Human Factors and Displays for VR Graphics David

Human Factors and Displays for VR Graphics David Johnson

Goals • Learn about – Human vision – Methods presenting images to users

Visual Bandwidth • Bandwidth of vision is probably greater than other sensory modalities – Retina bandwidth ~10 Mbits/sec • article – Most important sense for VR? • IMAX movie of rollercoaster can induce sensation of motion • Images can induce sensations of taste/smell

Why Study Basis of Vision? • If a display can match human capabilities, we are done • If the display can’t, nice to know where to concentrate resources. • Maybe can use tricks to suggest a higherquality display – Optical illusions

Anatomy of Vision

Eye Anatomy

Blind Spot test • Test – Brain fills in

Eye Optics

Accomodation • Change in curvature of lens – Rest focus from 6 m to infinity

Light Sensors • Cones – Mostly in the fovea – Blue, green, red/yellow cones, also called short, medium, long • Rods – Sense low levels of light

Visual Acuity • Cycles per degree – Like angular resolution – Humans can resolve 0. 93 mm spacing at 1 m – Fovea is about 1 Mpixel • 1 arc minute at fovea ( 1/60 degree) – 20/20 vision letters are 5 arc minute letters (strokes 1 arc minute) • Around 24 K x 24 K over field of view – Retina is sensitive to light levels over 10^13 range • Dynamic

Visual Field • One Eye – 120 degrees vertically and 150 degrees horizontally • 60 to nose, 90 to side • 50 up, 70 down • Binocular 200 degrees horizontal • Eye can rotate about 50 degrees

Binocular Vision • Humans have 120 degree binocular overlap – 2 40 degree monocular regions • Depth disparity perception – 0. 05 mm at 500 mm – 4 mm at 5 m

Eye Motion • Vergence - the motion of the eye to maintain binocular vision – ‘Cross-eyed’ when focus in close • Version – eye movement in the same direction • Duction – motion of one eye • Eye makes compensatory motions when head moving – Shake hand vs. shake head • Saccades – eye movement to use fovea more • Microsaccades – imperceptible motions to maintain excitation of rods and cones

Frame rate • 60 Hz frame rate is generally considered important – flicker fusion at ~60 Hz • Old movies at low rates but people weren’t sensitized to it

Visual Displays • How do we get computers to interact with the eye?

Overview • display technologies • • head-mounted displays (HMD) projection-based displays

Overview • Characteristics of displays • • field of view stereo display resolution issues brightness

HMD • • head-mounted displays (hmd) technology • • displays: LCDs, CRTs, OLEDs, other totally immersive display experience tend to have small FOV (as compared to a more natural FOV) often bulky

HMD • • two displays provide image for left and right eye see-through displays used for augmented reality • • semi-transparent overlays or video see-through What did Brooks say was an advantage of video merge vs optical merge?

HMD characteristics • what are important characteristics? • • • image resolution, brightness, contrast • tied to visual acuity field of view the mechanics • ergonomics, mass, moments of inertia

field of view - FOV • field of view - can mean different things • • • optical field of view - field of view as specified by the HMD optics rendered field of view - field of view as specified in software Mapping between the two of them

field of view - FOV • field of regard - the total area over which a user can view • • afford visual integration of larger space for HMDs this is generally 360 degrees • provided the head is tracked for projection systems, generally closer to 180 degrees CAVE varies

hmd display optics • optics between the image plane and the user’s eye produce a virtual image farther away from the eye • • reduces accommodative effort ideally out a few meters to help eye cancel out convergence/accommodative rivalry optics magnify pixel granularity! • other distortions? Leep optics – radial falloff – needs defocus distance screen optics virtua

HMD displays • • CRT-based HMDs • electron beam aimed at phosphorescent screen, resulting in emitted light generally good picture quality but often heavier and much more expensive Now rare

• example of CRT-based HMD Datavisor Hi. Res, Datavisor 80 Datavisor Hi. Res: 1280 x 1024, 1. 9’/pixel, 42° fov (100% overlap), about 4 lbs, uses monochrome CRT w/ color filter shutters Datavisor 80: 1280 x 1024, 3’/pixel, accommodation at infinity, 80° diagonal fov, 120° with 20% overlap, about 5 lbs

nvis n. Visor SX • • • liquid crystal on silicon (LCo. S) LCD-type device by CRLOpto 0. 9” microdisplay with 1280 x 1024 resolution horizontal fov: 47°, weight: 2 lbs good image quality, brightness, and contrast

LCD-based hmds • • • in general, LCD HMDs have been less expensive and lighter however, • • • usually, much lower resolution poorer image quality lower brightness, contrast improvements in LCD technology but VR just now catching up

LCD-based HMDs • Virtual Research V 8 • • 640 x 480 resolution approx 45° fov (100% overlap) lightweight: ~2 lbs inexpensive: ~$12 k

other HMDs • • Kaiser • • • resolution 1024 x 768 about $15 k uses active matrix LCD screens Kaiser Pro. View XL 50 2. 3’/pixel 40° fov just over 2 lbs OLED-based HMDs - better brightness than LCDs, 800 x 600 • • • good image quality, lighter $5 k, but with low fov (28°) may have short life span 5 DT HMD 800

Sensics • First new HMD in some time • Array of microdisplays • OLEDs • Panoramic field of view • 2. 9’/pixel

• • setting up stereo monocular: image viewed with one eye only bi-ocular: both eyes see the same image binocular: each eye sees its own image HMDs approximate stereo vision by showing a user left and right eye images • • what if the person can’t fuse stereo? What about vergence? what about IPD? • • IPD = inter-pupillary distance is this important? most HMDs do not provide enough control over the exact settings

perception and fov/stereo • • common explanations for problems in VR: • • • didn’t use stereo was configured improperly truth of the matter is that no one really knows in general for all situations • • • too small fov requires specific experimentation with • different setups, tasks, and applications FOV is likely important for speed of localizing stereo is likely very important for near field interaction

other pros/cons of HMDs • • • definite advantages: • fully immersive disadvantages: • • bulky, heavy, obtrusive poor resolution, mismatch between accommodation/convergence other comments?

projection displays • • setup a projector, aim it at a screen • you’re doing VR research! actually a little more complex than that goal is to surround user with the virtual environment good concept • • potentially reduces locomotion abilities capability to increase resolution dramatically • tiling the display projectors

cave • cave • • • CAVE Automatic Virtual Environment developed at U Illinois-Chicago 1992 did you know CAVE is trademarked?

stereo with projection vr • with HMDs, stereo vision is potentially easier (minus bad artifacts) • • two images, one for each eye for projection vr, you have two choices • • active stereo passive stereo

active stereo • • • shutter glasses are required left and right eye shutters on the glasses synchronize with images coming from projector crystal eyes • • transmitter synced up with graphics/projector system turns right and left shutters on/off

ia state cave

passive stereo • use the polarization of light to passively send stereo • • two projectors per screen, each with different polarizing filters left and right eyes of glasses allow the correct polarized light through potentially less expensive people just wearing “sun glasses”

important stereo issues • • generally, very expensive! • • requires extremely bright projection systems projectors must be capable of high refresh rates (120 Hz) for active stereo bright projectors are required due to issue with light efficiency • • • first off, about half of light is lost due to left/right switching glasses passive stereo - between 12% and 59% depending on setup Screen transmission

• other painful issues with projection vr alignment matters • • for stereo setups, especially passive stereo, alignment is crucial for tile-able displays with high resolution • images must overlap and blend

• other painful issues with projection vr actually, should be able to project on any surface • large set of research devoted to • • • automatic alignment image blending, color matching projection onto arbitrary surfaces • not just flat walls

Desktop VR • Also known as “fishtank” VR • Use computer monitor – Track head – Stereo from shutter glasses

vision dome and other spherics

Workbench

Autostereoscopic displays

Volumetric displays • Actuality – Rotating screen