When working with registered and aligned images that are of different size, I use imagemagick to frame the 16 bit tiff files, with this little script:

#!/bin/bash
OUTPUTRES="4300x2900"
mkdir output
for filename in *.TIF*; do
     convert "$filename" -background black -gravity center -extent $OUTPUTRES output/"$filename".out.tif
done

for filename in *.tif*; do
     convert "$filename" -background black -gravity center -extent $OUTPUTRES output/"$filename".out.tif
done