Cite as:
Oxtoby E K, Foster D H, Amano K, Nascimento S M C, 2002, "How many basis functions are needed to reproduce coloured patterns under illuminant changes?" Perception 31 ECVP Abstract Supplement

How many basis functions are needed to reproduce coloured patterns under illuminant changes?

E K Oxtoby, D H Foster, K Amano, S M C Nascimento

Some approaches to surface-colour perception assume that spectral reflectances may be mathematically well represented by low-dimensional linear models. In practice, however, principal component analyses of natural scenes illuminated by daylight suggest that observers need about six basis functions to represent adequately surface reflectance spectra [Nascimento et al, 2001 Investigative Ophthalmology & Visual Science 42(4) 3871]. This requirement might be relaxed if representations were required only to appear invariant under illuminant changes. To test this hypothesis, observers were presented with computer simulations of pairs of Mondrian-like coloured patterns comprising 49 (7 × 7) abutting 1 deg × 1 deg square Munsell papers; in half of the trials, the spectral reflectances of the surfaces were replaced by an approximation comprising a variable number of basis functions; observers had to report whether the two patterns were of the same materials. In one condition the patterns appeared under identical daylights of correlated colour temperature 6700 K and in another condition under two different daylights with correlated colour temperatures of 25 000 K and 6700 K. Under both identical and different illuminants, most observers required at least five basis functions for the discrimination of the patterns to be at chance, suggesting that low-dimensional linear models provide insufficient colour representation in this context.

[Supported by EPSRC.]

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