Presentation is loading. Please wait.

Presentation is loading. Please wait.

Medical Image Analysis Dr. Mohammad Dawood Department of Computer Science University of Münster Germany.

Similar presentations


Presentation on theme: "Medical Image Analysis Dr. Mohammad Dawood Department of Computer Science University of Münster Germany."— Presentation transcript:

1 Medical Image Analysis Dr. Mohammad Dawood Department of Computer Science University of Münster Germany

2 2 Medical Imaging, SS-2014 Dr. Mohammad Dawood Recap

3 3 Medical Imaging, SS-2014 Dr. Mohammad Dawood Grayscale transformations 1.Linear 2.Logarithmic 3.Power law Point operations Local operators 1.Histogram Equalization 2.Adpative/Local Hist Eq 3.Color space 4.Fourier transform 5.Spatial filtering

4 4 Medical Imaging, SS-2014 Dr. Mohammad Dawood Edge detection

5 5 Medical Imaging, SS-2014 Dr. Mohammad Dawood What is an “edge”? Discontinuity in Image brightness

6 6 Medical Imaging, SS-2014 Dr. Mohammad Dawood *=*= Recognizing the edge

7 7 Medical Imaging, SS-2014 Dr. Mohammad Dawood *=*= Increasing edge thickness - easier to detect and better connected edges

8 8 Medical Imaging, SS-2014 Dr. Mohammad Dawood *=*= Strengthening the edges

9 9 Medical Imaging, SS-2014 Dr. Mohammad Dawood Edge detection with spatial operators Prewitt operators

10 10 Medical Imaging, SS-2014 Dr. Mohammad Dawood Adding operators =+=

11 11 Medical Imaging, SS-2014 Dr. Mohammad Dawood Derivatives of an image Magnitude of gradient: Angle:

12 12 Medical Imaging, SS-2014 Dr. Mohammad Dawood 1 First derivative Forward difference Backward difference Central difference MRI Spinefw bw cdbw_i bw+bw_i

13 13 Medical Imaging, SS-2014 Dr. Mohammad Dawood Laplace operator H+V Laplace

14 14 Medical Imaging, SS-2014 Dr. Mohammad Dawood Cardiac PET

15 15 Medical Imaging, SS-2014 Dr. Mohammad Dawood Gaussian+Gradient *=*=

16 16 Medical Imaging, SS-2014 Dr. Mohammad Dawood Sobel operators Edge detection with spatial operators

17 17 Medical Imaging, SS-2014 Dr. Mohammad Dawood =+=

18 18 Medical Imaging, SS-2014 Dr. Mohammad Dawood Scharr operators Edge detection with spatial operators

19 19 Medical Imaging, SS-2014 Dr. Mohammad Dawood Roberts operators Edge detection with spatial operators +

20 20 Medical Imaging, SS-2014 Dr. Mohammad Dawood Canny operator 1.Gaussian for noise reduction 2.Calculation of edges (sobel operator) 3.Non-maximum suppression, no neighbor should have a higher gradient except in the same direction 0 : if intensity > the intensities in the N and S directions 45 : if intensity > the intensities in the NW and SE directions 90 : if intensity > the intensities in the W and E directions 135 : if intensity > the intensities in the NE and SW directions 4.Hysteresis delete edges below threshold 1 keep edges above threshold 2 keep edges between thresholds, if one neighbor is above threshold 2

21 21 Medical Imaging, SS-2014 Dr. Mohammad Dawood Canny operatorth=0.5 th=0.1

22 22 Medical Imaging, SS-2014 Dr. Mohammad Dawood Marr-Hildreth operator Laplacian of the Gaussian (LoG)

23 23 Medical Imaging, SS-2014 Dr. Mohammad Dawood Marr Hildreth operator sigma=1 sigma=2

24 24 Medical Imaging, SS-2014 Dr. Mohammad Dawood Hough Transform

25 25 Medical Imaging, SS-2014 Dr. Mohammad Dawood 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

26 26 Medical Imaging, SS-2014 Dr. Mohammad Dawood Hough transform for detecting lines Alternative definition of lines

27 27 Medical Imaging, SS-2014 Dr. Mohammad Dawood Hough transform Similar transforms can be defined for circles, ellipses or other parametric curves

28 28 Medical Imaging, SS-2014 Dr. Mohammad Dawood Morphological operations

29 29 Medical Imaging, SS-2014 Dr. Mohammad Dawood 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

30 30 Medical Imaging, SS-2014 Dr. Mohammad Dawood Erosion If A is an image and B is a structure element then X

31 31 Medical Imaging, SS-2014 Dr. Mohammad Dawood Dilation X

32 32 Medical Imaging, SS-2014 Dr. Mohammad Dawood Closing Dilation + Erosion

33 33 Medical Imaging, SS-2014 Dr. Mohammad Dawood Opening Erosion + Dilation


Download ppt "Medical Image Analysis Dr. Mohammad Dawood Department of Computer Science University of Münster Germany."

Similar presentations


Ads by Google