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Histogram Equalization of Grey Scale Images

Histogram Equalization of Grey Scale Images. Histogram equalization is a technique for adjusting image intensities to enhance contrast. Course Name: Digital Image Processing Level: UG. Authors Phani Swathi Chitta Mentor Prof. Saravanan Vijayakumaran.

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Histogram Equalization of Grey Scale Images

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  1. Histogram Equalization of Grey Scale Images Histogram equalization is a technique for adjusting image intensities to enhance contrast. Course Name: Digital Image Processing Level: UG Authors Phani Swathi Chitta Mentor Prof. Saravanan Vijayakumaran *The contents in this ppt are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 2.5 India license

  2. Learning Objectives After interacting with this Learning Object, the learner will be able to: • Explain how the grey scale image is enhanced using histogram equalization

  3. Definitions of the components/Keywords: 1 • Histogram equalization is a method in image processing of contrast adjustment using the image's histogram. • Histogram equalization can be used to improve the visual appearance of an image. • Calculate the Cumulative Distribution Function (CDF) of the image using formula: • where CDF[k] is the CDF value of pixel with value k in input image, • is the number of pixels with value j and N is the total number of • pixels. • Re-label all input pixels with corresponding values CDF[k]. 2 3 4 5

  4. Master Layout 1 The Low contrast Image Image after equalization 2 3 4 • Show two graphs: • 1. Histogram of low contrast image • 2. Histogram of equalized image 5

  5. Step 1: 1 2 3 4 5

  6. Step 1Contd... Histogram of low contrast image Histogram of equalized image

  7. Electrical Engineering Slide 1 Slide 3 Slide 10, 11,12 Slide 13 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 the filter size 7 Credits

  8. Questionnaire 1 1. What is the histogram for the image shown? Answers: a) b) 2 3 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 No. of pixels No. of pixels 4 5 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Gray level intensity Gray level intensity

  9. Questionnaire 1 1. Question 1 cont’d... What is the histogram for the image shown? Answers: c)d) 2 3 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 No. of pixels No. of pixels 4 5 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Gray level intensity Gray level intensity

  10. Questionnaire 1 2. What is the CDF for the image shown? Answers: a)b) 2 3 4 5

  11. Questionnaire 1 2. Question 2 cont’d... What is the CDF for the image shown? Answers: c) d) 2 3 4 5

  12. Questionnaire 1 3. What is the equalized histogram for the image shown? Answers: a) 2 3 8 7 6 5 4 3 2 1 No. of pixels 4 5 0 63.75 127.5 191.25 255 Gray level intensity

  13. Questionnaire 1 3. Question 3 cont’d... What is the equalized histogram for the image shown? Answers: b) 2 3 8 7 6 5 4 3 2 1 No. of pixels 4 5 0 63.75 127.5 191.25 255 Gray level intensity

  14. Questionnaire 1 3. Question 3 cont’d... What is the equalized histogram for the image shown? Answers: c) 2 3 8 7 6 5 4 3 2 1 No. of pixels 4 5 0 63.75 127.5 191.25 255 Gray level intensity

  15. Questionnaire 1 3. Question 3 cont’d... What is the equalized histogram for the image shown? Answers: d) 2 3 8 7 6 5 4 3 2 1 No. of pixels 4 5 0 63.75 127.5 191.25 255 Gray level intensity

  16. Links for further reading Reference websites: http://en.wikipedia.org/wiki/Histogram_equalization http://math.uci.edu/icamp/courses/math77c/demos/hist_eq.pdf http://nature.berkeley.edu/~bingxu/UU/spatial/Week15/HistogramAdjust.pdf http://homepages.inf.ed.ac.uk/rbf/HIPR2/histeqdemo.htm Books: Digital Image Processing- Rafael C. Gonzalez, Richard E. Woods, second edition, Pearson Education

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