Watersheds of functions and picture segmentation

The watersheds of a function are geometric features which are very useful in picture segmentation. We briefly and intuitively define the notion of watersheds, and we state that this transformation can be performed starting from the skeleton of the function. This skeleton is a particular case of a general morphological transformation called Thinning. Two examples of use of the watersheds are then given : the first one drawn from contour detection of defects in weld radiographs and the other one from the segmentation of bubbles on an electrophoresis gel.