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Thesis (PDF) - Signal & Image Processing Lab

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80 CHAPTER 6. EXTREMA-WATERSHED TREE EXAMPLE<br />

Figure 6.3: The Extrema Watershed Tree associated to the example in Fig. 6.2.<br />

Algorithm 3 Create maxima watershed tree<br />

A list of symbols :<br />

Eq A sorted queue of edges in G containing extremum region.<br />

Ngh A sorted queue of edges, a subset of Eq, neighbors of Vextr, V2.<br />

Lbl The current label number, initialized to zero.<br />

1: Find all extremum region ,Vextr, in G.<br />

2: Find all edges connected to the extremum regions and put them in Eq.<br />

3: Sort Eq according to the comparison function in alg. 2.<br />

4: while Eq not empty do<br />

5: (Vextr, V2) ← F irst(Eq)<br />

6: Lbl = Lbl + 1<br />

7: Create new vertex V<br />

8: Lbl(V ) ← Lbl<br />

9: GL(V ) ← GL(V2) ⊲ The new vertex always gets GL other then extremum<br />

10: Size(V ) ← Size(Vextr) + Size(V2)<br />

11: F ather(Vextr) ← V ; F ather(V2) ← V<br />

12: Ngh ← all pairs in Eq containing Vextr or V2<br />

13: Substitute Vextr and V2 by V in Ngh.<br />

14: Remove all pairs in Ngh where the first vertex is not extremum anymore.<br />

15: Sort Ngh according to the comparison function in alg. 2.<br />

16: Merge Eq and Ngh preserving the order.<br />

17: end while<br />

18: Root ← Lbl ⊲ the last added label is defined as the root

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