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### 1

1. 1. Image Processing
2. 2. Image Processing <ul><li>We will find out: </li></ul><ul><li>How images are processed to eliminate noise </li></ul><ul><li>How to calculate the mean and medium values of pixels </li></ul>
3. 3. Smoothing… <ul><li>Images are smoothed by replacing each pixel with the mean value of it and its neighbours. </li></ul><ul><li>This smoothes any edges that are present </li></ul><ul><li>This pixel’s value is replaced by the average of its value and its 8 neighbours </li></ul>200 100 100 200 100 100 200 100 100
4. 4. Smoothing… <ul><li>Smoothing reduces the appearance of edges </li></ul><ul><li>Edges are smoothed out… </li></ul>166 133 100 166 133 100 166 133 100
5. 5. Removing Noise <ul><li>Noise is removed by replacing pixel with median value of its value and its neighbours </li></ul><ul><li>Before processing, this pixel contains noise.. </li></ul>100 100 100 100 255 100 100 100 100
6. 6. Removing Noise <ul><li>Noise is removed by replacing pixel with median value of its value and its neighbours </li></ul><ul><li>This pixel’s value is replaced by the median of its own value and its 8 neighbours </li></ul>100 100 100 100 100 100 100 100 100
7. 7. Finding Edges <ul><li>Subtract the N, S, E and W neighbours from 4 times the pixels value… </li></ul><ul><li>Subtract 200+200+200+200 from 4 x 200 = 0 </li></ul>This creates a distinct edge if there are variations across an image If there is no edge the image stays ‘smooth’ 200 200 200 200 200
8. 8. Finding Edges <ul><li>Subtract the N, S, E and W neighbours from 4 times the pixels value… </li></ul><ul><li>This pixel’s value is replaced by the median of its 8 neighbours </li></ul>200 200 200 200 200
9. 11. Edge enhancement in the retina Compare these grey squares. Do they look the same, or different
10. 12. Edge enhancement in the retina Now compare them. What do you notice? A B
11. 13. Edge enhancement in the retina What about this way? What do you notice? A B
12. 14. Edge enhancement in the retina Now move them closer . . . What happens? Which is darker? A B
13. 15. Edge enhancement in the retina Now swap them What happens? Which is darker? A B