Marker-based watershed example
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(shaded pixels are on frontier) |
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8 |
7 |
5 |
4 |
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2 |
0: (1,3) |
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9 |
6 |
2 |
1 |
1: (3,1), (2,3), (1,4), (4,4) |
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4 |
2 |
7 |
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4 |
2: (2,1), (4,1), (1,2), (4,3) |
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0 |
1 |
8 |
2 |
3: (4,0), (3,2), (0,3), (2,4) |
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6 |
4: (3,0), (0,2), (4,2) |
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1 |
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6 |
1 |
5: (2,0) |
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gradmag image |
6: (1,1), (0,4), (3,4) |
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u u u u 1 |
7: (1,0), (2,2) |
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u u 1 |
1 |
1 |
8: (0,0), (3,3) |
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9: (0,1) |
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u 0 u |
1 |
1 |
Step 10: k=3 |
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pixel list |
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0 |
0 |
0 |
u 1 |
Grow catchment basins |
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u 0 0 |
u 1 |
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labels
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847
Marker-based watershed example
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(shaded pixels are on frontier) |
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8 |
7 |
5 |
4 |
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2 |
0: (1,3) |
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9 |
6 |
2 |
1 |
1: (3,1), (2,3), (1,4), (4,4) |
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4 |
2 |
7 |
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4 |
2: (2,1), (4,1), (1,2), (4,3) |
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0 |
1 |
8 |
2 |
3: (4,0), (3,2), (0,3), (2,4) |
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6 |
4: (3,0), (0,2), (4,2) |
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1 |
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6 |
1 |
5: (2,0) |
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gradmag image |
6: (1,1), (0,4), (3,4) |
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u u u u 1 |
7: (1,0), (2,2) |
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u u 1 |
1 |
1 |
8: (0,0), (3,3) |
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9: (0,1) |
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u 0 u |
1 |
1 |
Step 11: k=3 |
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pixel list |
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0 |
0 |
0 |
u 1 |
Expand frontier |
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u 0 0 |
u 1 |
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(nowhere to expand) |
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labels
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847
Fast forward…
Marker-based watershed example
8 7 5 4 3
9 6 2 1 2
4 2 7 3 4
3 0 1 8 2
6 1 3 6 1
gradmag image
0 0 1 1 1
0 0 1 1 1
0 0 0 1 1
0 0 0 0 1
0 0 0 0 1
0:(1,3)
1:(3,1), (2,3), (1,4), (4,4)
2:(2,1), (4,1), (1,2), (4,3)
3:(4,0), (3,2), (0,3), (2,4)
4:(3,0), (0,2), (4,2)
5:(2,0)
6:(1,1), (0,4), (3,4)
7:(1,0), (2,2)
8:(0,0), (3,3)
9:(0,1)
pixel list Final result
(but note that ties can be broken in other ways)
labels
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847
Marker-based watershed
threshold |
chamfer |
watershed |
edges |
image
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or |
gradient |
markers |
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magnitude |
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watershed 
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847
Why are ridges needed?
threshold
image
gradient magnitude
•Ridge markers define background region
•Without them, one object will spill over into background and disappear
markers
watershed 
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847
Another example
image |
markers |
gradient magnitude |
watershed |
S. Birchfield, Clemson Univ., ECE 847, http://www.ces.clemson.edu/~stb/ece847