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Image Thresholding

Image Thresholding. Thresholding is the simplest method of image segmentation. From a grayscale image, thresholding can be used to create binary images. Course Name: Digital Image Processing Level: UG. Authors Phani Swathi Chitta Mentor Prof. Saravanan Vijayakumaran.

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Image Thresholding

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  1. Image Thresholding Thresholding is the simplest method of image segmentation. From a grayscale image, thresholding can be used to create binary images Course Name: Digital Image Processing Level: UG Authors Phani Swathi Chitta Mentor Prof. Saravanan Vijayakumaran

  2. Learning Objectives After interacting with this Learning Object, the learner will be able to: • Understand how the thresholding of an image is done

  3. Definitions of the components/Keywords: 1 • During the thresholding process, individual pixels in an image are marked as “object” pixels if their value is greater than some threshold value (assuming an object to be brighter than the background) and as “background” pixels if their value is less than threshold value • Typically, an object pixel is given a value of “1” while a background pixel is given a value of “0” • The key parameter in the thresholding process is the choice of the threshold value 2 3 4 5

  4. Master Layout 1 Transformation graph Original Image 2 255 Output s 3 0 30 255 input r Graph for T=30 4 • Give a slider ranging from 0 to 255 so that user can select any one threshold value. • The graph should also vary along with the slider depending on threshold value. 5

  5. Threshold value 0 Step 1: 1 2 3 4 5

  6. Step 2: Threshold value 10 1 2 3 4 5

  7. Step 3: Threshold value 25 1 2 3 4 5

  8. Step 4: Threshold value 50 1 2 3 4 5

  9. Step 5: Threshold value 75 1 2 3 4 5

  10. Step 6: Threshold value 100 1 2 3 4 5

  11. Step 7: Threshold value 125 1 2 3 4 5

  12. Step 8: Threshold value 150 1 2 3 4 5

  13. Step 9: Threshold value 175 1 2 3 4 5

  14. Step 10: Threshold value 200 1 2 3 4 5

  15. Step 11: Threshold value 215 1 2 3 4 5

  16. Step 12: Threshold value 230 1 2 3 4 5

  17. Step 13: Threshold value 250 1 2 3 4 5

  18. Step 14: Threshold value 255 1 2 3 4 5

  19. Electrical Engineering Slide 1 Slide 3 Slide 20, 21 Slide 23 Slide 22 Introduction Definitions Analogy Test your understanding (questionnaire)‏ Lets Sum up (summary)‏ Want to know more… (Further Reading)‏ Interactivity: Try it yourself • Select any one of the figures • a b • c d • Select threshold value between 0 - 255 • Give a slider ranging from 0 to 255 so that user can select any one threshold value. 19 Credits

  20. Questionnaire 1 • Thresholding can be used to create binary images from Answers: a)colour image b) gray scale image c) Either a or b d)‏ Both a and b 2. If the threshold value is 200, what is the output of the given image Note: Gray colour value is 150 Answers: a) b) ‏ c) d) 2 3 4 5

  21. Questionnaire 1 3. If the threshold value is 125, what is the output of the given image Note: Gray colour value is 150 Answers: a)b)‏ c) d) 2 3 4 5

  22. Links for further reading Reference websites: http://en.wikipedia.org/wiki/Thresholding_%28image_processing%29 Books: Digital Image Processing- Rafael C. Gonzalez, Richard E. Woods, second edition, Pearson Education Research papers:

  23. Summary • Thresholding is the simplest method of image segmentation. From a grayscale image, thresholding can be used to create binary images • During the thresholding process, individual pixels in an image are marked as “object” pixels if their value is greater than some threshold value (assuming an object to be brighter than the background) and as “background” pixels if their value is less than threshold value • Typically, an object pixel is given a value of “1” while a background pixel is given a value of “0”

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