ece542-3 - ECE542-3 Digital Image Processing Image...

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1 Digital Image Processing ECE542-3 3- Image Enhancement in the Spatial Domain Dr. Z. Aliyazicioglu Cal Poly Pomona Electrical & Computer Engineering 1 Cal Poly Pomona Electrical & Computer Engineering Office 9-143 Principle Objective Process an image so that the result will be more suitable than the original image for a specific application. A method which is quite useful for enhancing an image may not necessarily be the best approach for enhancing another images Spatial Domain : (image plane) Techniques are based on direct manipulation of pixels in an image Frequency Domain : Techniques are based on modifying the Fourier transform of an ECE542-3 2 Cal Poly Pomona Techniques are based on modifying the Fourier transform of an image There are some enhancement techniques based on various combinations of methods from these two categories.
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2 Background Spatial domain methods are procedures that operate directly on pixels. where   (, ) gxy Tfxy where f(x,y) is the input image g(x,y) is the processed image T is an operator on f defined over some neighborhood of (x,y) Neighborhood = 1x1 pixel g depends on only the value of f at (x,y) T = gray leve (or intensity or mapping) ECE542-3 3 Cal Poly Pomona = gray level (or intensity or mapping) transformation function where r = gray level of f(x,y) s = gray level of g(x,y)   sT r Contrast Stretching and Thresholding Contrast Stretching: Produce higher contrast than the original by darkening the levels below m in the original image darkening the levels below Brightening the levels above m in the original image Thresholding function: Produce a two-level (binary) image ECE542-3 4 Cal Poly Pomona
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3 Mask Processing or Filter Neighborhood is bigger than 1x1 pixel Use a function of the values of f in a predefined neighborhood of ( x , y ) to determine the value of g at ( x , y ) Basically, a mask is a small (3x3) 2-D array. The value of the mask coefficients determine the nature of the process Used in techniques Image Sharpening ECE542-3 5 Cal Poly Pomona Image Sharpening Image Smoothing Basic gray-level transformation Linear function Negative and identity transformations Logarithm function Log and inverse-log transformation Power-law function n th power and n th root transformations ECE542-3 6 Cal Poly Pomona 8 bit environment level has 0 to 255 values
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4 Image Negatives An image with gray level in the range [ 0, L-1 ] where L = 2 n ; n = 1 2 where L 2 ; = 1, 2,… (n:number of bits) Negative transformation : s = L – 1 –r Reversing the intensity levels of an image.
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This note was uploaded on 10/24/2010 for the course ECE 542 taught by Professor Zeki during the Spring '10 term at Cal Poly Pomona.

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ece542-3 - ECE542-3 Digital Image Processing Image...

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