Adaptive balloon models

The original snake models require a close initialization which in many situations are difficult to acquire. The balloon model presented by Cohen et al. to solve this problem suffers from the difficulty of choosing a constant inflating force due to variable internal shrinking forces and non-constant boundary intensity levels. Xu et al., on the other hand, proposed to use a pressure force to exactly offset the shrinking forces. The resulting model achieves better stability in terms of parameter insensitivity by sacrificing smoothness constraints, thus it would go through even small gaps on a boundary. We instead propose to compute an adaptive inflating force locally for each snaxel so that it is just enough to overcome the image force. A new smoothness constraint which can maintain smoothness without any shrinking side-effects is also presented, along with a new way to resample a balloon without significantly reducing its tension. The combined model is sensitive to weak and incomplete boundaries, and yet able to overcome noise edges. Experimental results are reported to support our statements