Fig. 4.

The principle how additional seed points affect the global segmentation result. Upper Row: some structures in an image, where the goal is to segment the outer boundary (left). Rays are sent out from a user-defined seed point (blue) to prepare the construction of the graph (middle). Nodes for the graph (black dots) are sampled along the rays (right). Lower Row: Segmentation returned the inner boundary (red) due to higher intensity values (left). Two additional seed points (blue) are provided (middle). The additional seeds will return the outer boundary. A result that still includes some parts of the inner boundary (red) is not possible because the additional seeds also affect the neighbor nodes (right)