Fundamentals of Image Processing A Seminar on By Alok K. Watve 20 November 2018

Applications of image processing Gamma ray imaging X-ray imaging Multimedia systems Satellite imagery Flaw detection and quality control And many more……. 20 November 2018

Fundamental Steps in digital image processing Image acquisition Image enhancement(gray or color images) Wavelet and multi-resolution processing Compression Morphological processing Segmentation Representation & description Object recognition Low level processing Medium level processing High level processing 20 November 2018

Image enhancement in spatial domain Binary images Only two colors Gray images A range of colors(not more than 256) from black to white Color images Contain several colors(as many as 224) 20 November 2018

Image : A 2D function represented by I = f(x,y) Definitions Image : A 2D function represented by I = f(x,y) where I = intensity of the point(x,y) Foreground : Objects of interest in an image Background : Everything that’s not in foreground 20 November 2018

freq(I) = # pixels with intensity I Definitions Histogram : A graph of frequency(of an intensity) versus intensity. Frequency is expressed as count of pixels freq(I) = # pixels with intensity I Spatial resolution : Smallest discernible detail in the image. Depends on the sampling. Gray-level resolution : smallest discernible change in the gray level change. 20 November 2018

Basic gray level transformations Image negatives s = (L – 1) – r Where, s = output intensity* r = input intensity* (L – 1) = Maximum intensity* *These notations will be used throughout the seminar 20 November 2018

Basic gray level transformations Original image Negative image 20 November 2018 All images: courtesy : www.imageprocessingplace.com

Basic gray level transformations Power law transformation s = c. rγ Here, c is a constant 20 November 2018

Basic gray level transformations Original image Transformed image (c = 1, γ = 0.3) 20 November 2018

Basic gray level transformations Contrast stretching : increases dynamic range L-1 S2 Output intensity S1 0, 0 L1 L2 L-1 Input intensity 20 November 2018

Basic gray level transformations Original image Image obtained by contrast stretching 20 November 2018

Basic gray level transformations Bit plane slicing 20 November 2018

Basic gray level transformations 20 November 2018

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Basic gray level transformations Histogram equalization Image of mars’ moon histogram 20 November 2018

Basic gray level transformations Histogram equalization transformation can be expressed as a monotonically increasing function with domain and range = [0, 1]** Assuming the intensities are normalized in the range [0,1] 20 November 2018

Basic gray level transformations A low contrast image and its histogram 20 November 2018

Basic gray level transformations Result of histogram equalization 20 November 2018

Filtering in spatial domain Concept of frequency Modeling filters using convolution in spatial domain Implementing filters using masks 20 November 2018

g(x, y) = Σs Σt w(s, t).f(x+s,y+t) 20 November 2018

Filtering in spatial domain w(-1,-1) w(-1, 0) w(-1, 1) w(0,-1) w(0, 0) w(0, 1) f(x-1,y-1) f(x-1, y) f(x-1, y+1) w(1,-1) w(1, 0) w(1, 1) f(x,y-1) f(x, y) f(x, y+1) f(x+1,y-1) f(x+1, y) f(x+1, y+1) 20 November 2018

Averaging filter Weighted average filter Low pass filter Averaging filter Weighted average filter 20 November 2018

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A noisy image Filtered image Median filter A noisy image Filtered image 20 November 2018

Computing gradients in spatial domain Laplacian filter High pass filter Computing gradients in spatial domain Laplacian filter Other masks (operators) Roberts Sobel 20 November 2018

Designing high pass filters Method 1 g(x, y) = f(x, y) + fhp(x, y) g(x, y) = f(x, y) – flp(x, y) 20 November 2018

Laplacian operators 0 -1 0 -1 -1 -1 -1 5 -1 -1 9 -1 0 -1 0 -1 -1 -1 0 -1 0 -1 -1 -1 -1 5 -1 -1 9 -1 0 -1 0 -1 -1 -1 20 November 2018

Sobel Operators -1 -2 -1 -1 0 1 0 0 0 -2 0 2 1 2 1 -1 0 1 -1 -2 -1 -1 0 1 0 0 0 -2 0 2 1 2 1 -1 0 1 20 November 2018

Roberts cross gradient operators - 1 0 0 -1 0 1 1 0 20 November 2018

High pass filter 20 November 2018

To be contd…. 20 November 2018

Digital image processing, second edition - R. C. Gonzalez, R. E. Woods References Digital image processing, second edition - R. C. Gonzalez, R. E. Woods Fundamental of digital image processing – A. K. Jain www.imageprocessingplace.com 20 November 2018