What is the need of calculating mean,variance for an image

What is the need of calculating mean,variance for an image

[Rik]

That will depend entirely on your application.

Answer 1

[Jan]

Mean and variance of what? The R, G and B channels of a color image? Or of the intensities of gray channels? This can be needed e.g. for comparing a set of images, determining the sharpness or information density. There is a variety of applications, so asking for the "need" is hard to answer. What is the need of the mean and the variance in statistics?