About GLCM min&max

I used SNAP to perform GLCM processing on SAR images. And I want to normalize these images for neural network training. I used Python to find the maximum and minimum values ​​of these images, but these values ​​are somewhat different from my estimation(From the perspective of probability, should the maximum and minimum be between 0 and 1?).
So how should I obtain the formula used by SNAP in the process of GLCM calculation, or the theoretical maximum and minimum values?

Thank you!!!