how to get the area under the "inpolygon" regions in an image

I have used the "inpolygon" function to divide my image into four parts. and i want to calculate the area of the image inside each rectangle and obtain the polygon with containing the highest area of the image.

[KSSV]

When you have used inpolygon, to divide the image, you should be having the coordinates in your hand, it makes you to calculate the area easily. Show us the image.