Abstract: Snake models compromises low-level knowledge of images and the high-level knowledge of
images. Snake models have been widely used in target tracking, edge detection, image segment and
reverse engineering. It is considered as an active research field. Clear mechanic theory is included in
Traditional snake models and some improved active contour models. The mechanic theory of traditional
snake models and the B-snake models which is based on the theory of B-spline is presented firstly.
Because of some defects in traditional snake model, some improved active contour models also are
discussed from the mechanics view. In additional, the convergence process of the snake models and the
active contour with inertia force are interpreted by Lagrange dynamics. In the end, the summary and the
expectation are proposed.

Key words: active contour models, mechanic theory, computer vision, B-spline curve, GVF model