The tie-zone watershed: definition, algorithm and applications

In this work, a new type of watershed transform is introduced: the tie-zone watershed (TZWS). This region-based watershed transform does not depend on arbitrary implementation and provides a unique and optimal solution. Indeed, many solutions are sometimes possible when segmenting an image with a watershed algorithm. In this case, the TZWS assigns each pixel to a catchment basin (CB) if in all solutions it belongs to this CB. Otherwise, the pixel is said to belong to a tie-zone (TZ). We propose an efficient algorithm based on image foresting transform (IFT) which computes the TZWS transform as a shortest-path forest. Finally, two applications of this TZWS are presented: bounding intervals for segmented objects' extensions and a progressive segmentation procedure.