You can't. And if you use pcolor, you don't either. The tiles you see in pcolor are NOT pixels. Look closely. If you want to show a 4x4 array with pcolor, do you see a 4x4 array of pixels?
m = magic(4)
No, you don't. Those black lines goes through the MIDDLE of the pixels, they don't surround them. And to make it worse, you see a 3x3 array of tiles, not a 4x4 array. Very deceiving so that's why I never use pcolor().