Global vs local thresholding

I have been facing issues regarding using a particular thresholding tool. The problem starts as soon as I convert my original image into an 8-bit image. Global thresholding which does not require this conversion works pretty fine since it is all based on the original gray values. On the other hand, local thresholding requires conversion into an 8-bit image and for that, I need to adjust the display range of my image. The current display range is pretty much large to get a clear view of the image. So, the thresholding is completely dependent upon how I set the display range?

This all implies that the amount of pores I get is because of the brightness and contrast that I have set to. The only thing I can do is keep the brightness and contrast untouched and just change into 8 bit with the original display range and then change the parameters of local thresholding.
Do you guys have any suggestions on this?
iuppp.tif (8.2 MB)

Check this