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3D and VR Displays

Lecture on SGN-5406 Virtual Reality course, Tampere University of Technology
by

Atanas Boev

on 19 March 2011

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Transcript of 3D and VR Displays

3D & VR Displays Exotic SGN-5406 Tampere University of Technology.
Department of Signal Processing Atanas Boev, firstname.lastname@tut.fi
partially based on lecture matherial by Ismo Rakkolainen What is the purpose of a display? To visualise natural or synthetic scene As faitfully
as possible Colour, HiDef, 3D Technologies Light Incandescence
(light bulb) Cathodoluminscence Photoluminscece (Cathode-ray tube + phosphor) (Phosphorercence)
Chemiluminiscence Bioluminiscence Auroras Worlds largest display! (light stick) Image CRT OLED AM (active-matrix)
OLED "Old" OLED, Short lifespan E-paper (Electroproretic) no backlight reflective
low power (page change) obligatory Kindle 3 photo :) LCD obligatory iPhone 4 photo :) RGB subpixels iPad iPhone iPhone 3GS iPhone 4 XO-1
(pixel Qi) Traditional LCD Colour sub-pixels Sub-pixel resolution voltage controlled polarization determined brigness of a pixel
even if fully on, much brigthness is lost
PDP
(plasma display) LED TMOS Many more... Temporary interleaved LED display Giant LED display LED backlight Fremont Street Experience
460m x 27m Pico projectors Micromirrors Reflected light Temporary interleaved colour EL, fast Pros/cons CRT
+speed
+colour gamut
-size
-weigth
-life LCD
+power
+size
+weigth
+cost
-speed
-brighntess Plasma
+brighntess
+speed
-power
-weigth
-size
-cost
-blue colour OLED
+brighntess
+speed
+power
+weigth
+flexible
-life e-ink
+power
+daylight operation
-resolution
-speed
-hard to backlight Retina scanning
+spees
+distortion free
+no crosstalk (3D)
-price
-size "Everything else :)" 3D printers Tactile displays Flyfire Static images... at the moment "Inbisibility cloak" Sixth sense @ MIT Water display Particle based Fog screen @ TUT Even more! Common technology Less common technology Image Properties To visualise abstract data Image Video Visualization Overlay Multichannel Logistics Colour Contrast Brightness Resolution Focal distance Field of View Head Parallax Field of Regard -Trichromatic (RGB)
spatially interleaved (sub-pixels) various interleave shapes
temporary interleaved -Four colour displays (Sharp aquios) -Monochrome displays Spatial resolution
PPI for digital displays
freq troughput for analog displays PPI of some digital displays is hard to estimate
exotic sub-pixel topologies
multiview displays iPhone "retina" displays is 326 DPI (42CPD at 30cm)
Human 20/20 vision is 50 CPD
Hold the iPhone at 45cm to achieve 50 CPD
(very few people have 20/20 vision anyway) Pixel latency in ms High latency introduces motion blur (temporal crosstalk) 25 FPS used in cinema 150 FPS used in 3D cinema
triple flash alternate
150/6=25 Can be pre-compensated Semi-transparent display See-trough data display
(Heads-up display, HUD) See-trough VR display
(head mounted) Semi-opaque display Augmented reality display
(mask real objects and replace with virtual ones) Possibility to remove annoying ads :) FoV in humans
200 degrees in horizontal direction
130 degrees in vertical direction
120 degrees binocular overlap
Immersive displays (CAVE)
can cover 100%
Cover of 100-120 degrees is reasonable
HMDs cover very limited FoV Field of view + head parallax CAVE with 6 walls surrounding user provides 100% FoR Ability to display scene from different angles
(as if to look behind monitor edges) Multiview display provide limited head parallax Head parallax can be achieved with head tracking Human vision links convergence with accomodation
–The focusing point of the eye (accommodation)
–Focal distance to the projection plane (display)
Confusing depth perception cues can cause objects to have an odd appearance Accomodation-convergence rivalry is one of the reasons causing ”simulator sickness” Other logistical actors related to displays used in various applications
Size (and floor space), weight (especially for head-mounted)
Interfaces
Hygiene and safety (e.g., for public HMDs)
Reliability
Indoor / outdoor, ergonomics, duration of use Some displays visualise multiple images simultaneously
3D displays
Multi-user displays When image intended for one chanel is visible in another ghoist images are introduced Laser projection DLP DLP chip by TI Types Non-immersive Immersive "Scene around user" "User around scene" Conclusion Example exam questions Presentation
software
prezi.com
lite version free for academic use Lab visit Questions? 2D 3D 3D Cave 3D HMD Added stereoscopy 3D Cinema 3D TV Objects are perceived at various depths
In front of the screen (negative disparity)
Behind the display (positive disparity) Principles of 3D perception Pictorial depth cues Head parallax Stereoscopy What is disparity? What do we need to see 3D image?
(more details in the next lecture) Two eyes are not absolutely necessary for 3D perception
Image depth cues, such as shados and perspective help see in 3D
5% of moviegoers are stereoscopically latent Each eye sees slightly different image of the scene Note: Focal depth must be consistent as well Ability to see different scene by looking from different place
Common approach is to use head-tracking
System detects head movement and renders image from new perspective Distance between observations in pixels Object appears in both channels
Object with depth appears on different places in each channel
Each observation has some absolute postion within the frame
Distance between observations in pixels is disparity
Negative disparity is perceived in front of display
Positive disparity is perceived behind display Autostereoscopic
displays Multiview Technologies Casts several images simultaneously
From a number of observation points, each eye sees different image Viewing diamonds
Optimal observation distance (more details in the next lecture) Cave Monitor Large screen HMD Holography Volumetric display Image is created inside
a volume, in 3D Swept volume Image is formed on
rotating surface Series of images are projected
syncronously with the rotation Each image represents 3D object
from particular angle Static volume Image is formed in transparent medium i.e. plasma balls in the air 4K cinema, multiple fused projectors
Hi-res projector, multiple resolutions fused Principles of operation Optics HMD models See-trough HMDs Head based VR Virtual retina display Uses two small displays embedded in a helmet
Using head tracking improves immersion
User can look around by moving its head
"The" VR display Lenses are used to give the perception that the images are coming from a great er distance Optical see-trough
Simpler (cheaper)
Direct view of real world
Full resolution, no time delay (for real world)
Safety while moving
Lower distortion
No eye displacement Videomix see-trough
True occlusion
Digitized image of the real world
Flexibility in composition
Matchable time delays
More registration, calibration strategies
Wide FOV is easier to support Also known as "Binocular Omni-Orientation Monitor" (BOOM)
The display is attached to electromechanically tracked booms. Cinemizer Plus (Carl Zeiss) Stereo, 2x VGA
Works with iPod
Works with analogue PAL video
Sub 400 euro 5DT HMD 800-26 3D Stereo, 2x SVGA
3000 euro I-O Displays i-glasses i3PC Stereo, 2x SVGA
Works with PC
~700 euro Cybermind Visette45 SXGA Stereo, 2x 1280x1024
Price: ask :) Many other models available... An image is formed directly on the retina of the user's eye
Draws a raster display directly onto the retina of the eye
Calligraphic and raster scan patterns are possible
Like a CRT in television
With VRD, no real image is ever produced! also, multiple-monitor displays Fish-tank VR (scene appears bounded by the monitor frame, like in a fish-tank) Might employ stereoscopic glasses and head tracking General principle Designs IMAX Flight Simu CAVE painting C.A.V.E. - Cave Automatic Virtual Environment (recursive acronym) Immersive image is seamlessly projected on surrounding surfaces Usually very expensive
open source software libraries exist
graphical cards are getting more powerfull Ball-shaped CAVEs "Personal" CAVE (i-cocoon) Immersive displays VisionStation, 20 - 165,000 €
VisionDome, 150 – 270,000 € Panoscope Extra large film size IMAX dome IMAX theatre IMAX 3D Immersive display
CAVE
3D orientation
Force feedback 3D interaction in virtual space using virtual "tools" Cave painting in the past... Not ready yet. Expected in Q1 2020 :) / Temporal multiplex
(Shutter glasses) Polarization multiplex Colour multiplex
(Anaglyph) Wavelength multiplex Operation:
Cannels encoded with (nearly) complenetar colours
Each eye sees the SHAPE of the corresponding channel
Each eye sees differently coloured image
It is believed that brain reconstructs full colour range
Various colour pairs can used Advantages:
Cheap
Can be used for colour 3D images Disadvantages:
Colour range is limited
Colour imbalance (problems after long use, post-effects)Anaglyph glasses are main reason for industry "black eye" of 3D in 60s Colour perception:
Human eye is sensitive to three "narrow" frequency bands
Eye can reconstruct full colour from three sharp frequency peaks (that's how RGB display works!)
The _exact_ position of the peak is not important Operation:
Each channel is transmitted trough colour filter passing three narrow frequencies
Position of peaks in each channel is slightly different
Highly selective filter is placed infront of each eye Disadvantages:
Expensive
Brightness loss Cinema use (XpanD) PC/Laptop use (NVidia) Operation:
Images for left and right eye are shown temporary interleaved with (at least) double framerate
Shutter-glasses are suncronized with the framerate (IR, cable, polarized watermark)
When "left" image is displayed, shutter glasses "cover" the right eye, and vice versa Properties
+ low(er) crosstalk
+needs only one (hi speed) projector/display
-expensive glasses
-fast refresh rate is needed (>>50FPS) to avoid eye-strain RealD cinema glasses Operation:
Two projectors are user (more expensive)
Each channel is polarized differently
Both channels are projected on the same (polarization preserving!) surface
Each eye sees the intended channel
Crosstalk might be ~ 20-30% even 50% Linear polarization
i.e. horizontal and vertical
user mush keep head straigth Curcular polarization
i.e. clockwise and counter-clockwise
user can tilt head (but stereo is bad!) Types of 3D glasses Adding stereoscopic 3D Binocular Principles of
operation Display casts multiple
images (some sub-pixels seen from some angles only) Images are directionally
multiplxed (different image for different observation angle) Each eye sees different image Each image shows the same scene from different angles Stereoscopic 3D effect! Leticular sheet
Similar to 3D postcards
Usually slanted
Unidirectional head parallax (images change in horizontal direction only Parallax barrier
Most common
Cheaper to produce
Blocks most of the light - diminished brightness Spherical sheet
Multidirectional head parallax
Resolution suffers
Hard to produce, hard to mount, hard to generate content Half of sub-pixels visible by one eye
(other half by other eye) 2D/3D switchable barrier Quasiholographic Pros/cons Holovisio by Holografika
uses number of back-projectors
not fully holographic (replicated ray directions but not phase)
Each pixel (voxel) can emit light with different colour in different direction Minuses
Multiview displays require multichannel video
Limited "sweet spot"
Crosstalk! Pluses
Easy to produce (reuses TFT displays)
No glasses
Suitable for mobile applications Affected by ambient light Affected by distance (projectors) High dynamic range displays
(range 40000:1) See-trough displays need high brightness Difference between levels of black and white Contrast linearity Level of black
high black levels in projectors (gray!)
depends on display reflectance
extra low black level displays (Pioneer KURO) f
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