11

Head-Mounted DisplayHead-Mounted DisplaySherman & Craig, pp. 151-159Sherman & Craig, pp. 151-159

22

Visually Coupled Systems Visually Coupled Systems

A system that integrates the natural visual and A system that integrates the natural visual and motor skills of an operator into the system he is motor skills of an operator into the system he is controllingcontrolling..

Basic ComponentsBasic Components

An immersive visual display (HMD, large screen An immersive visual display (HMD, large screen projection (CAVE), dome projection)projection (CAVE), dome projection)

A means of tracking head and/or eye motionA means of tracking head and/or eye motion

A source of visual information that is dependent A source of visual information that is dependent on the user's head/eye motion.on the user's head/eye motion.

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Head-Mounted DisplaysHead-Mounted Displays

Optical SystemOptical SystemImage Source (CRT or Flat Panel (LCD))Image Source (CRT or Flat Panel (LCD))See–Through or Non–See–ThroughSee–Through or Non–See–ThroughMounting ApparatusMounting Apparatus What are some factors?What are some factors?

EyeglassesEyeglassesWeightWeight

Solutions?Solutions?

EarphonesEarphonesPosition TrackerPosition Tracker

44

Field of ViewField of ViewMonocular 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.

55

Focal Length & DiopterFocal Length & Diopter

Focal LengthFocal Length - The distance from the - The distance from the surface of a lens (or mirror) at which rays surface of a lens (or mirror) at which rays of light converge.of light converge.

Diopter Diopter - The power of a lens is measured - The power of a lens is measured in diopters, where the number of diopters in diopters, where the number of diopters is equal to 1/(focal length of the lens is equal to 1/(focal length of the lens measured in meters).measured in meters).

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OcularityOcularity

OcularityOcularity

MonocularMonocular - HMD - HMD image goes to only image goes to only one eye.one eye.

Biocular Biocular - Same HMD - Same HMD image to both eyes.image to both eyes.

Binocular Binocular (stereoscopic) (stereoscopic) - - Different but matched Different but matched images to each eye.images to each eye.

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IPDIPD

Interpupillary Distance Interpupillary Distance (IPD)(IPD)

IPD is the horizontal IPD is the horizontal distance between a distance between a user's eyes.user's eyes.

IPD is the distance IPD is the distance between the two between the two optical axes in a optical axes in a binocular view binocular view system.system.

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Vignetting and Eye ReliefVignetting and Eye Relief

VignettingVignetting

The blocking or The blocking or redirecting of light rays as redirecting of light rays as they pass through the they pass through the optical system.optical system.

Eye Relief DistanceEye Relief Distance

Distance from the last Distance from the last optical surface in the optical surface in the HMD optical system to HMD optical system to the front surface of the the front surface of the eye.eye.

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Basic Eye Basic Eye

Cornea

CrystallineLens

Fovea

RetinaOpticNerve

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The EyeThe EyeAccommodationAccommodation - Term used to describe the altering of the - Term used to describe the altering of the curvature of the crystalline lens by means of the ciliary curvature of the crystalline lens by means of the ciliary muscles. Expressed in diopters.muscles. Expressed in diopters.

Retina Retina - The sensory membrane that lines the back of the - The sensory membrane that lines the back of the eye and receives the image formed by the lens of the eye.eye and receives the image formed by the lens of the eye.

Fovea Fovea - The part of the human retina that possesses the - The part of the human retina that possesses the best spatial resolution or visual acuity.best spatial resolution or visual acuity.

CorneaCrystallineLens

Fovea

RetinaOpticNerve

1111

Properties of the EyeProperties of the Eye

Approximate Field of ViewApproximate Field of View 120 degrees vertical120 degrees vertical 150 degrees horizontal (one eye)150 degrees horizontal (one eye) 200 degrees horizontal (both eyes)200 degrees horizontal (both eyes)

AcuityAcuity 30 cycles per degree (20/20 Snellen acuity).30 cycles per degree (20/20 Snellen acuity).

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Simple FormulasSimple Formulas

Visual Resolution in Cycles per degree Visual Resolution in Cycles per degree (V(Vresres) = Number of pixels /2(FoV in ) = Number of pixels /2(FoV in

degrees)degrees)

Example:Example: (1024 pixels per line)/(2*40 (1024 pixels per line)/(2*40 degrees) = Horizontal resolution of 12.8 degrees) = Horizontal resolution of 12.8 cycles per degreecycles per degree

To convert to Snellen acuity (as in 20/xx)To convert to Snellen acuity (as in 20/xx)

VVresres = 600/xx (20/47) = 600/xx (20/47)

1313

Optical SystemOptical System

Move image to a distance that can be Move image to a distance that can be easily accommodated by the eye.easily accommodated by the eye.

Magnify the imageMagnify the image

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Simple Magnifier HMD DesignSimple Magnifier HMD Design

p

q

Eyepiece(one or more

lenses)Display

(Image Source)

Eye f Image

1/p + 1/q = 1/f where1/p + 1/q = 1/f wherep = object distance (distance from image source to eyepiece)p = object distance (distance from image source to eyepiece)q = image distance (distance of image from the lens)q = image distance (distance of image from the lens)f = focal length of the lensf = focal length of the lens

1515

Thin Lens EquationThin Lens Equation

1/p + 1/q = 1/f where1/p + 1/q = 1/f where

p = object distance (distance from image source to eyepiece)p = object distance (distance from image source to eyepiece)

q = image distance (distance of image from the lens)q = image distance (distance of image from the lens)

f = focal length of the lensf = focal length of the lens

Conventions:Conventions:

If the incident light comes from the object, we say it is a real object, 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 and define the distance from the lens to it as positive. Otherwise, it is virtual and the distance is negative.is virtual and the distance is negative.

If the emergent light goes toward the image, we say it is a real 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.image, and define the distance from the lens to it as positive.

f = positive for a converging lensf = positive for a converging lens

A light ray through the center of the lens is undeflected.A light ray through the center of the lens is undeflected.

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Virtual Image Virtual Image

Lens Display

VirtualImage

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ResolutionResolution

(low) 160 x 120 color pixels per eye(low) 160 x 120 color pixels per eye

(high) 1000+ x 1000+(high) 1000+ x 1000+

Note that resolution and FOV are Note that resolution and FOV are independentindependent

Another important factor: pixel densityAnother important factor: pixel density Pixels per degree of FOVPixels per degree of FOV

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LEEP OpticsLEEP Optics

Large Expanse Extra Large Expanse Extra PerspectivePerspective

Give very wide field of Give very wide field of view for stereoscopic view for stereoscopic imagesimages

Higher resolution (more Higher resolution (more pixels) in the middle of pixels) in the middle of the field of view, lower the field of view, lower resolution on the resolution on the peripheryperiphery

Pincushion distortionPincushion distortion

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Fresnel LensFresnel Lens

A lens that has a surface A lens that has a surface consisting of a concentric consisting of a concentric series of simple lens sections series of simple lens sections so that a thin lens with a so that a thin lens with a short focal length and large short focal length and large diameter is possiblediameter is possible

More even resolution More even resolution distributiondistribution

Less distortionLess distortion

from lanternroom.comfrom lanternroom.com

2020

Relationship between angle and Relationship between angle and screen distance screen distance

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

Angle in Radians

Dis

tan

ce i

n m

m

Leep

Fresnel

2121

Distortion in LEEP OpticsDistortion in LEEP Optics

A rectangle Maps to this

How would you correct this?

2222

To correct for distortionTo correct for distortion

Must predistort imageMust predistort image

This is a pixel-based This is a pixel-based distortiondistortion

Graphics rendering uses Graphics rendering uses linear interpolation!linear interpolation!

Too slow on most systemsToo slow on most systems

Pixel shaders!Pixel shaders!

Render to TextureRender to Texture

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Distorted Field of ViewDistorted Field of View

Your computational model (computer Your computational model (computer graphics) assumes some field of view.graphics) assumes some field of view.

Scan converter may over or underscan, Scan converter may over or underscan, not all of your graphics image may appear not all of your graphics image may appear on the screen.on the screen.

Are the display screens aligned Are the display screens aligned perpendicular to your optical axis?perpendicular to your optical axis?

2424

Distance alongz-axis

Distorted FoV Distorted FoV (cont.)(cont.)

2525

Collimated: p=fCollimated: p=f

1/p + 1/q = 1/f q = 1/p + 1/q = 1/f q = , if p=f, if p=f

If the image source is placed at the focal If the image source is placed at the focal point of the lens, then the virtual image point of the lens, then the virtual image appears at optical infinity.appears at optical infinity.

f

2626

Compound Microscope HMD Compound Microscope HMD DesignDesign

Relay lens produces a real image of the display image Relay lens produces a real image of the display image source (screen) at some intermediate location in the source (screen) at some intermediate location in the optical train. The eyepiece is then used to produce an optical train. The eyepiece is then used to produce an observable virtual image of this intermediate image.observable virtual image of this intermediate image.

Relay Lens

ImageIntermediateReal Image

Eyepiece

ExitPupil

2727

Exit PupilExit Pupil

The area in back of the optics from which the The area in back of the optics from which the entire image can be seen. Important if IPD not entire image can be seen. Important if IPD not adjustable.adjustable.Compound microscope optical systems have a Compound microscope optical systems have a real exit pupil.real exit pupil.Simple magnifier optical systems do not have an Simple magnifier optical systems do not have an exit pupil.exit pupil.

Relay Lens

ImageIntermediateReal Image

Eyepiece

ExitPupil

2828

Virtual Research V8 HMDVirtual Research V8 HMD

DisplayDisplay Dual 1.3” diagonal Active Matrix Liquid Crystal Dual 1.3” diagonal Active Matrix Liquid Crystal

Displays Displays Resolution per eye: 640 x 480 (307,200 color Resolution per eye: 640 x 480 (307,200 color

elements)elements) focal length = 1mfocal length = 1m

OpticalOptical Field of view: 60° diagonalField of view: 60° diagonal

SolveSolve What is the cycles per degree?What is the cycles per degree? What is its horizontal and vertical field of view?What is its horizontal and vertical field of view?

Pros/ConsPros/Cons

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Characteristics of HMDsCharacteristics of HMDs

ImmersiveImmersive You are inside the computer worldYou are inside the computer world Can interact with real world (mouse, Can interact with real world (mouse,

keyboard, people)keyboard, people) Mask out real worldMask out real world

ErgonomicsErgonomics Length of use is limited, cue conflict!!! Length of use is limited, cue conflict!!!

(accomodation vs. parallax, perspective, etc.)(accomodation vs. parallax, perspective, etc.)

Resolution and field of viewResolution and field of viewTetheredTethered

3030

Exercise (Part of Quiz grade)Exercise (Part of Quiz grade)Due: October 20Due: October 20thth (Thursday) (Thursday)

Fill in the following table through research on the Internet:Fill in the following table through research on the Internet:

Virtual Virtual ResearchResearch

V8V8

ForteForte

VFXVFX

5DT5DT

HMD 800HMD 800

SonySony

GlasstronGlasstron

PLM-A35PLM-A35

1 column 1 column for best unit for best unit found for found for each each categorycategory

Resolution (RGB pixels)Resolution (RGB pixels)

FOV (d, w, h)FOV (d, w, h)

Distance from eye to Distance from eye to Virtual ImageVirtual Image

Stereo?Stereo?

PricePrice

WeightWeight

ProsPros

ConsCons