are classified into two categories: the parametric
active contour models [6–9] and the geometric active contour
models [10–15]. In this paper, we focus on the parametric active
contour models, and our approach can be also integrated into geometric
active contour models. Since the external force plays a leading
role in driving the active contours to approach objects
boundaries in the parametric active contour models, designing a
novel external force field has been extensively studied [6,8,16–