“…These methods were very sensitive to noise and intensity nonuniformity that can cause discontinuities in the object boundary or induce deviation from the boundary during the tracing process. Efforts have been made to improve robustness by providing a means for crossing discontinuities and by incorporating local intensity information for better edge selectivity [10][11][12][13]. However, local image information alone does not, in general, permit the production of high-quality boundaries.…”