Image processing
We used the MICA toolbox in ImageJ v1.52k to linearize, align, and
combine our paired VIS and UV photographs into a series of multispectral
images (Schneider et al. 2012; Troscianko and Stevens 2015). We used the
10% and 77% reflectance standards to linearize the images, and each of
the photo pairs were aligned manually. We then manually selected regions
of interest (ROIs), from each multispectral image, by selecting up to
six of the strongest UV reflecting regions (UV+), and up to six
similarly sized and shaped adjacent regions that did not reflect UV
(UV-).
For the butterflies, we selected ROIs from the undersides of both the
forewings and hindwings as these regions will be visible to both
predators and conspecifics, and where most species had the greatest UV
reflectance. In the frogs, the location of the UV reflecting regions was
more variable but was limited to dorsal, lateral and inguinal regions
which would similarly be visible to avian predators. All ROIs were also
chosen to avoid regions of specular reflectance (see Figure 1 for
species-specific UV reflection regions).