Image Processing Reference
In-Depth Information
Figure 8.5 Stack filter implementation. The output value at each stack level is a binary func-
tion of the thresholded inputs at the same level.
The stack filter may also be used to implement some rank-order and weighted-order
filters. In fact, the maximum operator is precisely the same as the erosion operator
described above. From the description of stacking in the previous chapter, the me-
dian filter may be implemented via a stack filter using the majority function. For
three inputs this may be written as
i
i
i
i
i
i
i
yxxxxxx
=⋅
+⋅
+⋅
0 .
(8.7)
01
1 2
This is shown in Fig. 8.7.
Stack filters consist of levels of independently computed values. This has the
advantage that each level may be implemented in parallel without reference to the
others. This means that what began as a gray level sorting operation, i.e.,
)
(
y
=
median
x
,
x
,
x
,
(8.8)
01 2
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