Finding RGB image contrast

Question

I want to preprocess images before comparing them. Hence I am making their brightness and contrast same and gray scaling them before comparison. For computing brightness I have used the formula

((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000

Is there any formula by which you can get the contrast value or contrast ratio in an image so that I can set both the images to same contrast before comparing?

Answer 1

Standard methods to match the contrast levels of two or more images are Histogram Equalization and Histogram Matching.