How can I use fuzzy logic to analyze two images in MATLAB?

Question

I have two grayscale images I1 and I2, and three fuzzy rules. The rules are:

1. IF gray value is low in I1 AND gray value is low in I2 THEN case A
2. IF gray value is high in I1 AND gray value is high in I2 THEN case B
3. IF gray value is high in I1 AND gray value is low in I2 THEN case C

Question 1: How can I implement this as a decision based on fuzzy logic?

Now it's the case that I1 follows a clearly bi-modal histogram (so one could easily use a simple threshold to decide in boolean manner between low and high gray values), while I2 follows an almost Rayleigh-shaped, decaying histogram, where a simple threshold is not so easily found (here probably the beauty of fuzzy logic comes into play).

Question 2: How should the membership functions in these cases be designed? And how can they be merged for the final decision, respectively?

Actually, my main interest is to understand the application of fuzzy logic based on this simple example, but in case it helps to use functionality available in MATLAB, this would be an asset.