Thank you for your reply. I’m sorry I didn’t reply you the other day.
I calculate the mutual information value of Shannon entropy on the image. I believe you have seen it in another question I asked. I calculate it outside the framework. Will this lead to the above situation？（After adjusting the parameters, the similarity measure changes little.）
In addition, I checked the official documents of simpleitk, and found an index I didn’t pay attention to before, which is called “JointHistogramMutualInformation”. Is this the mutual information value of Shannon entropy?
Thank you again for your answer.