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ENGG 167
MEDICAL IMAGING
Lecture9: Thursday Oct. 12
Image Processing IImage Types & Linear Transforms
Reference: Gonzalez, Woods, EddinsDigital Image Processing using MATLAB, Prentice Hall, (2004)
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Preparation -
Review Imaging Processing Toolbox Help Manual(on your computer)
Download NIHImage(Mac) / ImageJ (Windows)(from the web just do a Google search)
Most of the next two lectures are adapted fromTextbook by Gonzalez, Woods, EddinsDigital Image Processing using MATLAB, Prentice Hall, (2004)
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Human light perception is sensitive but not linear
Ref: Gonzalez et al, Text
Gray scale perception is not linear
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This leads to optical illusion in certain cases
Ref: Gonzalez et al, Text
Gray scale perception is not linear
Contrast, length, orientation are notentirely linear
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Enhancing images Intensity transforms
Ref: Gonzalez et al, Text
Negative transformContrast StretchingLogarithm transform gamma factorThresholding(upper and lower)
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Enhancing images imadjust transform
Ref: Gonzalez et al, Text
Negative transform of image fg = imadjust(f, [low_inhigh_in], [low_outhigh_out], gamma);
g =imadjust(f, [0 1], [1 0]); or g =imcomplement(f);
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Enhancing images contrast stretching
(Radiology: windowing)
Ref: Gonzalez et al, Text
Image in
Imageout
Low I high I
LowI
highI
Image in
Imageout
Low I high I
LowI
highI
Image in
Imageo
ut
Low I high I
LowI
highI
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Enhancing images gamma factor
Ref: Gonzalez et al, Text
Image in
Image in
Imageout
Low I high I
LowI
highI
gamma =1
Imageout
Low I high I
LowI
highI
gamma 1
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Enhancing images Histogram transforms in
paint shop pro
Ref: visible human project
midtonecompression
midtoneexpansion
Histogram stretch
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Enhancing images Histogram transform
(histogram equalization, stretching)h(rk) =nk the histogram, h, is the number of pixels, n, at each k intensitylevel, with r being the new scale level ordinate
Grey scale values0 255
#ofpixels
Grey scale values 2550
#ofpixels
Ref: visible human project
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Enhancing images Histogram processing
& resulting transform curves
Ref: Gonzalez et al, Text
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Enhancing images Histogram processing
& resulting transform curves
Ref: Gonzalez et al, Text
Scanned image (text on either side ofpage is showingthrough!) Removing this
large peak at thetop of the intensity
range eliminates allthis crosstalk
Repeating again onthis edge correctsthis locally
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Enhancing images Histogram processing
global vs local processing
Ref: Gonzalez et al, Text
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Enhancing images Spatial Filtering &
Processing
Ref: Gonzalez et al, Text
1) Linear spatial filtering
2) Nonlinear spatial filtering
3) Geometric transformations
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Spatial Filtering with a filter mask to map the
initial image onto a new calculated image
Ref: Gonzalez et al, Text
Smoothing masks
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Spatial Smoothing Filter masks
Ref: Gonzalez et al, Text
Increasing mask size blurstheimage.
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Edge enhancement filter masks - Laplacian
Ref: Gonzalez et al, Text
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Edge enhancement filter masks other derivatives
Ref: Gonzalez et al, Text
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Image enhancement via multistage processing
Ref: Gonzalez et al, Text
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Assignments this week
Image Processing with MATLAB: Due Wed. Oct. 18.Download assignement.Choose one Function in MATLAB Image processing toolbox and describe anddemonstrate the function, with an example.
Options :Dilation and ErosionImage DeblurringColor space transformLinear Filter design
Radon TransformSegmentationSomething else?
1) Use an image and show the effect that can be achieved with the MATLAB function.2) Show when the effect is dominant and when it is not dominant (what are the main
control parameters).3) Include all MATLAB programs in your handed in work, as well as all images
J ournal Club Presentations: Monday, Oct. 16.Image processing paper