9 Image Processing I.pdf

7/29/2019 9 Image Processing I.pdf

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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


Gray scale perception is not linear

Contrast, length, orientation are notentirely linear


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Enhancing images Intensity transforms


Negative transformContrast StretchingLogarithm transform gamma factorThresholding(upper and lower)

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Enhancing images imadjust transform


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)


Image in

Imageout

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Image in

Imageout

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Image in

Imageo

ut

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Enhancing images gamma factor


Image in

Image in

Imageout

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gamma =1

Imageout

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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


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& resulting transform curves


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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global vs local processing


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Enhancing images Spatial Filtering &

Processing


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


Smoothing masks

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Spatial Smoothing Filter masks


Increasing mask size blurstheimage.


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Edge enhancement filter masks - Laplacian


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Edge enhancement filter masks other derivatives



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Image enhancement via multistage processing


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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

Documents

9 Image Processing I.pdf