Best method to take a difference between 2 images?

I want to take the difference between the following 2 images and then threshold the final output into 2 distinct regions.

However, the problem now is I keep getting image differences that would be hard to threshold/segment because the 2 regions are too similar in value and just look like dark patches (below). I've tried all kinds of image subtraction methods. Please help me out and give me any pointers thank you

Answer 1

[Image Analyst]

Did you try imabsdiff()?