Three Dimensional Visual Display Systems for Virtual Environments

1
Three Dimensional Visual Display Systems for
Virtual Environments

• Michael McKenna, David Zeltzer
• Presence, Vol. I, No. 4, 1992
• Presenter Dong Jeong

2
Purpose

• Examining
• Five 3D display types
• stereoscopic, lenticular, parallax barrier,
  slice-staking, and holographic displays
• Characteristics of each display type
• Spatial resolution, depth resolution, filed of
  view,, viewing zone, bandwidth, etc.
• Comparison
• Comparing different display systems and the human
  visual system in tabular form

3
Criteria for Display Systems

• A set of criteria
• Developed to compare different types of display
  systems
• Visual Cues and Display Attributes
• Field of View, Spatial Resolution, Refresh and
  Update Rates, Brightness, Color, Information Rate
  and Bandwidth, Viewing Zone/ Volume Extent, and
  Number of Views
• Depth Perception and Depth Cues
• Autostereoscopy, Oculomotor Cues, Binocular
  Disparity, Motion Parallax, Pictorial Depth Cues,
  Viewing Situations and Depth Cues

4
Visual Cues and Display Attributes

• Field of View, Spatial Resolution, Refresh and
  Update Rates, Brightness, Color, Information Rate
  and Bandwidth, Viewing Zone/ Volume Extent, and
  Number of Views

5
Field of View I

• The angle subtended by the viewing surface from a
  given observer location.
• For human 120 vertical and horizontal,
  Approximately 180 horizontal (both eyes)

6
Field of View II

• Example
• A typical workstation display 33x26cm
• A comfortable viewing distance 46cm
• Horizontal x vertical FOV?

a2atan(16.5/46) 40 b2atan(13/46) 32
33cm
b
26cm
46cm
a
46cm
7
Spatial Resolution

• Common measurement of 2D displays
• Resolution is typically measured by the number of
  pixels. Pixel is measured as pitch.
• Foveal FOV
• Measuring the visual acuity, or the spatial
  resolution of the eye
• For normal human subjects,
• The smallest visual target can be perceived 50
  of the time is approximately 1min to 30 sec of
  arc.

8
Refresh and Update Rates I

• Displaying stable images
• Need to repeatedly redraw or refresh
• Refresh rate
• The frequency at which a display redraws its
  imagery
• Critical fusion frequency (CFF)
• The threshold above which a refreshed image
  appears steady.
• Dependent on a number of factors, the brightness
  of the display, the ambient illumination, and the
  size and location in the visual field of the
  stimlus.
• For most applications, 60Hz flicker-free

9
Refresh and Update Rates II

• Update rate
• The frequency at which the computer modifies, or
  updates, the displayed imagery.
• Drops below 10-15 Hz, motion will appear
  discontinuous and become distracting.

10
Brightness

• CRT and other displays
• Limited in the range of brightness levels.
• The displayed intensity levels are usually
  nonlinear to the control signal and framebuffer.
• The overall brightness of a display strongly
  affects the visual tasks. It also influences
  visual acuity and color perception.

11
Color

• No display can match the range of colors visible
  to the healthy human eye.
• If we have means of stimulating the three kinds
  of cone cells (red, yellow-green, blue
  wavelengths), reproducing the color sensations is
  possible. trichromatic color reproduction.
• Monochrome (one),
• Beam penetration monitors (two)
• useful for flight simulators generating only
  night scenes.

12
Information Rate and Bandwidth

• Information Rate
• What rate of data (bits/sec) is needed to drive a
  display.
• 4.5Mbits/sec for the two eyes (single nerve 5
  bits/sec)
• Very low information rate. But only
  high-resolution in the foveal region.
• Bandwidth
• The maximum rate at which the signal (pixel
  values) can change. Highest frequency signal.

13
Viewing Zone/ Volume Extent

• Viewing Zone
• Angular range over which the displayed imagery
  can be perceived.
• Viewing volume
• Limited in the nearest and furthest locations in
  where images can be displayed.

14
Number of Views

• Limited number of distinct views
• Also limitation is existed depending on the
  technology used.
• In general, the more views which are imaged, the
  greater the bandwidth required.

15
Depth Perception and Depth Cues

• Autostereoscopy, Oculomotor Cues, Binocular
  Disparity, Motion Parallax, Pictorial Depth Cues,
  Viewing Situations and Depth Cues

16
Autostereoscopy

• Do not require special viewing aids
• Polarized glasses or a stereoscope
• Depending on the size of the viewing zone or
  viewing volume, images can be seen by multiple
  viewers.

17
Oculomotor cues

• Physiological cues based on our ability to sense
  the tension in the muscles that control eye
  movement and lens focus.
• Accomodation
• The angular muscles in the eye relax and contract
  to change the shape of the lens.
• Effective only at distances less than 2 m.
• Convergence
• When fixating on an object, the eyes rotate to
  center their viewing axes on a particular point
  in space.
• Effective up to approximately 10 m.

18
Binocular Disparity

• The difference in the retinal images that is due
  to the projection of object points at different
  depths.
• Can be analyzed through the convergence angles.
• Stereopsis
• Depth perception due to binocular disparity

19
Motion Parallax

• Monocular cue that is generated as the viewpoint
  of the observer changes.
• Can be defined as the differential angular
  velocity of objects at different depths from the
  observer.

20
Pictorial Depth Cues

• Overlap
• Image size
• Linear perspective
• Texture gradient
• Aerial perspective
• Shading

21
Viewing Situations and Depth Cues I

• At medium to far distances (over 10 m),
  accommodation and convergence are in effective.
• At near distances, binocular disparity is a very
  important depth cue.
• At great distances, disparity becomes less
  important.
• In complex or unfamiliar scenes, binocular
  disparity helps.
• Binocular disparity also improves apparent image
  quality. (useful when low bandwidth or noisy
  signals are used)
• A wider total field of view can be created when
  two separate image sources are used.
• Off-road driving, binocular disparity is
  important to enhance the perception of the
  driving-surface slope.

22
Viewing Situations and Depth Cues II

• With still 2D imagery, the pictorial cues are the
  only cues to depth.
• When only monocular images are available, motion
  parallax is an important cue.
• Aerial perspective is important when realistic
  conditions for long-distance viewing are
  required.
• Fog and haze are also useful depth cues.
• For flight simulators, realistic texturing of the
  ground surface, motion parallax, etc are
  important.

23
Three-Dimensional Display Systems

• Examine five 3D display systems
• Stereoscopic, lenticular, parallax barrier,
  slice-staking, and holographic video.

24
Stereoscopic Display I

• Special viewer or filtering glasses are used.
• PLZT or LCD shutter glasses alternately block
  each eyes view of the screen.

25
Stereoscopic Display II

• Infinity optics
• Infinity optics collimate the light emitted from
  each point in the image, so that they form
  parallel rays.
• Lens or mirror systems are often used to enlarge
  small monitors.
• Preferred in flight simulators

26
Stereoscopic Display III

• Spatial resolution and Field of view

27
Stereoscopic Display IV

• Displays with a finite spatial resolution
• Limitation on the number of discrete depth spots
  that can be imaged. (because of a sampling effect)

28
Stereoscopic Display V

• There is a limit on the minimum separation of
  depth points that can be imaged by a stereo pair
  with finite-sized image elements.

29
Stereoscopic Display VI

• Refresh Rate Need to be above 60 Hz (each
  monitors)
• Brightness The brightness to each eye is reduced
  because of filtering glassess.
• Color RGB
• Information Rate and Bandwidth Similar to 2D
  displays
• Viewing Zone Extent limited to the regions with
  a clear view of the display screen.
• Number of Views one stereographic 3D view
  composed of two 2D images.