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Point Processing

Learn about the significance of dynamic range in image formation and how point processing techniques can enhance image quality. Explore power-law transformations, contrast stretching, histogram equalization, and color transfer methods.

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Point Processing

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  1. Point Processing • CS194: Image Manipulation & Computational Photography • Alexei Efros, UC Berkeley, Fall 2017

  2. Image Formation • f(x,y) = reflectance(x,y) * illumination(x,y) • Reflectance in [0,1], illumination in [0,inf]

  3. Problem: Dynamic Range • The real world is • High dynamic range • 1 • 1500 • 25,000 • 400,000 • 2,000,000,000

  4. Long Exposure • 10-6 • 106 • High dynamic range • Real world • 10-6 • 106 • Picture • 0 to 255

  5. Short Exposure • 10-6 • 106 • High dynamic range • Real world • 10-6 • 106 • Picture • 0 to 255

  6. ò Image Acquisition Pipeline Lens Shutter scene radiance (W/sr/m ) sensor irradiance sensor exposure 2 Dt • CCD • ADC • Remapping • analog • voltages • digital • values • pixel • values

  7. Simple Point Processing: Enhancement

  8. Power-law transformations

  9. Basic Point Processing

  10. Negative

  11. Log

  12. Contrast Stretching

  13. Image Histograms • Cumulative Histograms • s = T(r)

  14. Histogram Equalization

  15. Color Transfer [Reinhard, et al, 2001] • Erik Reinhard, Michael Ashikhmin, Bruce Gooch, Peter Shirley, ColorTransfer between Images. IEEE Computer Graphics and Applications, 21(5), pp. 34–41. September 2001.

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