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Three Dimensional Visual Display Systems for Virtual Environments. Michael McKenna, David Zeltzer Presence, Vol. I, No. 4, 1992 Presenter: Dong Jeong. Purpose. Examining Five 3D display types stereoscopic, lenticular, parallax barrier, slice-staking, and holographic displays
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Three Dimensional Visual Display Systems for Virtual Environments Michael McKenna, David Zeltzer Presence, 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? a=2*atan(16.5/46) ≈ 40° b=2*atan(13/46) ≈ 32° 33cm b 26cm 46cm a 46cm
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.