1. A computer-implemented method of segmenting a digitized image comprising the steps of: providing a digitized image comprising a plurality of intensities corresponding to a domain of points on an N×N grid wherein N is a positive integer; defining a weight between each pair of adjacent points in the image based on the intensity difference of each said point pair; marking a subset of points in the image; associating a probability potential with each unmarked point; and using a multigrid method and a computer to solve for the probability potentials for each unmarked point, wherein a restriction operator for the image is applied to an (N−1)×(N−1) image wherein each said weight in the image is associated with an adjoining point to define a weight for applying said restriction operator, wherein said restriction operator determines weights of a coarse level grid.