I abandoned PIL/Pillow a couple of years ago for OpenCV (a lot faster, and loads 16/32 bit int/float TIFs without problems), but I remember there were a couple

I abandoned PIL/Pillow a couple of years ago for OpenCV (a lot faster, and loads 16/32 bit int/float TIFs without problems), but I remember there were a couple of "utility functions" whose job was to translate from PIL.Image into a numpy.ndarray and back. I guess you'd convert every frame from the corresponding ndarray, and then save them into a list to build the GIF in memory.