2-1 image processing

2-1 image processing - BENG101 Foundations of Biomedical...

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BENG101 Foundations of Biomedical Imaging Fall 2009 Lecture 3: Image Processing
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Human Eye: Anatomy cones rods
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Physiologic Basis of Color Vision photoreceptors on retina rods: Scotopic vision (i.e. low light levels) Very light sensitive (can detect single photon); low acuity due to peripheral locations away from macula cones: Red, Green, Blue kinds; photopic vision (i.e. high light levels) Less sensitive but very high acuity due to being tightly packed in the macula and fovea [1]
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RGB Color Description for human, color is described by 3 primary colors, RGB mixture of light (RGB) light-producing sources: e.g. color TV & monitor “additive” primaries: Red, Green, Blue add them to produce other colors R G B
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Light Intensity perception depends on background experimentally, our eyes can distinguish few dozen grayscale (intensity) at once object (constant) background (changing)
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Sampling & Quantization spatial sampling digitizing from continuous spatial locations to discrete coordinates (e.g., M-rows × N-columns) related to image size & resolution signal intensity quantization digitizing from continuous to discrete values determines k-bit grayscale (2 k ) (e.g. 8-bit = 256 values: 0 to 255) A B A B 0 255 0 255 e.g. 32 spatial locations 256 grayscale
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Sampling & Quantization
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Spatial Sampling: Image Size & Resolution 512 2 128 2 32 2 256 2 64 2
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Color Image 3 “R,G,B channels” of grayscale images 248 248 249 245 249 242 229 224 231 225 230 242 235 243 249 250 219 221 219 210 217 208 192 184 193 185 192 208 199 212 220 223 81 82 80 63 76 56 33 21 34 20 32 57 42 66 83 90 8-bit or 0-255 grayscale; 0=black, 255=white 8-bit x 3 ch = “24”-bit image
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Histogram statistical distribution of grayscale values original image 0 5000 10000 15000 0 128 Grayscale Value # of pixels found 255
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Image is darkened 0 5000 10000 15000 0 128 Grayscale Value # of pixels found 255
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0 5000 10000 15000 0 128 Grayscale Value # of pixels found 255 Image is lightened
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Gray Scale Transformations in Medical Imaging
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Gray Scale Transformations in Medical Imaging a) Window/Level (center) operation: A window is chosen defined by level (center) and width.
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