Video object extraction and shape coding using B-splines

This work presents a system for semi-automatic video object extraction and efficient shape coding using cubic B-splines. In the framework of object-based layered coding of image sequences, shape information is essential for content-based access to video objects, and its efficient encoding needs to be investigated. We present a rate and distortion controlled algorithm for video object shape approximation by variable number of cubic B-spline segments and motion compensated inter-frame coding of B-spline control points. Video object masks are generated using a semi-automatic tracking algorithm. Given an outline of the object in the first frame of the sequence, color and shape models for video object are generated. The adjustment of object´s shape and position in the following frames is based on motion estimation and local color information in the neighborhood of the object´s boundary. Ratedistortion efficiency of the proposed shape coding algorithm is compared to MPEG-4 context arithmetic encoding.