What Color is the Sky (for a non-human) ?
For vision scientists and biologists, this work provides a tool to estimate color perception in non-human animals, though it is an incremental extension of metamerism concepts.
The paper presents a computational method to find monochromatic metamers of skylight for arbitrary visual systems, showing that the perceived color of the sky varies drastically across species (e.g., bichromats, trichromats, tetrachromats) and can be very different from human blue.
The light of the daytime sky contains a mixture of many colors yet is perceived as blue by human observers. This is largely due to the particular response functions of the human cones. Under these response functions skylight and blue light are metamers: they yield the exact same excitation of the cones. In this paper we ask: is it possible to define the ``color'' of the sky for other visual systems? We present a simple computational method to determine monochromatic metamers to a given input light for arbitrary visual systems. Using published values on spectral sensitivity functions of various species, we use our method to determine the dominant wavelength of monochromatic metamers to skylight. For a wide range of species (bichromats, trichromats and tetrachormats) we find monochromatic metamers to skylight but the dominant wavelength of the metamer can vary drastically between species and be very different from the color perceived by humans.