Issues with imfill() function

I am trying to fill in objects like the above. I think that the function 'imfill()' is not working because the hole is technically open - the boundary of the object does not completely surround the "hole" inside. My goal is to completely fill in the holes (so that I can later automatically segment them). Any recommendations are appreciated!

Answer 1

[Tomás Franco]

Have you considered performing morphological operations such as closing, to close that gap?