting scenarios are compared. Chromatic discrimination thresholds were measured in relation with systematically manipulated chromaticities seen under different visual angles. In both cases the Ellipse module of the Cambridge Colour Test (CCT) was obtained binocularly by normal colour-observers. Discrimination ellipses fitted to the measured thresholds were compared in terms of the adapting chromaticity and the visual angle of the adapting stimulus. Our findings show that changes in the reference chromaticity of the CCT have stronger effect on the elongation of the chromatic discrimination ellipses compared to the effect of the adapting chromaticity obtained in a light booth. Further comparison of discrimination thresholds estimated towards the confusion directions and the corresponding radii of the Ellipse test results suggests that the reliability of the Ellipse test results depends on the relation between the measurement directions and the confusion directions.