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? 26cm 46cm b a 33cm 46cm a=2*atan(16.5/46) ≈ 40° b=2*atan(13/46) ≈ 32°

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 eye’s 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.