Mean and Median Filters

1
Mean and Median Filters

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• ???????
• ??E9406011

2
Outline

• Introduction
• Mean Filter
• Median Filter
• Summary
• Demo

3
Introduction

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• ????????
• ???(frequency domain) ???????? ?? (????,
  ??)
• 
  ??????????
• ???(spatial domain) ??????? pixel value ???

?????????
g(x,y) T f(x,y) f(x,y) ?????? g(x,y)
???????? T -gt???????
4
Introduction

• ???????( ??? g(x,y) T f(x,y) )

Original
Original
y
y



(x,y)
(x,y)
Image f(x,y)
Image g(x,y)
x
x
g(x,y) T f(x,y) f(x,y) ?????? g(x,y)
???????? T -gt???????
5
Outline

• Introduction
• Mean Filter
• Median Filter
• Summary
• Demo

6
Mean Filter

• The Mean Filter is used to
• soften an image by averaging surrounding pixel
  values.

7
Mean Filter
Grayscale 3x3 pixel window
22 77 48
150 77 158
0 77 219
(x,y)
Center pixel ( 22 77 48 150 77 158
0 77 219 ) / 9 92
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Mean Filter
(a) ?????????? (b) ??????????? (c)
?????????? (d) ???????????
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Mean Filter

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int x , y int a(n-1)/2 int
color(i) , color(x,y) for(int kx-a kltxa
k) for(int my-a mltya
m) color(x,y)color(k,m) color(i)co
lor(x, y)/nn)
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Mean Filter

• ITK

Header file included include
itkMeanImageFilter.h Using Typedef
ItkMeanImageFilter lt
InputImageType, OutputImageType gt FilterType
FilterTypePointer filter
FilterTypeNew(() InputImageTypeSizeType
indexRadius indexRadius0 1 // radius
along x 1-gt 2D 2-gt 35 indexRadius1 1
// radius along y Rx 2 1 2 1
1 3 Rx ?? x ?????, 1 ????? Ry 2 1
2 1 1 3 Ry ?? y ?????, 1 ?????
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Mean Filter
Mean
Source
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Mean Filter
Source
Mean
13
Outline

• Introduction
• Mean Filter
• Median Filter
• Summary
• Demo

14
Median Filter

• The Median filter is used to
• remove noise from an image
• by replacing pixels with the middle pixel
  value selected from a certain window size.

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Median Filter
Grayscale 3x3 pixel window
22 77 48
150 77 158
0 77 219
(x,y)
0, 22, 48, 77, 77 , 77, 150, 158, 219
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Median Filter
(a) ?????????? (b) ??????????? (c)
?????????? (d) ???????????
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Median Filter

• ???

int x , y int z0 int a(n-1)/2 int color(i)
int array new int nxn-1 for(int kx-a
kltxa k) for(int my-a mltya
m) array zcolor(k,m) z sort(ar
ray) color(i)median(array )
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Median Filter

• ITK

Header file included include
itkMedianImageFilter.h Using Typedef
ItkMedianImageFilter lt
InputImageType, OutputImageType gt FilterType
FilterTypePointer filter
FilterTypeNew(() InputImageTypeSizeType
indexRadius indexRadius0 1 // radius
along x 1-gt 2D 2-gt 35 indexRadius1 1
// radius along y
19
Median Filter
33 median filtering
Source
20
Median Filter
Source
33 median filtering
99 median filtering
21
Outline

• Introduction
• Mean Filter
• Median Filter
• Summary
• Demo

22
Summary

• Mean filter and Median filter??? - 1

23
Summary

• Mean filter and Median filter??? - 2

Mean filter
Median filter
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Summary

• Mean filter and Median filter??? - 3

(c) ???????
25
Outline

• Introduction
• Mean Filter
• Median Filter
• Summary
• Demo

26
Demo
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Demo
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????

• ItkSoftwareGuide.pdf
• http//www.cee.hw.ac.uk/hipr/html/mean.html
• http//www.ntut.edu.tw/s9598008/homework1.htm
• http//www.cc.ntut.edu.tw/s8410010/hw1.htm
• ???,??????,??????(SIM 949)?
• http//140.128.102.71/ ?????????????

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