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We have generated a new dataset of digital natural images where each colour plane corresponds to the human LMS (long, medium, shortwavelength) cone activations. The images were chosen to represent five different visual environments (eg forest, seaside, mountain snow, urban, motorways) and were taken under natural illumination at different times of the day. At the bottom-left corner of each picture there was a matte grey ball of approximately constant spectral reflectance (across the camera’s response spectrum,) and nearly Lambertian reflective properties, which allows to compute (and remove, if necessary) the illuminant’s colour and intensity. The camera (Sigma Foveon SD10) was calibrated by measuring its sensor’s spectral responses using a set of 31 spectrally narrowband interference filters. This allowed us to convert the final camera-dependent RGB colour space into the Smith and Pokorny (1975 …