how matlab calculate the perimeter of object in binary image

hi

i read this from article

The area can often be accurately estimated by counting the number of pixels inside an object. How- ever, the estimation of the perimeter is a problem, since the length of the original contour might be con- siderably different from the length of the digital con- tour. It is impossible to reconstruct a general con- tinuous contour from discrete data, because many possible contours, all having different lengths, cor- respond to a specific discrete realization

what this mean and how matlab solve it ,which algorithm use>>>???

regards