Transcript Head-Mounted Display

Head-Mounted Display
Sherman & Craig, pp. 151-159
1
Visually Coupled Systems
A system that integrates the natural visual and
motor skills of an operator into the system he is
controlling.
Basic Components
An immersive visual display (HMD, large screen
projection (CAVE), dome projection)
A means of tracking head and/or eye motion
A source of visual information that is dependent
on the user's head/eye motion.
2
Head-Mounted Displays
Optical System
Image Source (CRT or Flat Panel (LCD))
See–Through or Non–See–Through
Mounting Apparatus

What are some factors?
Eyeglasses
Weight

Solutions?
Earphones
Position Tracker
3
Field of View
Monocular FOV is the angular subtense
(usually expressed in degrees) of the
displayed image as measured from the
pupil of one eye.
Total FOV is the total angular size of the displayed image
visible to both eyes.
Binocular(or stereoscopic) FOV refers to
the part of the displayed image visible to
both eyes.
FOV may be measured horizontally,
vertically or diagonally.
4
Focal Length & Diopter
Focal Length - The distance from the
surface of a lens (or mirror) at which rays
of light converge.
Diopter - The power of a lens is measured
in diopters, where the number of diopters
is equal to 1/(focal length of the lens
measured in meters).
5
Ocularity
Ocularity
Monocular - HMD
image goes to only
one eye.
Biocular - Same
HMD image to both
eyes.
Binocular
(stereoscopic) Different but matched
images to each eye.
6
IPD
Interpupillary Distance
(IPD)
IPD is the horizontal
distance between a
user's eyes.
IPD is the distance
between the two
optical axes in a
binocular view
system.
7
Vignetting and Eye Relief
Vignetting
The blocking or
redirecting of light rays as
they pass through the
optical system.
Eye Relief Distance
Distance from the last
optical surface in the
HMD optical system to
the front surface of the
eye.
8
Basic Eye
Cornea
Crystalline
Lens
Fovea
Retina
Optic
Nerve
9
The Eye
Accommodation - Term used to describe the altering of the
curvature of the crystalline lens by means of the ciliary
muscles. Expressed in diopters.
Retina - The sensory membrane that lines the back of the
eye and receives the image formed by the lens of the eye.
Fovea - The part of the human retina that possesses the
best spatial resolution or visual acuity.
Cornea
Crystalline
Lens
Fovea
Retina
Optic
Nerve
10
Properties of the Eye
Approximate Field of View



120 degrees vertical
150 degrees horizontal (one eye)
200 degrees horizontal (both eyes)
Acuity

30 cycles per degree (20/20 Snellen acuity).
11
Simple Formulas
Visual Resolution in Cycles per degree
(Vres) = Number of pixels /2(FoV in
degrees)
Example: (1024 pixels per line)/(2*40
degrees) = Horizontal resolution of 12.8
cycles per degree
To convert to Snellen acuity (as in 20/xx)
Vres = 600/xx (20/47)
12
Optical System
Move image to a distance that can be
easily accommodated by the eye.
Magnify the image
13
Simple Magnifier HMD Design
q
p
f
Eye
Eyepiece
(one or more lenses)
Image
Display
(Image Source)
1/p + 1/q = 1/f where
p = object distance (distance from image source to eyepiece)
q = image distance (distance of image from the lens)
f = focal length of the lens
14
Thin Lens Equation
1/p + 1/q = 1/f where
p = object distance (distance from image source to eyepiece)
q = image distance (distance of image from the lens)
f = focal length of the lens
Conventions:
If the incident light comes from the object, we say it is a real object,
and define the distance from the lens to it as positive. Otherwise, it
is virtual and the distance is negative.
If the emergent light goes toward the image, we say it is a real
image, and define the distance from the lens to it as positive.
f = positive for a converging lens
A light ray through the center of the lens is undeflected.
15
Virtual Image
Virtual
Image
Lens
Display
16
Resolution
(low) 160 x 120 color pixels per eye
(high) 1000+ x 1000+
Note that resolution and FOV are
independent
Another important factor: pixel density

Pixels per degree of FOV
17
LEEP Optics
Large Expanse Extra
Perspective
Give very wide field of
view for stereoscopic
images
Higher resolution
(more pixels) in the
middle of the field of
view, lower resolution
on the periphery
Pincushion distortion
18
Fresnel Lens
A lens that has a surface
consisting of a concentric
series of simple lens sections
so that a thin lens with a
short focal length and large
diameter is possible
More even resolution
distribution
Less distortion
from lanternroom.com
19
Relationship between angle and
screen distance
80.00
60.00
50.00
Leep
40.00
Fresnel
30.00
20.00
10.00
2.
00
6.
00
10
.0
0
14
.0
0
18
.0
0
22
.0
0
26
.0
0
30
.0
0
34
.0
0
0.00
R
Distance in mm
70.00
Angle in Radians
20
Distortion in LEEP Optics
A rectangle
Maps to this
How would you correct this?
21
To correct for distortion
Must predistort image
This is a pixel-based
distortion
Graphics rendering
uses linear
interpolation!
Too slow on most
systems
Pixel shaders!
Render to Texture
22
Distorted Field of View
Your computational model (computer
graphics) assumes some field of view.
Scan converter may over or underscan,
not all of your graphics image may appear
on the screen.
Are the display screens aligned
perpendicular to your optical axis?
23
Distorted FoV (cont.)
Distance along
z-axis
24
Collimated: p=f
1/p + 1/q = 1/f
q = , if p=f
If the image source is placed at the focal
point of the lens, then the virtual image
appears at optical infinity.
f
25
Compound Microscope HMD
Design
Relay lens produces a real image of the display image
source (screen) at some intermediate location in the
optical train. The eyepiece is then used to produce an
observable virtual image of this intermediate image.
Exit
Pupil
Intermediate
Real Image
Eyepiece
Image
Relay Lens
26
Exit Pupil
The area in back of the optics from which the
entire image can be seen. Important if IPD not
adjustable.
Compound microscope optical systems have a
real exit pupil.
Simple magnifier optical systems do not have an
exit pupil.
Exit
Pupil
Intermediate
Real Image
Eyepiece
Image
Relay Lens
27
Virtual Research V8 HMD
Display



Dual 1.3” diagonal Active Matrix Liquid Crystal
Displays
Resolution per eye: 640 x 480 (307,200 color
elements)
focal length = 1m
Optical

Field of view: 60° diagonal
Solve


What is the cycles per degree?
What is its horizontal and vertical field of view?
Pros/Cons
28
Characteristics of HMDs
Immersive



You are inside the computer world
Can interact with real world (mouse,
keyboard, people)
Mask out real world
Ergonomics

Length of use is limited, cue conflict!!!
(accomodation vs. parallax, perspective, etc.)
Resolution and field of view
Tethered
29
Exercise (Part of Quiz grade)
Due: October 20th (Thursday)
Fill in the following table through research on the Internet:
Virtual
Research
V8
Forte
VFX
5DT
HMD 800
Sony
Glasstron
PLM-A35
1 column
for best unit
found for
each
category
Resolution (RGB pixels)
FOV (d, w, h)
Distance from eye to
Virtual Image
Stereo?
Price
Weight
Pros
Cons
30