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Divergence-aided gradient vector flow snakes

Gradient Vector Flow (GVF) is an important external force field driving active contours evolution. However, due to difficulties in evolving over the saddle and stationary points of the GVF field, the GVF snake which takes the GVF field as the external driving force suffers from a poor performance of dealing with complex geometries. In this paper, using the divergence of GVF field we construct a new balloon force which can determine the curve evolution when the GVF force is not valid. The modified GVF snakes model with the balloon force has a better capability of dealing with complex geometries. The significant difference between the proposed and existing balloon forces (e.g. constant force) is that the proposed divergence based balloon force has a negative value on the edge of image and so can better prevent the occurrence of boundary leakage. Some experiments on synthetic and real images are presented in this paper.