Spatial and temporal discrimination ellipsoids in color space.

Three-dimensional discrimination ellipsoids are presented for a number of representative points in color space. These ellipsoids have been obtained not with the conventional split field but with flickering grating patterns. Thus our study extends the well-known results of Brown and MacAdam [J. Opt. Soc. Am. 39, 808-813 (1949)] to cases in which the image is structured in space and time. As expected, we find that the discrimination ellipsoids depend on the spatiotemporal structure of the stimulus. This has potential consequences for color-difference formulas as used in industry and commerce: no single formula will do when it is important to treat patterns with different structure. We present analytical descriptions, based on the Vos-Walraven [Vision Res. 12, 1327-1365 (1972)] line element augmented with spatiotemporal frequency-dependent coefficients that fit our results reasonably well. For coarse gratings (approximately 1 cycle per degree) or slowly modulated fields (approximately 1 Hz) our results prove to be compatible with the results of Brown and MacAdam obtained with a bipartite 2 degree field.