Two Mask-menu entries read a 16-bit TIFF (via ReadTIFFFromString16) and
apply it as the user mask: "replace" overwrites the current mask, "add"
unions the TIFF into it. The TIFF must match the detector dimensions; any
non-zero pixel masks. Both go through UpdateUserMask_i like the other
mask edits.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>