Transcript Folie 1 - uni

Medical Imaging
Mohammad Dawood
Department of Computer Science
University of Münster
Germany
Medical Imaging, SS-2011
Recap
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Grayscale transformations
1. Linear
2. Logarithmic
3. Power law
Point operations
Local operators
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Histogram Equalization
Adpative/Local Hist Eq
Color space
Fourier transform
Spatial filtering
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Edge detection
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Recognizing the edge
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Increasing edge thickness
- easier to detect and better connected edges
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Strengthening the edges
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Edge detection with spatial operators
Prewitt operators
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Adding operators
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Derivatives of an image
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Magnitude of gradient:
Angle:
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First derivative
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Forward difference
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Backward difference
Central difference
MRI Spine
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cd
bw_i
bw+bw_i
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Laplace operator
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H+V
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Laplace
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Cardiac PET
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Gaussian+Gradient
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Edge detection with spatial operators
Sobel operators
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Edge detection with spatial operators
Scharr operators
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Edge detection with spatial operators
Roberts operators
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Canny operator
Gaussian for noise reduction
Calculation of edges in four directions (sobel operator)
non-maximum suppression
angle zero: if intensity >the intensities in the N and S directions
angle is 90: if intensity >the intensities in the W and E directions
angle is 135: if intensity >the intensities in the NE and SW directions
angle is 45 degrees: if intensity >the intensities in the NW and SE directions
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Canny operator
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th=0.1
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Marr-Hildreth operator
Laplace of the Gaussian (LoG)
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Marr Hildreth operator
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sigma=1
sigma=2
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Marr Hildreth operator
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Hough Transform
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Hough transform for detecting lines
A line can be defined as:
Take the edge map of the image I
Look for the neighbors of a pixel and
determine m and b
Accumulate the m and b in an accumulator
array
Find the maxima of the accumulator array
Transform them back to image space
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Hough transform for detecting lines
Alternative definition of lines
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Hough transform
Similar transforms can be defined for circles,
ellipses or other parametric curves
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Morphological operations
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Morphological operators
Operations are based on Set Theory and require a structure element
Basic morphological operations are:
1. Erosion
2. Dilation
3. Opening
4. Closing
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Erosion
If A is an image and B is a structure element then
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Dilation
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Closing
Dilation + Erosion
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Opening
Erosion + Dilation
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