1. A method comprising: performing alpha matting on a multi-dimensional feature set derived from image data of a first image, wherein the multi-dimensional feature set is derived by generating a Frangi image from the first image, applying line filtering to the Frangi image to create a line filtered image and multiplying the line filtered image with the Frangi image; and performing retinal vessel extraction, including performing segmentation on the image by separating foreground and background image data from the first image using an output from the alpha matting.