Basic question regarding DIP and Lattice thory

Hi Guys I am new to image processing and Lattice theory. How can i sample an image using my sampling lattice that is [X,Y] = meshgrid(150,150); and my Image is I(x,y)=sin(100*pi*x + 50*pi*y); How one can sample an image in matlab?. It might sound very stupid but i am very new to this field and still learning the basics.

Thanks anyways