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What’s on page 13-25?

What’s on page 13-25?. Tom Butkiewicz. Refresh Rates. Flicker from shutter systems Halve refresh rates 2 eyed 120Hz != 1 eyed 60Hz Phosphors 2 Polarized Monitors + Half Silvered Monitor. Brightness. Filter glasses remove frequencies dim images Shutter glasses

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What’s on page 13-25?

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  1. What’s on page 13-25? Tom Butkiewicz

  2. Refresh Rates • Flicker from shutter systems • Halve refresh rates • 2 eyed 120Hz != 1 eyed 60Hz • Phosphors • 2 Polarized Monitors + Half Silvered Monitor

  3. Brightness • Filter glasses • remove frequencies • dim images • Shutter glasses • Brightness halved over time • Never 100% clear (shutter and polarized)

  4. Example • Hypothetical stereoscopic display • Standard CRT • LCD shutter glasses

  5. Spatial resolution • Res = 1280 x 1024 • Shutter cut vertical in half • Res = 1280 x 512 • Angular resolution • “comfortable viewing distance” = 18 inches • Screen size = 33” x 26” • Φ = 1.9 min x 3.8 min = 1.9’ x 3.8’ • Pixel Pitch • Pitch = (33cm/1280) = (26cm/1024) = .025cm/pixel

  6. Field of view • FOV = 40° x 32° • Depth resolution • (0.00025 x 0.46) / (0.65 – 0.00025) = 0.0018m • Refresh rate: • 120Hz refresh rate = 60Hz per eye • Brightness: • LCD shutter transmits 30% of light • Screen seen 50% of the time • Overall: brightness = 15%

  7. Interactive Stereoscopic Display • Autostereoscopic displays: • Advantages: • No viewing aids required • Multiple 3D views of the scene • Interactive systems can achieve this viewpoint-dependence • Head Tracking (HMDs and HTDs)

  8. Example • Same system as before • Add head tracking • Interactive • Motion parallax • Head / Boom system

  9. Same typical monitor • 1280x1024 • Special optics • 90° field of view for each eye • Partially overlapping • FOV = 135° x 90° • Φ = 90° / 1280 = 4.2’ = 0.0012 radians • Coarse resolution • Easily change optics to suit different tasks • FOV vs Angular Resolution

  10. Depth resolution • Must calculate the pitch for infinite-focus screen at 46cm: • Pitch = 0.0012 x 46cm = 0.056 cm • D = (0.00056 x 0.46) / (0.065 – 0.00056) = 0.0040 m

  11. Lenticular Screen • Array of cylindrical lenses • Generates autostereo image • Directs 2D images into viewing subzones • Viewer puts one eye in each subzone

  12. Lenticular Screen • Horizontal resolution -> one pixel per lenticule • Vertical resolution -> same as back screen • N subzones created by N pixels behind each lenticule

  13. Side-Lobes are duplicate sub-zones off to the side of the main centered viewing zone. Moving out of viewing zone into side-lobes causes pseudoscopic 3D image (right <-> left)

  14. Limitations • High horizontal resolution required • Pixel size limits number of views • Imperfections in lenses focusing abilities • Reduces the directivity • Emerging rays not parallel • Need to have back screen perfectly aligned with lenticules • Hard because CRTs not flat

  15. Can be used with multiple projectors • Diffusing screen • High horizontal resolution and large number of views possible • High bandwidth costs

  16. Integral photography • Similar to lenticular imaging • Small spherical lenses instead of vertical cylinders • Up and down in addition to left and right • Requires more resolution or 2D array of projectors

  17. Example • Horizontal resolution • Res of each view = screen width / lenticle width = horizontal res of back screen / number of views • Horizontal angular resolution = lenticule width / Dscreen

  18. Depth Resolution • Finite size of horizontal imaging elements • Limits resolvable depth levels

  19. Depth Resolution • Subzones may overlap • Due to imperfect direction from lenses • Can degrade depth resolution • Since image space quantized depth res not degrade until blur angle approaches the angle of the viewing subzones

  20. Depth resolution • To avoid loss of resolution: • αc is the spread due to min electron beam width / focal length of lenticules • αd = 2 asin λ(wavelenght) / pitch

  21. Brightness + Color • Lenticular screens offer comparatively good brightness to other methods such as parallax barriers. • Directs only a fraction of the screen, but collects light from a larger area. • Color can be problem because of CRT phosphor layouts.

  22. Example • Similar to Hamasaki’s using Braun tube • Allows accurate registration of vertical pixel strips • 8 views • 256 x 256 each • 1 mm lenticules • Focal length 2.25 mm • Horizontal pitch .125 mm • Min electron beam size 0.07 mm • Subzones 35 – 40 mm wide at 750 mm distance

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