Active shape models

Abstract

Active shape models encompass a variety of forms, principally snakes, deformable templates and dynamic contours. Snakes are a mechanism for bringing a certain degree of prior knowledge to bear on low-level image interpretation. Rather than expecting desirable properties such as continuity and smoothness to emerge from image data, those properties are imposed from the start. Specifically, an elastic model of a continuous, flexible curve is imposed upon and matched to an image. By varying elastic parameters, the strength of prior assumptions can be controlled. Prior modelling can be made more specific by constructing assemblies of flexible curves in which a set of parameters controls kinematic variables, for instance the sizes of various subparts and the angles of hinges which join them. Such a model is known as a deformable template, and is a powerful mechanism for locating structures in an image.