Boundary-fit to the red channel retinal image: (a) red channel retinal image, (b) green channel counterpart of image in (a), (c) maximum of the image in (a) and its Gaussian blurred image with σ = 24, (d) greyscale-close of the image in (c) with kernel of (10, 10) with all elements unity, (e) part of image in (d) indicated by red boundary of size (300, 300) with initial snake in red on optic disc, ((f), (g), (h), (i), (j), (k), and (l)) active contours after 15, 25, 35, 45, 55, 65, and 75 iterations, respectively, (m) convergence of final snake at 80th iteration on red channel, and (n) boundary of image in (m) shown on green channel image.