Three Dimensional Visual Display Systems for Virtual Environments

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 approximatelywhere λ is the wavelength of light passing through the slit θ= 2 asin ( λ / α ) α = pitchslit / 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 B0 is brightness of unblocked screen Brightness = B0 * ( α / pitchslit )

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?