Active shape focusing

This paper presents a framework for hierarchical shape description which en ables quantitative and qualitative shape studies at multiple levels of imag e detail. It allows the capture of the global object shape at higher image scales, and to focus it down to finer details at decreasing levels of image scale. A multi-scale active contour model, whose energy function is regula rized with respect to underlying geometric image structure in a natural sca le setting, is developed for the purpose of implicit shape extraction or re gularization with respect to scale. The resulting set of shapes is formulat ed and visualized as a multi-scale shape stack for the investigation of sha pe changes across scales. We demonstrate the functionality of this framewor k by applying it to a set of true fractal structures, and to 3D brain MRI. The framework is shown to be capable of recovering the fractal dimension of the fractal shapes directly from their embedding image context. The equiva lent measure on the medical images and its potential for medical shape anal ysis is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.