label two objects that share part of the same boundary separately

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!

Answer 1

[Steve Eddins]

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]

Thanks! That's pretty helpful!