1. Three Dimensional Visual Display Systems for Virtual Environments Presented by Evan Suma Part 3

2. Parallax Barrier Vertical slit plate Blocks part of the screen from each eye Screen displays images in vertical strips

3. Parallax Barrier More than two images can be displayed Creates multiple views from side to side

4. Parallax Barrier Horizontal res = display res / # of 2D views Multiple projecting monitors can be used to maintain higher horizontal resolution.

5. Parallax Barrier: Drawbacks Not commonly used Barrier blocks most of light to eye Causes dim image Small slit widths can result in diffraction of spreading light rays

6. Parallax Barrier: Diffraction Angular spread of light through slit of width α is approximately where λ is the wavelength of light passing through the slit θ = 2 asin ( λ / α ) α = pitch slit / N

7. Parallax Barrier: Diffraction More diffraction than lenticular display Caused by loss of directivity of barrier Parallax barrier is only a fraction of lenticular pitch

8. Parallax Barrier: Brightness Reduce light which reaches eye where B 0 is brightness of unblocked screen Brightness = B 0 * ( α / pitch slit )

9. Parallax Barrier: Rate and Bandwidth Horizontal resolution is reduced (same as lenticular displays) Bandwidth must be increased to maintain high visible resolution Or sacrifice other parameter –Vertical resolution –Refresh rate

10. Parallax Barrier: Rate and Bandwidth Horizontal resolution is reduced (same as lenticular displays) Bandwidth must be increased to maintain high visible resolution Or sacrifice other parameter –Vertical resolution –Refresh rate

11. Slice Stacking Building a 3D volume by layer 2D images Also called multiplanar displays Rather than use a planar mirror, a variable- focus mirror can be used

12. Slice Stacking Common method uses acoustics Vibrates a reflective membrane Causes focal length to change Uses reflection from monitor Over time forms a truncated- pyramid viewing volume

13. Slice Stacking Traces out a luminous volume Objects are transparent Objects further in depth cannot be obscured

14. Slice Stacking Ideal for volumetric data sets and modeling problems Poorly suited to “photographic” or realistic images with hidden surfaces

15. Slice Stacking: Resolution and FOV Spatial resolution and FOV the same as underlying 2D display Varifocal mirrors limited to approximately 20 inches due to acoustic and mirror characteristics

16. Slice Stacking: Depth Resolution Depth of reflected CRT is constantly changing Very fine resolution of depth spots can potentially be imaged Limited by bandwidth of CRT and persistence of phosphors

17. Slice Stacking: Accommodation One of the few displays that support ocular accommodation Actually displays points in 3D space either directly or optically

18. Slice Stacking: Refresh Rate Refresh rate is twice frequency of vibration Typically 30 Hz signal drives mirror Results in 60 Hz refresh rate

19. Slice Stacking: Brightness Short persistence phosphors must be used Prevents smearing of image in depth Brightness somewhat reduced from “typical” 2D display Phosphors of short enough duration only available in green (circa 1986)

20. Slice Stacking: Viewing Zone Viewing zone limited by position of display CRT Obstructs viewing zone Can use beam splitter to move CRT below, but lowers brightness by at least 75%

21. Slice Stacking: Viewing Volume Magnification of mirror changes size of reflected CRT Results in truncated pyramid volume instead of rectangle

22. Slice Stacking: Volume Extent Mirrors have leverage of approximately 85 Distance h in mirror Movement 85h in reflected image

23. Slice Stacking: Number of Views Number of views essentially unlimited Horizontal and vertical parallax are both supported

24. Holography: CG Stereograms Recorded optically from a set of 2D views of a 3D scene Projects each 2D image into a viewing zone Stereo views with horizontal parallax Full-color, high resolution images Non-real time Requires a huge amount of information (100-300 views)

25. Holography: CG diffraction patterns Generates a diffraction pattern Hologram creates a 3D wavefront when illuminated Images 3D objects and light sources in space Traditional methods were complex and computationally expensive New method (circa 1992) allows generation to be displayed in real-time

26. Holography: Spatial Resolution Very high horizontal resolution is needed Vertical resolution can be lower High horizontal resolution is not resolution of displayed holographic image –Horizontal resolution of image points is diffraction limited –Beyond human perceptual limits

27. Holography: Miscellaneous Like slice-stacking displays, holograms support ocular accommodation Good brightness and contrast using low- power laser (a few milliwatts) Both monochromatic and color have been demonstrated Very high bandwidth compared to other systems

28. Holography: Miscellaneous Depth resolution is beyond human perceptual capabilities Provides many views from side-to-side No vertical parallax Viewing zone angle is determined by the frequency of diffraction pattern MIT system’s depth range limited to approximately 100mm MIT system’s refresh rate is 36 Hz with a little flicker

32. Any Questions?