An Implicit Active Contour Model for Feature Regions and Lines

We present a level-set based implicit active contour method which can detect innermost homogeneous regions which are often considered feature regions or lines depending on the width of the regions. The curve evolution algorithm is derived from optimization of energy defined for the evolving curves. The energy has basically three terms: the first is the energy of the regions inside the curves, the second the energy of the bands inside the curves, and the third the energy of the bands outside the curves. If the band width is small, the total energy is minimized when the evolving curves lie at the boundaries of the innermost homogeneous regions, and the regions inside the curves are considered feature regions. Our method contrasts with the Chan-Vese model, which does not have the notion of innermost homogeneous regions but tries to find the curves such that the regions inside and outside them are both homogeneous. Our model approaches Chan-Vese model as the band width is increased, and is equivalent to Chan-Vese model when the band width is sufficiently large, so that all points inside/outside the curves lie within the bands inside/outside the curves, respectively.