The technique of Fast Watershed is called immersion, and it is based on a simulation of the rise of water from a set of markers. The level p is flooded at a
uniform speed from the fronts coming from level p-1 and the local minima appear at level p. A point of the watershed appears when two distinct fronts join.
Figure 1:
The Fast Watershed principle
Figure 2:
Example of how the result depends on the choice of markers
