Fill 4-connected cells exclusively

Dear all,

yesterday a asked a question about how to fill 4-connected cells. Several comments about the use of 'imfill' were given to me. I thank the contributors for them but the option chosen does not give exactly what I need. The example matrix that I gave was probably not a good one.

I show another example. If:

BW1 = logical([1 0 0 0 0 0 0 0
1 1 1 1 1 0 0 0
1 0 0 0 1 0 1 0
1 0 0 0 1 1 1 0
1 1 1 1 0 1 1 1
1 0 0 1 1 0 1 0
1 0 0 0 1 0 1 0
1 0 0 0 1 1 1 0]);

with the command:

    BW2 = imfill(BW1,4,'holes');

you get:

BW2 =

1 0 0 0 0 0 0 0
1 1 1 1 1 0 0 0
1 1 1 1 1 0 1 0
1 1 1 1 1 1 1 0
1 1 1 1 1 1 1 1
1 0 0 1 1 1 1 0
1 0 0 0 1 1 1 0
1 0 0 0 1 1 1 0

but I would like to fill only the cells with 0 which are 4-connected with 1s, that is, I would like to get the following matrix instead:

BW3 =

1 0 0 0 0 0 0 0
1 1 1 1 1 0 0 0
1 0 0 0 1 0 1 0
1 0 0 0 1 1 1 0
1 1 1 1 1 1 1 1
1 0 0 1 1 0 1 0
1 0 0 0 1 0 1 0
1 0 0 0 1 1 1 0

Do you know if there is an easy way to get this?

Again, thank you in advance.

Answer 1

[Steve Eddins]

I assume you meant your sample matrices to be 8-by-8 instead of 1-by-64? If that's true, then it looks like you want to change a pixel from a 0 to a 1 only if all of its 4-connected neighbors are 1. The following code uses bwhitmiss to identify such pixels:

se1 = [0 1 0; 1 0 1; 0 1 0];
se2 = [0 0 0; 0 1 0; 0 0 0];
pixels_to_change = bwhitmiss(BW1, se1, se2);

Now just elementwise-or with the original matrix:

BW3 = BW1 | pixels_to_change