How To Estimate Brightness-Contrast Value of Gray Figure?

Question

Situation: I have gray figures, figure A and figure B, where figure B is wider than figure A; Figure B is very light although from the same situation but with little more perspective/view/data in it; I cannot estimate what is the point of figure B in the brightness-contrast plane
Characteristic: my pictures become very light when I take wide pictures; I do not understand what can cause it

I have Gimp/ImageMagick/... in my system. I would like to have both figures with the same value in the brightness-contrast plane.

System: Debian 8.5 64 bit, Ubuntu 16.04 64 bit
Linux kernel: 4.6 of backports

Answer 1

I don't think you can see this in terms of brightness/contrast, what you can do is

1. using Levels, make sure that the histograms of both images have the same span (one may not have blacks or whites)
2. find places in one image that are roughly on grays 25%-50%-75%
3. find equivalent places in the other image, and use Curves to adjust their values (a bit like what is done here)