Having my first real issue with @GPUOpen's Compressonator. I am passing it a single channel image (R8_Unorm) to convert to BC4, and it keeps coming out black.
Stepped through and it's trying to swizzle the B channel (hint, there is none) into the output image.
Looks like they haven't fixed it yet. I'm unsure what the "correct" fix in their codebase would be, but adding my format (R8) to their "do not swizzle" switch case made it work. The lesson here? Always have source code, friends.