I have a merged image stack (from two composite stacks), with a screenshot of a slice shown here. This was done in ImageJ. Essentially, the water (blue) was injected into a gas diffusion layer (i.e., a porous material made primarily of carbon fiber). The black regions are air. How can I take that merged stack and create a new image stack of only the black region in ImageJ?
To put things in context, I'm eventually going to take the three different stacks (gas diffusion layer, water, air), create meshes from them, and find where the three all intersect (i.e., the triple-phase contact line). After some smoothing, I'll then calculate vertex normals along all the contact lines to calculate average contact angles of water in the gas diffusion layer.