
nor does it hold for grayscale morphological reconstruction. As mentioned
earlier, only symmetrical structuring elements are discussed in this chapter.
8.3.2 Erosion and Dilation
Grayscale erosion (dilation) of an image, f, by a flat structuring element D is
equivalent to a moving-minimum (moving-maximum) filter over the window
defined by the structuring element. Thus, erosion f
@
D and dilation f
!
D in this
case are simply special cases of order-statistic filters:
( f
@
D)(x) ¼ min f (z ) : z 2 D
x
fg
( f
!
D)(x) ¼ max f (z) : z 2 D
x
fg
(8:20)
An example of erosion by a disk on a grayscale image is shown in Fig. 8.11. The
two images on the left, input and eroded,