Two 251x251 images and I want to use as F (x,y)={1 for limit 120 to 130 pixels and 0 for otherwise How do i convert one into function f (x,y).

I have two 251x251 images. For the first image convert it to F(x,y)={1 for 120 <=x <=130 ,0 for otherwise. Second image function: g (x,y)={1 for r <= 5 from the center point x=125 and y=125 ,0 for otherwise. How do i plot and display this images in terms f (x,y) and g (x,y).