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Carlos A Parraga, Tom Troscianko, Jolyon Troscianko, David J Tolhurst, Ute Leonards; Spatiochromatic properties of images of fruits and leaves from Kibale forest, Uganda. Journal of Vision 2003;3(9):315. doi: 10.1167/3.9.315.
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© ARVO (1962-2015); The Authors (2016-present)
The human visual system (hvs), as well as that of other trichromatic primates, has different contrast sensitivity functions for chromatic and luminance stimuli. The spatial filtering is low-pass for chromatic stimuli and band-pass for luminance. Previous results have shown that a subset of natural scenes, namely those with red objects (e.g.fruit) on a background of leaves have spatial properties that correspond to this physiological spatial filtering (Parraga, Troscianko and Tolhurst; Current Biology 12, 483–487; 2000). Our original dataset on which these conclusions were based was consisted of English natural scenes. Here we analysed the spatiochromatic properties of a dataset of natural scenes obtained in Kibale Forest, Uganda, which is a natural habitat containing large numbers of wild trichromatic primates. We used the same calibrated digital camera as in the previous study, which delivers L,M,S cone responses, and opponent-channel responses, for each pixel. We obtained 270 images of scenes, many of them containing red fruit, red leaves, red flowers and green leaves corresponding to the primate visual environment as seen from the ground and from the canopy. All the red fruit and leaves were confirmed as forming a significant part of the diet of trichromatic primates. Our results support the earlier finding (with English plants), namely that the luminance and chromatic Fourier spectra of pictures containing reddish objects on a background of leaves correspond well to the spatio-chromatic properties of the luminance and red-green systems in human vision, at viewing distances of the same order of magnitude as the grasping distance.
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