1. Watershed Segmentation
Hang Xiao
Jan 25, 2013

2. Idea Region-based segmentation approach
a landscape or topographic relief which is flooded by water
watersheds are the dividing lines of the domains of attraction of rain falling over the region
Basins: local minima
Watershed lines : dams
Mountain ridge
The idea comes from geography that
Basins will fill up with water starting at these local minima, and , at points where water coming from different basins would meet, dams are built.

3. Algorithm (Vincent and Soile)
Generate a list of all pixels in the image in height order.
Pixels belonging to the minimum are labeled with different identifier and placed into a FIFO queue
Loop until all pixels are visited
Removed the top pixel from the queue and put its unvisited neighbors into the queue
For the top pixel label it
if its neighboring have only one kind of labeled identifier, label it with the same identifier
Else label it with watershed line
The fastest and most accurate algorithms base on the flooding analogy. 3 2 1 3 2 1 A B 3 2 W B A 3 B A W B W A
h = 0
h = 1
h = 2
h = 3

4. Example