The process is carried out in 2 stages:

• obtaining ``seed points''
• then the ``growing''  step, starting from these points by respecting the characteristics of water surfaces.

The ``seed''points are used as a basis for the growing. It is necessary to be sure that these points belong to the area to be detected. Given that water surfaces appear dark on channel XS3, a good ``seed'' point will be the center of a square whose mean grey level on channel XS3 will be dark.