My images don't appear in the General Registration Module (BRAINS)

Title pretty much explains it all. But I am uploading two tiff files to register and was hoping to utilize the general registration module. When I go to choose fixed and moving image volumes, the options for my loaded files do not appear. I can still view the images in other modules like transform and volume but I’m confused as to why they aren’t loading into this specific module.

Version 4.11.20200930 r29402 / 002be18 on the Mac

BRAINS (and most other image registration tools) work on grayscale images. You can convert your image to grayscale using “Vector to scalar volume” module. See documentation for some more details.