Segmenting film sequences using active surfaces

Special effects in motion pictures largely employ image compositing to seamlessly join picture elements together from separate sequences. The extraction of objects such as actors from real backgrounds rather than blue screens requires manual tracking of the object boundary by skilled operators: an inaccurate and error-prone task which inevitably generates a bubbling artifact. An active surface model defined over the three dimensional spatio-temporal space is recovered whose intersection with each image plane represents the required object boundary. Such active surfaces are a generalisation of snake contours common in many image processing applications. Initial crude boundaries are drawn in end frames and key intermediate frames to construct an initial surface. A energy minimisation process is used to iteratively refine the location of boundaries in all frames simultaneously. User selected edge data may also be employed to guide the crudely specified initial contours to their correct location.