Virtuelle Realität. Overview. Teil 5: Visual Displays. Prof. Bernhard Jung. Virtuelle Realität

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1 Teil 5: Visual Displays Virtuelle Realität Wintersemester 2007/08 Prof. Bernhard Jung Overview Stereoscopy and other visual depth cues Properties of visual displays visual presentation qualities logistic qualities of visual displays Stationary visual displays fish tank VR projection-based Head-based VR Handheld VR See also: Sherman & Craik. Understanding Virtual Reality. Morgan Kaufmann Chapter 4. C. Ware. Information Visualization: Perception for Design. Second Edition. Morgan Kaufmann

2 Visual Depth Cues Standard (monoscopic) 3D rendering gives depth cues: occlusion (strongest depth cue) perspective relative size texture gradient (shadows) To enhance 3D depth, use stereo imagery Slightly different images for each eye Visual Depth Cues Monocular Depth Cues occlusion + height occlusion + height + perspective atmospheric/aerial perspective reduce contrast with distance shadows texture gradient cobblestone pattern as depth cue 2

3 Visual Depth Cues - Implementing stereoscopy Render from two offset eye points 2 images per frame may affect frame rate multiple graphics pipelines each image lower resolution HMD: directly send images to 2 eyes other displays: time-multiplexed stereo (shutter glasses) using phase filters using color filters autostereoscopic displays Visual Depth Cues - Stereoscopy Wheatstone stereoscope (1838) 3

4 Visual Depth Cues - Stereoscopy Shutter Technology Close left eye when right eye image is displayed and vice versa Controlled through infrared or wired up Visual Depth Cues - Stereoscopy Stereo Through Polarization Light: wave length and direction of polarization. Linear polarization Polarization filters 4

5 Visual Depth Cues - Stereoscopy Polarization Use two projectors Projector 1/left view: vertical filter in front of the lens Projector 2/right view: horizontal filter in front of the lens Wear glasses with polarization filters Left eye: vertical Right eye: horizontal Visual Depth Cues - Stereoscopy Polarization Linear polarization Can t tilt head Little ghosting Circular polarization Principle: counter clockwise / clockwise Allows arbitrary head orientations In general more ghosting than linear polarization 5

6 Visual Depth Cues - Monocular Depth Cues Motion Parallax Even more important depth cue than stereo: motion parallax far objects move more slowly across the visual field as our viewpoint moves Can achieve motion parallax with head tracking Tracking also allows us to view the scene naturally When viewed from Viewpoint A, the object appears to be closer to the blue square. When the viewpoint is changed to Viewpoint B, the object appears to have moved in front of the red square. source: wikipedia Visual Depth Cues Relative Importance Normalized measurable distance change Motion parallax 0.1 Binocular disparity Convergence accommodation 1.0 Height in field Aerial Depth (meters) Occlusion Relative size Cutting,

7 Properties of Visual Display Paradigms Visual presentation qualities resolution color contrast brightness number of display channels focal distance opacity masking field of view (FOV) field of regard (FOR) graphics latency tolerance frame rate Visual presentation qualities Resolution number of pixels pixel density Color tri-chromatic color in most monochromatic in some especially see-through head-based displays (HBDs), e.g. red laser field-sequential color maps all primary colors onto same dot clearer image when viewed from close ranges (conventional displays place combinations of colors in very close groups) 7

8 Visual presentation qualities Contrast/brightness dynamic range of the display LCD displays tend to have lower contrast than CRTs how bright are light sources? see-through AR displays require brighter displays Number of channels usually two for stereoscopic displays some VR systems offer four-channel displays support for two users e.g. FakeSpace DuoView sometimes monocular (single-eye) displays in Augmented Reality Visual presentation qualities lens curvature changes when focusing to far and near objects Focal distance distance at which images seem to appear with current display technology, all images are on the same focal plane typically the screen in stationary displays can be infinite via optics in an head-based display eye muscles adjust to focal distance "accommodation" a visual depth cue incongruity between focal distance (accommodation) and other visual depth cues (stereopsis, perspective, ) can lead to eye strain, or worse 8

9 Visual presentation qualities Opacity occlude the real world, or not CAVE does not occlude the real world most head-based displays do occlude the real world AR applications require displays that do allow the real world to be seen Masking body parts and objects held by user occlude, or mask, virtual objects in stationary displays similarly, virtual objects, when between the participant's eye and real objects should mask these real objects but this does not happen see-through head-based displays can accommodate this if the masking objects are tracked not a concern in occlusive head-based displays all visible objects rendered by the computer system Visual presentation qualities Field of view (FOV) measure of the angular width (and height) of a user's vision measured as a percentage, or as angles human vision is approximately 200 degrees total, with 120 degrees of overlap tunnel vision is considered to be a 60 degree FOV or less typical head-based displays cover about 100 degrees total FOV with about 60 degrees of overlap 9

10 Visual presentation qualities Field of Regard (FOR) amount surrounding space where virtual world is displayed measured as a percentage head-based displays are typically 100% stationary displays are often much less except for 6-sided CAVEs Visual presentation qualities Graphics latency tolerance how detrimental is lag to quality of the display? lag is very noticeable when rotating head in head-based display lag is less noticeable when rotating head in stationary display because a view of world from the new direction was already there (just a little old) Frame rate image updates per second (measured as FPS or Hz) motion pictures capture 24 FPS 15 Hz is considered marginally acceptable 10 Hz and below causes brain to notice that it is seeing a series of still images 10

11 Properties of Visual Display Paradigms Logistic qualities of visual displays user mobility interface with tracker methods environment requirements associability with other sense displays portability throughput encumbrance safety cost Logistic qualities of visual displays User mobility effect on (mental) immersiveness and usefulness e.g. cables that tether the user or screens that prevent further physical movement Environment requirements conditions of the surrounding space necessary to provide a good VR experience projected images require low light large stationary displays require big rooms head-based displays are best choice in tight quarters (e.g. a training task used on a submarine) 11

12 Logistic qualities of visual displays Associability with other sense displays headphones and head-based displays work well together speakers are good for stationary displays, except they mask the screen (or the sound is masked by the screen) Portability large stationary displays are not portable head-based displays can practically be run off a laptop (though not in stereo) Logistic qualities of visual displays Throughput many people can see the screen in a CAVE easier for people to enter/exit a CAVE, and to pass stereo glasses from one person to another Head-based displays often require a minute or two to change viewers Encumbrance generally more wires associated with head-based displays stereo shutter glasses operate wirelessly wireless tracking can be done Safety can't see what you're doing (in the real world) in an occlusive head-based display eye fatigue and nausea can result from poor optics in an HBD Cost large stationary screen displays are generally expensive CAVE like devices also require a large room The CAVE also requires more graphics power high resolution head-based displays not exactly cheap either 12

13 Visual Displays for Virtual Reality Visual display options stationary displays Fish Tank and Projection VR displays that move with the head (head-coupled) occlusive and non-occlusive displays that move with the hand (hand-coupled) palm VR Fish Tank VR Monitor-based systems Use e.g. shutter glasses autostereoscopic displays fewer components / lower cost standard interface devices available (keyboard, mouse, joystick) limited FOR limited FOV generally less mentally immersive 13

14 Fish Tank VR Autostereoscopic Displays Conventional TFT plus prism mask / beam splitter prism mask may be movable (in conjunction with camera-based head tracking) DTI Virtual Window SeeReal, Dresden Sharp Actius Projection-based VR Use video projectors Rear or front projection Active or passive stereo Commonly used 14

15 Projection Walls Active or passive stereo Multi-projector systems require overlap active passive Cylindrical Screen Configurations Common in industry Head tracking difficult Curved screen requires distortion correction in software 15

16 Workbench Table-top metaphor Change display orientation Integrate real & virtual Less immersion Immersion breaks at the display borders Responsive Workbench Responsive Workbench, GMD, 1993 Pictures from University of Bielefeld 16

17 More Workbench Designs IR Controllers CRT Projector Mirrors Tilting mechanism BARCO Baron workbench BARCO Virtual Surgery Table Two-Sided Workbench View volume Telepresence GMD/TAN 1997/98 Barco Consul 17

18 Wall Wall/door metaphor Allows 1:1 real object sizes High resolution Screen size limit Immersion breaks at the display borders Curved Screen Immersive Projection Environment BARCO 18

19 CAVE "In the CAVE, you are no longer on the outside looking in but on the inside looking out." Thomas DeFanti, co-developer of the CAVE Multi-wall (3-6) provides wide FOV Can see other people Stereo more realistic Missing walls break illusion (Less bright with CRT) space requirements CRT Projector Screen Mirror CAVE 3-D large volume display (courtesy of Fakespace Co.) 19

20 Head-based VR Small, lightweight screens Mental immersion relies mostly on head orientation 100% FOR Wide range of resolution (correlated with cost & weight) More portable than stationary displays Lag in tracking is more detrimental Generally lacking in FOV Generally more encumbering than stationary displays Lengthy use difficult due to increased eye strain One size fits all? 20

21 1968: Sutherland A head-mounted three-dimensional display Hidden-line graphics Mechanical tracking See-through HMD Head-mounted display Scene completely surrounds user Graphics are sharp and bright FOV is narrow Devices are heavy, cumbersome Can t see other people 21

22 BOOM (Binocular Omni Orientation Monitor) one of the oldest VR display types High resolution Wide Field of View User must not carry heavy weight Electromechanical tracking with minimal lag Limited user movement Requires the user to hold onto the BOOM for control See-through head-based displays Choice of optical vs. video method of "see-through" Tracking must be full 6-dof (location and orientation) Tracking must be well registered with the real world Applications must live within the restrictions of the real world Proper rendering of object occlusion is difficult studierstube.org SAABtech AddVisor

23 See-through head-based displays HBD Lifestyle? Vuzix, formerly Icuiti Video Eyewear 23

24 Handheld VR Limited examples of handheld VR/AR have been implemented "Magic Lens" augment physical objects with digital information Need to track both the screen and the head Tracking needs to be registered with the real world Other visual display types 24

25 Other visual display types Heliodisplay Benefits of stationary displays (Fishtank & Projection) higher resolution (than most HMDs) wider field-of-view longer user endurance (ie. can stay immersed for longer periods) higher tolerance for display latency more user mobility (less cables) less encumbering less safety risk better for group viewing Benefits of head-coupled displays (occlusive & non-occlusive) lower cost (for lower resolution models) complete field-of-regard better portability can be used for augmenting reality less physical space required (compared to multi-screened stationary displays) can occlude the real world (required in some situations) less concern for room lighting, etc. Benefits of hand-coupled displays better mobility better portability can be combined with stationary displays 25