Frequency of mismatching surface colors in the wild.

Colored surfaces may appear to match in one viewing condition but not in another, usually because of a change in illumination. The aim of this computational study was to estimate the frequency of mismatching outdoors under natural, uncontrolled, illumination changes, unlike the purely spectral changes in studies of illuminant metamerism. Data were taken from hyperspectral radiance images acquired at intervals of 1 min to more than 4 h. For pairs of randomly chosen surfaces in a scene, the relative frequency of their appearing initially the same and different later was around 10^-4 to 10^-3, depending on color difference. However, if they already appeared the same, the relative frequency was higher, around 6% to over 60%, much higher than for illuminant metamerism, suggesting that real-world lighting changes may well impair surface identification by color.