Recording animal-view videos of the natural world using a novel camera system and software package
Fig 2
Frame excerpts from false color videos.
Our pipeline can produce false color videos of animals behaving in their natural environment. (A) Here, we show 3 male orange sulphurs (Colias eurytheme). These butterflies display strong angle-dependent UV iridescence on the dorsal side of their wings. The UV-iridescent portions appear more orange to the human observer than the otherwise yellow wings (see human-visible inset). The avian false color depiction (main image) is based on the coordinates of the receptor noise-limited (RNL) opponent space [17,44]. Coordinates in this space represent differences in an animal’s photoreceptor responses, and the distances between the coordinates approximate the perceptual distances between the colors. The inset color key illustrates human-visible colors around the perimeter of a circle colored according to RNL coordinates, where UV colors start at the epicenter and mix with other colors. For full details, see Method A in S1 Text. In this depiction, the UV-iridescent portions appear purple, because they most strongly reflect in the ultraviolet and the red part of the spectrum. The ventral part of the wings, visible when the animals are in their resting position, are depicted as gray-brown, just like the leaves, as they are close to the achromatic point. See S1 Video. (B, C) A potentially useful application of the system is the fast digitization of museum specimens. Here, we highlight pigmentary and structural UV coloration on specimens of (B) Phoebis philea and (C) Anteos sp. in RNL false colors. A human-visible inset appears to the top right corner of each. The specimens are mounted on a slowly rotating stand, showcasing how the iridescent colors change depending on viewing angle (S2 and S3 Videos). The bright magenta colors highlight the strongly UV-reflective areas, while the purple areas reflect similar amounts of UV and long wavelength light. For the purpose of this illustration, we applied a gamma correction to the false color video of the (A) live butterflies; the source videos are also available. For further examples, see S4–S12 Videos.