Determination of the apparent boundary of an object

The notions of the apparent boundary and the strict apparent boundary of an object, which provide an automatic approach of boundary detection, are presented. It is shown that the apparent boundary and the strict apparent boundary have the same diameter and the same convex hull as the original object. It is also shown that the strict apparent boundary is weakly externally visible, and is a fixpoint of the two operators that find the apparent boundary and the strict apparent boundary.< >