Three Dimensional Visual Display Systems for Virtual Environments

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Three Dimensional Visual Display Systems for
Virtual Environments
Part 3

• Presented by Evan Suma

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Parallax Barrier

• Vertical slit plate
• Blocks part of the screen from each eye
• Screen displays images in vertical strips

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Parallax Barrier

• More than two images can be displayed
• Creates multiple views from side to side

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Parallax Barrier

• Horizontal res display res / of 2D views

Multiple projecting monitors can be used to
maintain higher horizontal resolution.
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Parallax Barrier Drawbacks

• Not commonly used
• Barrier blocks most of light to eye
• Causes dim image
• Small slit widths can result in diffraction of
  spreading light rays

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Parallax Barrier Diffraction

• Angular spread of light through slit of width a
  is approximatelywhere ? is the wavelength of
  light passing through the slit

? 2 asin ( ? / a )
a pitchslit / N
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Parallax Barrier Diffraction

• More diffraction than lenticular display
• Caused by loss of directivity of barrier
• Parallax barrier is only a fraction of lenticular
  pitch

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Parallax Barrier Brightness

• Reduce light which reaches eye
• where B0 is brightness of unblocked screen

Brightness B0 ( a / pitchslit )
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Parallax Barrier Rate and Bandwidth

• Horizontal resolution is reduced(same as
  lenticular displays)
• Bandwidth must be increased to maintain high
  visible resolution
• Or sacrifice other parameter
• Vertical resolution
• Refresh rate

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Parallax Barrier Rate and Bandwidth

• Horizontal resolution is reduced(same as
  lenticular displays)
• Bandwidth must be increased to maintain high
  visible resolution
• Or sacrifice other parameter
• Vertical resolution
• Refresh rate

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Slice Stacking

• Building a 3D volume by layer 2D images
• Also called multiplanar displays
• Rather than use a planar mirror, a variable-focus
  mirror can be used

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Slice Stacking

• Common method uses acoustics
• Vibrates a reflective membrane
• Causes focal length to change
• Uses reflection from monitor
• Over time forms a truncated-pyramid viewing volume

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Slice Stacking

• Traces out a luminous volume
• Objects are transparent
• Objects further in depth cannot be obscured

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Slice Stacking

• Ideal for volumetric data sets and modeling
  problems
• Poorly suited to photographic or realistic
  images with hidden surfaces

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Slice Stacking Resolution and FOV

• Spatial resolution and FOV the same as underlying
  2D display
• Varifocal mirrors limited to approximately 20
  inches due to acoustic and mirror characteristics

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Slice Stacking Depth Resolution

• Depth of reflected CRT is constantly changing
• Very fine resolution of depth spots can
  potentially be imaged
• Limited by bandwidth of CRT and persistence of
  phosphors

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Slice Stacking Accommodation

• One of the few displays that support ocular
  accommodation
• Actually displays points in 3D space either
  directly or optically

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Slice Stacking Refresh Rate

• Refresh rate is twice frequency of vibration
• Typically 30 Hz signal drives mirror
• Results in 60 Hz refresh rate

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Slice Stacking Brightness

• Short persistence phosphors must be used
• Prevents smearing of image in depth
• Brightness somewhat reduced from typical 2D
  display
• Phosphors of short enough duration only available
  in green (circa 1986)

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Slice Stacking Viewing Zone

• Viewing zone limited by position of display CRT
• Obstructs viewing zone
• Can use beam splitter to move CRT below, but
  lowers brightness by at least 75

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Slice Stacking Viewing Volume

• Magnification of mirror changes size of reflected
  CRT
• Results in truncated pyramid volume instead of
  rectangle

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Slice Stacking Volume Extent

• Mirrors have leverage of approximately 85
• Distance h in mirror
• Movement 85h in reflected image

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Slice Stacking Number of Views

• Number of views essentially unlimited
• Horizontal and vertical parallax are both
  supported

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Holography CG Stereograms

• Recorded optically from a set of 2D views of a 3D
  scene
• Projects each 2D image into a viewing zone
• Stereo views with horizontal parallax
• Full-color, high resolution images
• Non-real time
• Requires a huge amount of information (100-300
  views)

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Holography CG diffraction patterns

• Generates a diffraction pattern
• Hologram creates a 3D wavefront when illuminated
• Images 3D objects and light sources in space
• Traditional methods were complex and
  computationally expensive
• New method (circa 1992) allows generation to be
  displayed in real-time

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Holography Spatial Resolution

• Very high horizontal resolution is needed
• Vertical resolution can be lower
• High horizontal resolution is not resolution of
  displayed holographic image
• Horizontal resolution of image points is
  diffraction limited
• Beyond human perceptual limits

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Holography Miscellaneous

• Like slice-stacking displays, holograms support
  ocular accommodation
• Good brightness and contrast using low-power
  laser (a few milliwatts)
• Both monochromatic and color have been
  demonstrated
• Very high bandwidth compared to other systems

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Holography Miscellaneous

• Depth resolution is beyond human perceptual
  capabilities
• Provides many views from side-to-side
• No vertical parallax
• Viewing zone angle is determined by the frequency
  of diffraction pattern
• MIT systems depth range limited to approximately
  100mm
• MIT systems refresh rate is 36 Hz with a little
  flicker

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Any Questions?