Dear Ahn,

QuickNII itself supports PNG and JPEG images only, that's why FileBuilder doesn't allow creating series from TIFF images.
A possible ambiguity comes from that QuickNII works in screen-space, showing images in typically 1500*1000 pixels resolution, or only a little bit more. And QuickNII actually needs such images, the underlying runtime can't even load an image above 16 megapixels (say 4000x4000 pixels maximum). So most of the time a downscaling step is required (from original images coming from image acquisition equipment, to something screen-sized).
While the analytical tools, like Nutil, can and usually do work with much larger images, often several gigapixels in size, like 150000x100000 pixels, and such images are often easier to handle as TIFF, because it supports tiling for example.
Practically in our laboratory we maintain two sets of images for these workflows, one set of low-resolution images for QuickNII (and https://www.nitrc.org/projects/visualign/), and the actual original images for analysis.

Best regards,
Gergely