Lec5 - IEG 4190 Lecture Notes 5 Lecturer Jianzhuang Liu Outline 1 2 3 4 5 6 7 8 Grayscale Modification Highpass Filtering Homomorphic Processing

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1 IEG 4190 Lecture Notes 5; Lecturer: Jianzhuang Liu Outline: 1. Grayscale Modification 2. Highpass Filtering 3. Homomorphic Processing 4. Adaptive Processing 5. Lowpass Filtering 6. Median Filtering 7. Edge Detection 8. Motion Estimation
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2 Grayscale Modification Grayscale modification: Increasing contrast of original degraded images to make them look sharper. Recording medium may not have enough dynamic range. Contrast reduction due to low light, mist, or cloud cover. Depends on applications: Gamma correction. Manual gray scale modification. Histogram modification.
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3 Grayscale Modification, cont’d Gamma correction: The electro-optical transfer characteristic of the CRT is inherently nonlinear. It is necessary to compensate for the CRT nonlinearity by introducing a compensating nonlinearity, usually referred to as gamma correction. ANSI standard: CRT: γ + = 099 . 1 ) 099 . 0 ( r T V L for 1 0812 . 0 r V 5 . 4 r T V L = f o r 0812 . 0 0 r V r V is the video signal level; T L is the light output Camera 099 . 0 099 . 1 ) / 1 ( × = C C L V for 1 0812 . 0 C L C C L V × = 500 . 4 f o r 0812 . 0 0 C L C V is the video signal output; C L is the light input, 2 . 2 = .
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4 Grayscale Modification, cont’d
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5 Grayscale Modification, cont’d Manual grayscale modification
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6 Grayscale Modification, cont’d Histogram: number of pixels as a function of image intensity.
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7 Grayscale Modification, cont’d Examples of images and their histograms
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8 Grayscale Modification, cont’d Histogram modification: Input histogram: ) ( f p Desired output histogram: ) ( g p d , typically smooth and spread out. () gT f = such that d p gp g ; T : monotonically nondecreasing. Compute the cumulative histogram: = + = = f k f p f P k p f P 0 ) ( ) 1 ( ) ( ) ( = + = = g k d d d d g p g P k p g P 0 ) ( ) 1 ( ) ( ) ( Choose the transformation so that for each f , choose g so that ) ( g P d is as close to ) ( f P as possible.
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9 Grayscale Modification, cont’d
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10 Grayscale Modification, cont’d () pf d pg ? T = M M Pf d Pg ' T ' TT Finding is not easy. Convert the problem to an easier one where finding ' is easy.
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This note was uploaded on 10/13/2009 for the course CS 5150 taught by Professor Xulei during the Spring '09 term at University of Central Arkansas.

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Lec5 - IEG 4190 Lecture Notes 5 Lecturer Jianzhuang Liu Outline 1 2 3 4 5 6 7 8 Grayscale Modification Highpass Filtering Homomorphic Processing

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