Normalizing pixel areas in microns of different magnification images taken on a Leica confocal

imagej

#1

How can you normalize the mean gray value of pixel intensities 8 bit (0-255)taken of cells when the images are at different magnifications 400x or 630x with pixels/micron being at 3.723 for some images and 5.882 for other images. I am measuring the mean pixel intensity of each cell (ROI) and the distribution of these means I am using to form a box chart to measure the fluorescence of my peptide within the population of cells