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Cameras and Digital Imaging

Cameras and Digital Imaging. (Some of this you can actually use in everyday life). An Important Number. The wider a camera lens opening (aperture), the more light enters. The greater the distance from lens to sensor (focal length), the more light is spread out and the fainter the image

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Cameras and Digital Imaging

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  1. Cameras and Digital Imaging (Some of this you can actually use in everyday life)

  2. An Important Number • The wider a camera lens opening (aperture), the more light enters. • The greater the distance from lens to sensor (focal length), the more light is spread out and the fainter the image • If (focal length)/(aperture) is constant, the image is always the same brightness regardless of the size of the camera • (focal length)/(aperture) = f-ratio

  3. F-ratio

  4. Depth of Field

  5. Depth of Field: f/2.7

  6. Depth of Field: f/8.0

  7. Diffraction • Any time light encounters an edge (lens, mirror, opening of any kind), diffraction occurs • Diffraction limits the resolution of optical instruments • Relatively unimportant for film but much more important for digital imaging • Film is a continuous recording medium • Digital imaging involves discrete pixels

  8. Diffraction

  9. Wide Aperture Lessens Diffraction

  10. Short Focal Length Lessens Diffraction

  11. Diffraction Creates Interference

  12. All Images Are Blurry

  13. The Airy Disk

  14. Why Bright Stars Look Bigger

  15. Image Resolution • Two objects will not appear distinct unless their Airy disks are separate • Airy disk size = 2.4 x wavelength x f-ratio • 500 nm and f/4 = 5280 nm = 5.3 microns • About the size of retinal cells • Didn’t matter much for film • Does it pay to have pixels smaller than the Airy disk?

  16. Bayer RGB Filter

  17. What is a Pixel? • Digital cameras use Bayer RGB filter for color rendition • ¼ of receptors are red sensitive, ¼ are blue sensitive and ½ are green sensitive • Matches color sensitivity of eye • Four receptors (1R 2G 1B) = a pixel

  18. Super-Mega-Pixels • Pixels smaller than the Airy disk ( a few microns) contribute no resolution • Downside of mega-pixel cameras • Fewer photons per pixel = more noise • Bloated file sizes • Probably no harm • Biggest problem with tiny cameras is inferior lenses

  19. More on Megapixels • HDTV = 2 megapixels • James Cameron filmed Avatar with 2.2 megapixel cameras • Anything over 5 megapixels probably unnecessary • More pixels don’t help, but don’t hurt either

  20. Satellite Imaging • Old Old School • Shoot on film • Develop on board • Scan with oscilloscope and photocell • Reconstruct on ground • Examples • Luna III 1959 • Lunar Orbiter

  21. Luna 3, October,. 1959

  22. Lunar Orbiter, 1966

  23. Lunar Orbiter, 1967

  24. Direct Film Imaging

  25. First Weather Satellite Image(Television Imaging)

  26. Spacecraft Imaging • Photomultiplier tubes are extremely sensitive and reliable • Television-like technology used on spacecraft well into 1980’s • Galileo (launched 1989) was the first mission to use solid state imaging • 800 x 800 pixels

  27. Landsat Sensors

  28. Sensor Sweep

  29. Tornado Track and Bad Pixels

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