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21/11/15 Duong Anh Duc - Digital Image Processing
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Digital Image Processing
Image Enhancement
Image Enhancement
Spatial Filtering
Spatial Filtering
21/11/15
21/11/15 Duong Anh Duc - Digital Image Processing
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Image Enhancement:
Image Enhancement:
Spatial Filtering
Spatial Filtering
Image enhancement in the spatial domain
Image enhancement in the spatial domain
can be represented as:
can be represented as:
g(m,n) = T(f)(m,n)
g(m,n) = T(f)(m,n)
The transformation
The transformation T
T maybe linear or
maybe linear or
nonlinear. We will mainly study linear
nonlinear. We will mainly study linear
operators
operators T
T but will see one important
but will see one important
nonlinear operation.
nonlinear operation.
Enhanced
Image
Transformation
Given Image
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21/11/15 Duong Anh Duc - Digital Image Processing
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How to specify
How to specify T
T
If the operator
If the operator T
T is linear and shift
is linear and shift
invariant (LSI), characterized by the point-
invariant (LSI), characterized by the point-
spread sequence (PSS)
spread sequence (PSS) h(m,n)
h(m,n) , then
, then
(recall convolution)
(recall convolution)
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21/11/15 Duong Anh Duc - Digital Image Processing
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How to specify
How to specify T
T
In practice, to reduce computations,
In practice, to reduce computations, h(m,n)
h(m,n) is
is
of “finite extent:
of “finite extent:
h
h(
(k,l
k,l)
) = 0
= 0 for
for
(
(k,l
k,l)
)
where
where is a small set (called neighborhood).
is a small set (called neighborhood). is
is
also called as the support of
also called as the support of h
h.
.
In the frequency domain, this can be represented
In the frequency domain, this can be represented
as:
as:
G
G(
(u,v
u,v) =
) = H
He
e(
(u,v
u,v)
) F
Fe
e(
(u,v
u,v)
)
where
where H
He
e(
(u,v
u,v) and
) and F
Fe
e(
(u,v
u,v) are obtained after
) are obtained after
appropriate zeropadding.
appropriate zeropadding.
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21/11/15 Duong Anh Duc - Digital Image Processing
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How to specify
How to specify T
T
Many LSI operations can be interpreted
Many LSI operations can be interpreted
in the frequency domain as a “filtering
in the frequency domain as a “filtering
operation.” It has the effect of filtering
operation.” It has the effect of filtering
frequency components (passing certain
frequency components (passing certain
frequency components and stopping
frequency components and stopping
others).
others).
The term
The term filtering
filtering is generally
is generally
associated with such operations.
associated with such operations.