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BME5002 Image Processing Lecture 1 John G. Harris 1/26/01

BME5002 Image Processing Lecture 1 John G. Harris 1/26/01. Image Processing Goals. Improve image quality Image enhancement Feature extraction Computer-aided diagnosis Required for image formation for some modalities (CT, MRI, etc.). Aspects of Image Quality. Contrast vs. dynamic range

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BME5002 Image Processing Lecture 1 John G. Harris 1/26/01

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  1. BME5002Image Processing Lecture 1John G. Harris 1/26/01

  2. Image Processing Goals • Improve image quality • Image enhancement • Feature extraction • Computer-aided diagnosis • Required for image formation for some modalities (CT, MRI, etc.)

  3. Aspects of Image Quality • Contrast vs. dynamic range • Blur • Noise

  4. Contrast vs. Dynamic Range

  5. Characteristic Film Curve 3 shoulder 2 OPTICAL DENSITY base + fog 1 toe 0 LOG(EXPOSURE)

  6. 4 Major Causes of Blur FOCAL SPOT BODY SCREEN FILM

  7. Diffusion of Light in Screen

  8. Film Characteristics 0.8 LOG( EXPOSURE TIME) BLUR (mm) 0.4 0.2 0.1 50 100 200 400 800 FILM SPEED

  9. Methods to Reduce Blur • Smaller focal spot • Thinner Screens • Place film farther away • Slower film

  10. Range of Blur Values • 0.5mm for normal radiographs • 0.15mm for mammograms BLUR

  11. Noise • Quantum noise in body, screen, film • Nonuniformity of film Noise reduces visibility of low contrast features

  12. Quantum Noise • Standard deviation of noise is proportional to the square root of the number of photons • Therefore the effect of quantum noise can be reduced by increasing the exposure (intensity x time).

  13. Blur vs. Noise Tradeoff X-rays screen sensitive film film image MORE NOISE MORE BLUR

  14. Can Reduce Quantum Noise • More intensity • More exposure time • Thicker screen • More efficiency in screen • All of the above require less sensitive film

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