“…The natural data set contains 25,000 pixels drawn randomly from photographs of animals, plants, and landscapes; the urban data set contains 25,000 pixels drawn from photographs of buildings, streets, traffic, shops, and other urban scenes. Both data sets have a specific distribution, with an abundance of lowly saturated colours and far fewer highly saturated colours (as already observed by Hendley & Hecht 1949). To allow comparison, a third data set containing 25,000 uniformly random sampled Munsell chips is also used.…”