Fig. 4. In situ reflectance measurements of brightly coloured crabs recorded using a spectrographic imager (CASI) (A) and a UV-sensitive camera (B). Imager and camera viewed a fiddler crab colony from a height of about 1 m at an angle of 45° with an angular resolution of 0.025°. Example scans are shown on top for the spectrographic imager and below for the UV-sensitive camera. (A) Average reflectance spectra with their standard deviation (shaded) for three female crabs numbered 1–3 in the spectrographic imager scan: blue: blue-white patches on carapace; black: mudflat background. Inset pictures show, for crab 1, how areas of interest were selected (left: original image, right: regions of interest with blue carapace marked blue and mud flat background marked black). For details see Materials and methods. (B) UV images together with their 2D density functions.