Image Enhancement in the Spatial Domain

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Chapter 3

• Image Enhancement in the Spatial Domain

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Spatial Domain
???????
??????????????????????? pixel ?????????????????
image ?????????????? ?????????? pixel
???????????????????????
????????
?? spatial domain ???????????? image ????
f(x,y) ????? x ??? y ?????????????????????????????
??????????? Origin
??????????????????????????? Spatial Domain ???
Frequency Domain
?????????????????? Fourier Transform
??????????? ?????????????? ????????????? ?????????
????????????????? ???? ?????????????????
Frequency domain
???????? Spatial Domain ???????????????????????
xy ?????? ?????????????? ?? Domain
??? ??????????????????????????????
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Image Enhancement
Image Enhancement ????????????????????????????????
????????????? ????????? ?????????????????????????
(?????????????) ???????? ????????
??????????????????????????????????????????????????
?????????????????? ??????????????????????
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Image Enhancement in the Spatial Domain
??????????????????????????????????????????????
Spatial domain ?????? ?????????????? Spatial
domain ??????? ???????? ???????????????????????
????? f(x,y) ?????????????, g(x,y) ?????????????
??? T ??? Function ???????????????????????????
(x,y)
???????? T ???????? input ??????? pixel
?????????? (x,y) ?????????? ???? input ?????????
pixel ?? Neighbors ?????? (x,y)
???????????? ??????????????? Function ?????????
?????????????????????? ?? input
?????????? pixel (x,y) ??????????
?????????????????? smoothing filter ???????
input ??? pixel ????? pixel ??????? (x,y)
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Types of Image Enhancement in the Spatial Domain
- Single pixel methods - Gray level
transformations Example - Historgram
equalization - Contrast stretching -
Arithmetic/logic operations Examples -
Image subtraction - Image averaging - Multiple
pixel methods Examples Spatial filtering -
Smoothing filters - Sharpening filters
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Gray Level Transformation
?????? ??????????? intensity ???????????????????
intensity ????????????? ?????? function
??? r ??? input intensity ??? s ??? output
intensity
???????? Contrast enhancement
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Image Negative
???
Original digital mammogram
L-1
Output intensity
Negative digital mammogram
??
0
L-1
Input intensity
??
???
L ??????????????????
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Log Transformations
Application
Fourier spectrum
Log Tr. of Fourier spectrum
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Power-Law Transformations
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Power-Law Transformations Gamma Correction
Application
?????????? ???????
????????????? Monitor ??????
????????????? Monitor ???????
????????? Gamma correction
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Power-Law Transformations Gamma Correction
Application
??? MRI ??????? Gamma Correction ?????????
Gamma ????????
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Power-Law Transformations Gamma Correction
Application
?????????????????? ???? Gamma Correction ?????????
Gamma ????????
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Contrast Stretching
Before contrast enhancement
After
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Gray Level Slicing
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Bit-plane Slicing
Bit 7
Bit 6
Bit 5
Bit 3
Bit 2
Bit 1
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Histogram
Histogram ???????????????????????????????????
pixel ??? intensity ????????
??????
????????? ???? histogram ????????????????
????? pixel
??????????? ???? histogram ???????????????
????? pixel
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Histogram (cont.)
Contrast ?????????????????????????????????????????
???????????????????????????
?????? low contrast ???? histogram
??????????????? ????????
?????? high contrast ???? histogram
????????????? ????????????
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Histogram Processing
???????????????????????? intensity
???????????????????? histogram ??????????????????
???
- Histogram equalization
???????????? histogram ??????????????????????????
- Histogram matching
???????????? histogram ???????????????????????????
??
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Monotonically Increasing Function
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Histogram Equalization
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Histogram Equalization (cont.)
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Histogram Equalization (cont.)
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Histogram Equalization (cont)
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Histogram Equalization (cont.)
??????????
????????? Histogram Eq.
????????????? ???????????? Histogram
equalization ??????????? Low Contrast ??
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Histogram Matching
?????????????? Histogram ????????????? ????????
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Histogram Matching
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Local Enhancement
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Local Enhancement
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Local Enhancement
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Local Enhancement
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Logic Operations
AND
OR
Image mask (??????????????? Mask ?? filter)
Original image
?????????????? ROI Region of Interest
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Arithmetic Operation Subtraction
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Arithmetic Operation Subtraction (cont)
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Arithmetic Operation Image Averaging
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Arithmetic Operation Image Averaging (cont.)
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain
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Chapter 3 Image Enhancement in the Spatial Domain