2 D Shape Estimation for Moving Objects

The estimation of the 2D shape of moving objects in a video image sequence is required for many applications, e.g. for so-called content-based functionalities of ISO/MPEG-4, for object-based coding, and for automatic surveillance. Many real sequences are taken by a moving camera and show moving objects as well as their cast shadows. In this paper, an algorithm for 2D shape estimation for moving objects is presented that considers for rst time explicitly both, a moving camera and moving cast shadows. The algorithm consists of ve steps: Estimation and compensation of possibly apparent camera motion, detection of possibly apparent scene cuts, generation of a binary mask by detection of temporal signal changes after camera motion compensation, elimination of mask regions corresponding to moving cast shadows and uncovered background, and nally, adaptation of the mask to luminance edges of the current frame. For identiication of moving cast shadows, three criteria evaluate static background edges, uniform change of illumination, and shadow penumbra. The proposed algorithm yields accurate segmentation results for sequences taken by a static or moving camera, in absence and in presence of moving cast shadows. Parts of this algorithm have been accepted for the informative part of the description of the forthcoming international standard ISO/MPEG-4.