I want to calculate average luminance of RGB image.
My approach - I am converting RGB image into grayscale image and further taking average all the intensities values of that grayscale.
I am confused about the units of above result. Is it right way to calculate variation of light intensity over images ? Is this is a relative luminance or absolute luminance ?
As grayscale represents light intensity values at every pixels. Hence is it right to say intensity values at pixels will have unity candella/ m^2 ?