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
• Test
– Brain fills in
Eye Optics
Accomodation
• Change in curvature of lens
– Rest focus from 6m 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 0.93mm spacing at 1m
– 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 24K x 24K 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
– 0.05mm at 500mm
– 4mm at 5m
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
• 60Hz frame rate is generally considered
important
– flicker fusion at ~60Hz
• 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
focus distance
screen
optics
virtua
HMD displays
•
CRT-based HMDs
•
electron beam aimed at phosphorescent
screen, resulting in emitted light
•
•
generally good picture quality
•
Now rare
but often heavier and much more
expensive
•
example of CRT-based HMD
Datavisor HiRes, Datavisor 80
Datavisor HiRes: 1280x1024, 1.9’/pixel, 42°
fov (100% overlap), about 4lbs, uses
monochrome CRT w/ color filter shutters
Datavisor 80: 1280x1024, 3’/pixel,
accommodation at infinity, 80°
diagonal fov, 120° with 20%
overlap, about 5lbs
nvis nVisor SX
•
•
•
•
•
liquid crystal on silicon (LCoS)
LCD-type device by CRLOpto
0.9” microdisplay with
1280x1024 resolution
horizontal fov: 47°, weight: 2lbs
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 V8
•
•
•
•
640x480 resolution
approx 45° fov (100% overlap)
lightweight: ~2lbs
inexpensive: ~$12k
other HMDs
•
•
Kaiser
•
•
•
•
•
•
resolution 1024x768
about $15k
uses active matrix LCD screens
Kaiser ProView XL50
2.3’/pixel
40° fov
just over 2lbs
OLED-based HMDs - better brightness
than LCDs, 800x600
•
•
•
good image quality, lighter
$5k, but with low fov (28°)
may have short life span
5DT 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
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
•
good concept
goal is to surround user with the virtual
environment
•
•
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 (120Hz) 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