If you use a integer or double class, it's
1 1 1
1 1 1
1 1 1
which is the same as
se = ones(3); % <= double, or:
se = ones(3, 'uint8'); % <= uint8
or for a logical / boolean class:
true true true
true true true
true true true
which is the same as
se = true(3);
You can also use the strel function
se = strel('disk', 5);
where se is a special class of type 'strel'.
I usually use the logical form when I make up a structuring element manually.
