Image Processing and Computer Vision

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Image Processing and Computer Vision

• Edge Detection
• Generalized Hough Transform

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Edge Detection
Contour edge

• Edge ?? 2 ????
• Contour edge
• Texture edge

Texture edge
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Edge Detection

• ???????? Edge ????????????? pixel ?????????????
  ?????????????????????? intensity ??? ? ???? ???
  0-255 ??????? 255-0

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Edge Filter (Robert Operator)
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Example (Robert operator)
Gx
Gray scale Image
Gy
G
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Edge Filter (Prewitt Operator)
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Edge Filter (Sobel Operator)
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Edge Filter (Canny Operator)

• d. Canny operator
• Ii,j image
• Convolution image by Gaussian Filter we will
  get
• Si,j Gi,j ? Ii,j
• ? spread of gaussian (??????????????? gaussian
  filter)
• ?????????? filter ???????
• Pi,j (Si,j1 Si,j Si1,j1
  Si1,j) / 2
• Qi,j (Si,j Si1,j Si,j1
  Si1,j1) /2

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Edge Filter (Canny Operator)

• -Edge pixel
• Mi,j ? Pi,j2 Qi,j2
• - Each ? in edge pixel
• ?i,j arctan(Qi,j, Pi,j)

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Sample Image
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Generalized Hough Transform

• ?????????????????? ? ?? ???????????????? (Target
  Image)
• ?????????????? 2 ???????? ? ???
• ??????????????????????? ? ??? Template
  shape???????
• ????????????????? (shape) ????????????????(Target
  image)

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Learn Shape

• ?????????? Shape ?????????? Template ??????????

• ?????????????????????????????????
• ?????? pixel ??????? edge ??????
• ???????????????????????? ????????????
• ??????? ? ??????
• ? ????????????????? X
• ? ??? gradient ??????????????
• edge detector
• r ????????????????????????????
• ???????????

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GHT R-Table
????? R-Table ?????? ??????????????????? ?
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Search for Shapes
Target Image
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Search for Shape

• Algorithm ?????? search ?????????????(Target)
• 1. ?????????? ?????????????????
  ??????????????? ? (gradient direction)
• ???
• 2. ????????? ? edge pixel ?????? ? ???????????? 1
  ??????????????????
• ? ??? r ?????????????? R-Table
• 3. ???????????? ? ??? r ???????????????????
  R-Table ??? ? ???? ????????
• ????????? ? ??? r ??????
• xc x rcos(?)
• yc y rsin(?)
• 4. ????? Vote xc ??? yc ????????????????????
  Maximum vote
• ??? xc ??? yc ????????????????????????????????
  ????????????? template
• ????????? target

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Search for Shapes
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Case when Image Scale or Rotate
Scale factor S Rotation factor ? ??????????
Array ???? 4 ???? ???????????????? Vote ??????
Arrayxc, yc, S, ? ??????? S
???????????????? 0.1, 0.2, 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3,
1.4, 1.5 ??????? R ??????????????? 0-359
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Case when Image Scale or Rotate

• ????????????????? Scale ??? Rotation
  ??????????????????????????????????????????????????
  ???????? ??????

xc x rcos(?) yc y rsin(?)
xc x r S cos(? ?) yc y r S
sin(? ?)
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Case when Image Scale or Rotate

• Algorithm
• 1. For each (?, r) from R-Table
• For each S 0.3 to 1.5
• For each ? 0 to 359 find
• Arrayxc, yc, S, ?
• Look for Maximum vote in 4-D Array

xc x r S cos(? ?) yc y r S
sin(? ?)
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Example
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Example
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Example
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Example