A computer-implemented method is disclosed for recognizing edges in a digital image having a plurality of pixels with gray-scale values defining features. The method includes recognizing edges of the features by cearting a new image in which pixels in the new image corresponding to pixels in the gray-scale image that have a brightness value meeting a predetermined threshold are assigned a first binary value to represent edge regions, while remaining pixels in the new image are assigned a second value to represent both background and internal areas of the features. Area recognition is then performed to distinguish internal feature areas from background areas. The method further includes detecting edge lines from the edge regions that separate features from background and internal feature areas.