Histogram Equalization of Grey Scale Images Histogram equalization

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-Non. Commercial-Share. Alike 2. 5 India license

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

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 2 an image. • Calculate the Cumulative Distribution Function (CDF) of the image using formula: 3 4 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]. 5

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

1 Step 1: 2 3 4 5 Instruction for the animator Text to be displayed in the working area (DT) • The first fig. should appear • The low contrast image • After start button is clicked show the second figure • The resulting image is the equalized image • At the same time show the graphs also (as shown in next slide) • The text in DT should appear in parallel to the figures

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

Electrical Engineering Slide 1 Introduction Slide 3 Definitions Slide 10, 11, 12 Analogy Slide 13 Want to know more… Test your understanding Lets Sum up (summary) (Further Reading) (questionnaire) Interactivity: Try it yourself Ø Select any one of the figures a b c d Ø Select the filter size 7 Credits

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

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

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

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

1 Questionnaire 3. 2 What is the equalized histogram for the image shown? 3 Answers: a) 8 No. of 7 pixels 6 4 5 4 3 2 1 5 0 63. 75 Gray level intensity 127. 5 191. 25 255

1 Questionnaire 3. Question 3 cont’d. . . 2 What is the equalized histogram for the image shown? 3 Answers: b) 8 No. of 7 pixels 6 4 5 4 3 2 1 5 0 63. 75 Gray level intensity 127. 5 191. 25 255

1 Questionnaire 3. Question 3 cont’d. . . 2 What is the equalized histogram for the image shown? 3 Answers: c) 8 No. of 7 pixels 6 4 5 4 3 2 1 5 0 63. 75 Gray level intensity 127. 5 191. 25 255

1 Questionnaire 3. Question 3 cont’d. . . 2 What is the equalized histogram for the image shown? 3 Answers: d) 8 No. of 7 pixels 6 4 5 4 3 2 1 5 0 63. 75 Gray level intensity 127. 5 191. 25 255

Links for further reading Reference websites: http: //en. wikipedia. org/wiki/Histogram_equalization http: //math. uci. edu/icamp/courses/math 77 c/demos/hist_eq. pdf http: //nature. berkeley. edu/~bingxu/UU/spatial/Week 15/Histogram. Adjust. pdf http: //homepages. inf. ed. ac. uk/rbf/HIPR 2/histeqdemo. htm Books: Digital Image Processing. Rafael C. Gonzalez, Richard E. Woods, second edition, Pearson Education