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Digital Image Processing

Digital Image Processing

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Digital Image Processing

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  1. Digital Image Processing

  2. Last discussed topics • Image Processing Introduction • Digital Image Creation • Image Types • Image File Formats

  3. Agenda • Types of digital image processing • Brightness • Complement • Image histogram • Image types conversion

  4. General Areas of Image Processing • 3 general areas of digital image processing • Point Operations • Pixel Point Processing • Local Operations • Pixel Group Processing • Global Operations

  5. Basics of Digital Images (review) • Digital images are a 2D array of values in rows and columns given by I(r,c)

  6. Point Operations • A point operation operates on individual pixels and does not take into account any neighbouring pixel values • The same operation occurs on all of the pixels in the image

  7. Point Operation Process I(x,y) Operation x 1.5 O(x,y)

  8. Clipping • Clipping results from an operation (any) on an image where the pixel value that result from the operation exceeds the limits of the bit depth of the image eg. in an 8 bit depth image • operation = x2, pixel value = 150, new (output) value = 300 is clipped to 255 • operation = -50, pixel value = 10, new (output) value = -40 is clipped to 0

  9. Arithmetic operations (Brightness) Simple functions include adding or subtract a constant value to each pixel: Or Multiplying a constant value to each pixel: In order to ensure that the output value ranges from 0 to 255 you have to: Round the output values to an integer values Clipping the output value to ranges from 0 to 255

  10. Adding and subtracting a constant We can test this on the blocks image blocks.tif Original Image

  11. Using multiplication and division Original Image

  12. Complements (Negative) Original Image

  13. Image Histogram • a graph indicating the number of times each grey level occurs in the image • Provides • an indication of distribution of pixels values • an indication for image contrast & brightness • Can be used to aid in adjustment of image contrast levels and brightness • Does not provide any information about what can be perceived within the image, i.e. does not provided any spatial information

  14. Image Histogram Cont. Image Histgram Original image with 3 gray levels Digital Image Array

  15. Image Histogram No. of pixels Pixel values Image Histogram: Plot of pixel values v and no of pixels with that value

  16. Image Contrast: - well balanced

  17. High Image Contrast Low Image Contrast

  18. Low Image Contrast Low Image Contrast

  19. How to Convert from Grayscscale to Binary Image Gray Image Binary Image

  20. How to Convert from RGB to Grayscale Image RGB Image Gray Image

  21. How to Convert from RGB to Grayscale Image • Solution 1 • Solution 2 Choose one of R or G or B to represent the Gray image