
Formally, the dilation can be defined by
A
!
B ¼
[
a2A
B
a
(8:3)
Dilation has the effect of expanding the object, filling small holes in and
intrusions into the object (Fig. 8.2b), while erosion has a shrinking effect,
enlarging holes and eliminating small extrusions (Fig. 8.2a).
Since dilation by a disk expands an object and erosion by a disk shrinks
an object, they can be combined to find object boundaries in binary images.
The three possibilities are: (1) the external boundary (dilation minus the image), (2)
the internal boundary (the image minus the erosion), and (3) the morphological
gradient (dilation minus erosion), which is the boundary that straddles ...