Acquiring and prepping images

Pseudogymnoascus destructans is a psychrophilic fungus that can infect bats during hibernation. By transilluminating with long-wave ultraviolet (UV) light (366-385 nm), the fungus emits a distinct orange-yellow fluorescence that corresponds directly with the fungal cupping erosions.

The image above was taken by briefly holding a bat over a long-wave UV light that emits the 366-385 nm wavelengths known to incite the characteristic orange—yellow fluorescence. The countcolors package will be able to calculate the area of the wing affected with this fluorescence once the background is masked. To do this we need to make sure that only the wing membrane is visible and the background is a single, uniform color, that is as dissimilar to the wing-membrane and orange—yellow fluorescence as possible. This background color will be ignored by countcolors and so only the area of the wing membrane will be used in the calculations.

We used Photoshop 2018 to select the wing membrane, however you can use any image editing software that allows you to create a single, uniform background color. Additionally, we never manipulated any original photos, so create a copy of each image you want to alter and work only with the copy.

Because GIMP is an openware software and freely accessible, we have provided directions for isolating the wing in the above photograph. Open the copy of our above bat wing photo using GIMP. From the tool bar, select Layer \(\rightarrow\) Transparency \(\rightarrow\) Add alpha channel.