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Image Processing Basics: Understanding Digital Images and Operations

Explore the fundamentals of image processing, including the definition of an image, digital representation, histogram-based enhancement, edge detection, and noise filtering techniques.

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Image Processing Basics: Understanding Digital Images and Operations

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  1. IMAGE PROCESSING AKSHAY P S3 EC ROLL NO. 9

  2. What is an image? • We can think of an image as a function, f, from R2 to R: • f( x, y ) gives the intensity at position ( x, y ) • Realistically, we expect the image only to be defined over a rectangle, with a finite range: • f: [a,b]x[c,d]  [0,1] • A color image is just three functions pasted together. We can write this as a “vector-valued” function:

  3. What is a digital image? • We usually operate on digital (discrete)images: • Sample the 2D space on a regular grid • Quantize each sample (round to nearest integer) • If our samples are D apart, we can write this as: f[i ,j] = Quantize{ f(iD, jD) } • The image can now be represented as a matrix of integer values

  4. Image processing • An image processing operation typically defines a new image g in terms of an existing image f. • We can transform either the range of f. • Or the domain of f:

  5. Histogram based Enhancement Histogram of an image represents the relative frequency of occurrence of various gray levels in the image MATLAB function >imhist(x)

  6. Why Histogram? It is a baby in the cradle! Histogram information reveals that image is under-exposed

  7. Histogram Equalization Uniform Quantization Note: y cumulative probability function L 1 x L 0 Image processing

  8. Image Example after before

  9. The Sobel Edge Detector The Sobel operator, sometimes called the Sobel–Feldman operator or Sobel filter, is used in image processing and computer vision, particularly within edge detection algorithms where it creates an image emphasising edges. 9

  10. The Canny Method • Canny is a more effective method than sobel. Its input is output of sobel. • It produces finer edges than sobel • After finding gradient using sobel method,canny uses a method called Hysterisis thresholding to remove anomalities due to noise.

  11. Image noise Original image White Gaussian noise Salt and pepper noise (each pixel has some chance of being switched to zero or one)

  12. Median filtering • A median filter operates over a window by selecting the median intensity in the window

  13. Median filter • What advantage does median filtering have over mean filtering?

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