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Understanding Refresh Rates and Stereoscopic Display Technologies

This text explores the complexities of refresh rates in stereoscopic displays, comparing 120Hz to 60Hz systems. It discusses the impact of shutter glasses on brightness and clarity, highlighting phenomena like flicker and dimming over time. The document also addresses geometric considerations such as spatial resolution and pixel pitch, along with the principles of autostereoscopic displays and the limitations of lenticular screens. Detailed examples illustrate the relationships between resolution, depth perception, and image quality in various display technologies.

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Understanding Refresh Rates and Stereoscopic Display Technologies

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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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