Watershed algorithm: why is my 4-connected watershed 8-connected?
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Jennika Hammar
on 3 Feb 2020
Answered: Image Analyst
on 3 Feb 2020
Hello,
I did watershed segmentation of my image using the distance transform. I wonder why I get a 8-connected watershed when specifying a 4-connectivty and vice versa?
i_ws4 = watershed(im, 4);
imshow(i_ws4)
![b4.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/269714/b4.png)
i_ws8 = watershed(im);
imshow(i_ws8)
![b8.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/269715/b8.png)
Thanks
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Accepted Answer
Image Analyst
on 3 Feb 2020
With your top image, the four white blobs are separated according to 4-connectivity. That is, they touch at the pixel corners but that is not considered to be a connection like they're the same blob.
However with 8 connectivity they WOULD be connected, so it had to make the black lines larger so that the four white blobs don't touch each other, even at the pixel corners.
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