A coarsely estimated object boundary is formed by a sequence of edge boundary points. A local affine transformation along the estimated object boundary is identified by analyzing edge energy of a current image frame. A sequence of edge boundary points which have edge energy change ratios exceeding a threshold value is identified as a local affine transformation. A refined estimate of the object boundary is determined for the local affine transformation using a local segmentation process based on a key contour point search strategy. End points of the contour are assumed to be known. An initial key contour point is derived from the coarsely estimate object boundary. Candidate key points then are derived and corresponding curves analyzed to select a curve as the improved estimated boundary for the local affine transformation. The curve having a minimum average edge energy change ratio is selected.