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21/11/15 Duong Anh Duc - Digital Image Processing
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Digital Image Processing
Image Enhancement
Image Enhancement
Frequency domain methods
Frequency domain methods
21/11/15
21/11/15 Duong Anh Duc - Digital Image Processing
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Image Enhancement:
Image Enhancement:
Frequency domain methods
Frequency domain methods
The concept of filtering is easier to visualize in
The concept of filtering is easier to visualize in
the frequency domain. Therefore, enhancement
the frequency domain. Therefore, enhancement
of image
of image f(m,n)
f(m,n) can be done in the frequency
can be done in the frequency
domain, based on its DFT
domain, based on its DFT F(u,v)
F(u,v) .
.
This is particularly useful, if the spatial extent
This is particularly useful, if the spatial extent
of the
of the point-spread sequence
point-spread sequence
h(m,n)
h(m,n) is large.
is large.
In this case, the convolution
In this case, the convolution
g(m,n) = h(m,n)*f(m,n)
g(m,n) = h(m,n)*f(m,n)
may be computationally unattractive.
may be computationally unattractive.
Enhanced
Image
PSS
Given Image
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21/11/15 Duong Anh Duc - Digital Image Processing
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Frequency domain methods
Frequency domain methods
We can therefore directly design a transfer
We can therefore directly design a transfer
function
function H(u,v)
H(u,v) and implement the
and implement the
enhancement in the frequency domain
enhancement in the frequency domain
as follows:
as follows:
G(u,v) = H(u,v)*F(u,v)
G(u,v) = H(u,v)*F(u,v)
Enhanced
Image
Transfer Function
Given Image
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1-d Fourier transform of a sequence
Given a 1-d sequence s[k], k={…,-1,0,1,2,…,}
Fourier transform
Fourier transform is periodic with 2
Inverse Fourier transform
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1-d Fourier transform of a sequence
How is the Fourier transform of a sequence s[k]
related to the Fourier transform of the continuous
signal
Continuous-time Fourier transform