# label two objects that share part of the same boundary separately

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Joy on 3 Aug 2022
Commented: Joy on 3 Aug 2022
I have a matrix like this:
m = [0,1,1,1,0;1,0,0,0,1;0,1,1,1,0;0,1,0,1,0;0,0,1,0,0];
And I want to label the interior separately, which results in a matrix like this:
m1 = [0,1,1,1,0;1,2,2,2,1;0,1,1,1,0;0,1,3,1,0;0,0,1,0,0];
But I'm not sure how to do that. Any suggestion will be appreciated! Thank you!

Steve Eddins on 3 Aug 2022
m = [0,1,1,1,0;1,0,0,0,1;0,1,1,1,0;0,1,0,1,0;0,0,1,0,0]
m = 5×5
0 1 1 1 0 1 0 0 0 1 0 1 1 1 0 0 1 0 1 0 0 0 1 0 0
Fill the holes. From your example, it looks like the background connectivity should be 4.
filled_holes = imfill(m,4,'holes')
filled_holes = 5×5
0 1 1 1 0 1 1 1 1 1 0 1 1 1 0 0 1 1 1 0 0 0 1 0 0
The pixels that were added are the holes.
hole_pixels = filled_holes & ~m
hole_pixels = 5×5 logical array
0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0
Label the hole pixels.
L = bwlabel(hole_pixels,4)
L = 5×5
0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0
Add the labels (incremented by one) to the original matrix.
m_out = m;
m_out(hole_pixels) = L(hole_pixels) + 1
m_out = 5×5
0 1 1 1 0 1 2 2 2 1 0 1 1 1 0 0 1 3 1 0 0 0 1 0 0
Joy on 3 Aug 2022

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