For instance with 8-bit greyscale images, the intensity range is from 0-256. I would need to be able to first calculate the average intensities of each image. This is the real part of the problem. If one image's intensity is 125 and the other is 180, how would I be able to get these numbers through MATLAB? Once I have them it is a simple calculation of 125/180 to find the proportion I'm looking for, but how do I even get to this step?

On a related note, I would also like to know how to have a greyscale image return a greyscale histogram instead of a color one...

For any of you curious as to why I would need to have this image comparison - it has to do with Beer's Law in chemistry for calculating concentrations of a solution by measuring absorbance of a solution using optical equipment.

Thanks!