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 III

• Spatial resolution and Field of view

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.