image enhancement - southeast universitycse.seu.edu.cn/personalpage/bao.list/enhancement.pdf ·...
TRANSCRIPT
![Page 1: Image Enhancement - Southeast Universitycse.seu.edu.cn/PersonalPage/bao.list/Enhancement.pdf · 2011-fall LIST 20 1. Z Chen, R R Abidi, D L Page, and M A Abidi, 'Gray-level grouping](https://reader031.vdocuments.net/reader031/viewer/2022020215/5b6965ac7f8b9af77c8df1c1/html5/thumbnails/1.jpg)
Image Enhancement
![Page 2: Image Enhancement - Southeast Universitycse.seu.edu.cn/PersonalPage/bao.list/Enhancement.pdf · 2011-fall LIST 20 1. Z Chen, R R Abidi, D L Page, and M A Abidi, 'Gray-level grouping](https://reader031.vdocuments.net/reader031/viewer/2022020215/5b6965ac7f8b9af77c8df1c1/html5/thumbnails/2.jpg)
Image Qualities
• Gray distribution
– Gray level mapping
• Noise level
– Image smoothing
• Contour sharpness
– Image sharpening
2011-fall LIST 2
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Gray Histogram
2011-fall LIST 3
Histogram h(rk) = nk rk=[0, L-1]
kyx
k ryxfcountn ),(),(
nnrhk
k
k
k )(
normalized histogram :
n
n
n
rhrp kkk
)()(
1)(0 krp
1)( k
krpprobability density
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Gray Histogram
2011-fall LIST 4
0
200
400
600
800
1000
0 50 100 150 200 250
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Gray Histogram
2011-fall LIST 5
0
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6000
0 50 100 150 200 250
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Gray Histogram
2011-fall LIST 6
0
0.5
1
1.5
2
2.5
x 104
0 50 100 150 200 250
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Gray Histogram
2011-fall LIST 7
0
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5000
0 50 100 150 200 250
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Gray Histogram
2011-fall LIST 8
0
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6000
0 50 100 150 200 250
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Gamma Correction
2011-fall LIST 9
inout II
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Gamma Correction
2011-fall LIST 10
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Gray Mapping
2011-fall LIST 11
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2011-fall LIST 12
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2011-fall LIST 13
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Histogram Equalization
2011-fall LIST 14
PDF:
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Histogram Equalization
2011-fall LIST 15
0
500
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3000
3500
4000
4500
5000
0 50 100 150 200 250
0
500
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1500
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2500
3000
3500
4000
4500
5000
0 50 100 150 200 250
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2011-fall LIST 16
R
B
G (0,0,0)
(1,0,0)
(0,1,0)
(0,0,1)
Red
Blue
Green
Yello
Black
White
Cyan
Magenta
红 黄
绿
青
品红
蓝
RGB
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2011-fall LIST 17
Additive System Subtractive System
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2011-fall LIST 18
HSI
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Color Image Histogram Equalization
2011-fall LIST 19
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2011-fall LIST 20
1. Z Chen, R R Abidi, D L Page, and M A Abidi, 'Gray-level grouping (GLG) : an automatic method for optimized image contrast enhancement – part I : the basic method', IEEE Trans Image Proc, 15(8), 2006 : 2290-2302
2. N Bassiou, C Kotropoulos, ‘Color image histogram equalization by absolute discounting back-off’, Computer Vision and Image Understanding, Vol 107, 2006: 108-122
Assignment
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Image Smoothing
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Spectrum Properties
2011-fall LIST 22
0 50 100 150 200 250 30050
100
150
200
250
300
gray levels on line 256
0 50 100 150 200 250 3000
500
1000
1500
2000
2500
3000
spectrum on line 256
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Spectrum Properties
2011-fall LIST 23
0 50 100 150 200 250 30050
100
150
200
250
300
0 50 100 150 200 250 3000
500
1000
1500
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2500
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Gaussian noise
μ = 0 σ=0.01
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2011-fall LIST 24
0 50 100 150 200 250 30050
100
150
200
250
300
0 50 100 150 200 250 30050
100
150
200
250
300
0 50 100 150 200 250 3000
500
1000
1500
2000
2500
3000
gray levels spectrum
original signal
with noise
0 50 100 150 200 250 3000
500
1000
1500
2000
2500
3000
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Image Averaging
2011-fall LIST 25
tt
tnN
ItIN
I )(1
)(1
Original Image without noise: I
Samples of original image with noise : I(t), (t=0,1,...,N-1)
)()( tnItI n(t) → Gaussian distribution
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sample 8 frames averaging 16 frames averaging
64frames averaging 128frames averaging
2011-fall 26 LIST
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2011-fall 27 LIST
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Lowpass Filter
2011-fall LIST 28
G(u,v) = H(u,v) F(u,v)
H(u,v) : filter transfer function
F(u,v) : image in frequency domain
G(u,v) : output in frequency domain
g(x,y) = h(x,y) f(x,y)
h(x,y) : point spread function
Linear Filter H(·)
F(u,v) G(u,v)
u
|F(u)|
u0 0
0
1)u(H
(|u|≤u0)
otherwise
Understanding of Lowpass Filter H(u)
Noise ↔ Edge
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Lowpass Filter
2011-fall LIST 29
Ideal lowpass filter
point spread function
0 20 40 60 80 100 120 140-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
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Lowpass Filter
2011-fall LIST 30
Gaussian filter
22 2/)( uAeuH 22222)( xAexh
0 20 40 60 80 100 120 1400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 1400.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
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Lowpass filter
2011-fall LIST 31
Average filter
0 20 40 60 80 100 120 140-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
transfer function
0 20 40 60 80 100 120 1400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
point spread function
otherwise
axaxh
0
)2/2/(1)(
2/
2/
2)(a
a
uxj dxeuH
uj
ee aujauj
2
u
au
)sin(
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2011-fall LIST 32
0 50 100 150 200 250 3000
50
100
150
200
250
300
0 50 100 150 200 250 30020
40
60
80
100
120
140
160
0 50 100 150 200 250 30040
60
80
100
120
140
160
180
average filter
original image 3x3 5x5
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2011-fall LIST 33
0 50 100 150 200 250 3000
50
100
150
200
250
300
Gaussian filter
original image σ=0.5
0 50 100 150 200 250 30040
60
80
100
120
140
160
180
200
220
240
0 50 100 150 200 250 30020
40
60
80
100
120
140
160
180
σ=1.0
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Median Filter
2011-fall LIST 34
nonlinear filter
median value
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2011-fall LIST 35
0 50 100 150 200 250 3000
50
100
150
200
250
300
0 50 100 150 200 250 3000
50
100
150
200
250
3x3 median filter original image
0 50 100 150 200 250 3000
50
100
150
200
250
5x5 median filter
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Image Sharpening
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Edges
2011-fall LIST 37
x
G(x)
x
G(x)
x
G(x)
Ideal Edge
Sharp Edge
Blurred Edge
Edge ↔ Noise
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2011-fall LIST 38
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2011-fall LIST 39
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2011-fall LIST 40
Median Filter Gaussian Filter Average Filter
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2011-fall LIST 41
Median Filter Gaussian Filter
Average Filter
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2011-fall LIST 42
Gaussian Filter
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2011-fall LIST 43
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2011-fall LIST 44
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Unsharp Masking
2011-fall LIST 45
Low Pass
High Pass
+
×
Input f(x,y) Output g(x,y)
α
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2011-fall LIST 46
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2011-fall LIST 47
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2011-fall LIST 48
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2011-fall LIST 49
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Contrast Enhancement
2011-fall LIST 50
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2011-fall LIST 51
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2011-fall LIST 52
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2011-fall LIST 53
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2011-fall LIST 54