three dimensional visual display systems for virtual environments michael mckenna, david zeltzer...
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Three Dimensional Visual Display Systems for Virtual Environments
Michael McKenna, David ZeltzerPresence, Vol. I, No. 4, 1992
Presenter: Dong Jeong
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
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
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
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)
Field of View II
• Example– A typical workstation display: 33x26cm– A comfortable viewing distance: 46cm– Horizontal x vertical FOV?
26cm
46cm
b
a
33cm
46cm
a=2*atan(16.5/46) ≈ 40°
b=2*atan(13/46) ≈ 32°
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.
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
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.
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.
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.
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.
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.
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.
Depth Perception and Depth Cues
• Autostereoscopy, Oculomotor Cues, Binocular Disparity, Motion Parallax, Pictorial Depth Cues, Viewing Situations and Depth Cues
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.
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.
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
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.
Pictorial Depth Cues
• Overlap
• Image size
• Linear perspective
• Texture gradient
• Aerial perspective
• Shading
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.
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.
Three-Dimensional Display Systems
• Examine five 3D display systems– Stereoscopic, lenticular, parallax barrier, slice-
staking, and holographic video.
Stereoscopic Display I
• Special viewer or filtering glasses are used.– PLZT or LCD shutter glasses alternately block
each eye’s view of the screen.
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
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)
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.
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.