Hello, I am trying to use the image_threshold function and I noticed that the threshold does not change when scaling the image: iso1=image_threshold(myimage,THRESHOLD=t1,/isodata) iso2=image_threshold(100 * myimage,THRESHOLD=t2,/isodata) I would have expected t2 = 100 * t1, but I get t1=t2. Can anybody explain? Thank you