Head-Mounted Display Sherman & Craig, pp. 151-159

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. Larry F. Hodges

Head-Mounted Displays Optical System Image Source (CRT or Flat Panel (LCD)) See–Through or Non–See–Through Mounting Apparatus Earphones Position Tracker Larry F. Hodges

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. Larry F. Hodges

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). Larry F. Hodges

Ocularity and IPD Ocularity Interpupillary Distance (IPD) Monocular - HMD image goes to only one eye. Biocular - Same HMD image to both eyes. Binocular (stereoscopic) - Different but matched images to each eye. 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. Larry F. Hodges

Vignetting and Eye Relief 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. Larry F. Hodges

Optical System Move image to a distance that can be easily accommodated by the eye. Magnify the image Larry F. Hodges

Simple Magnifier HMD Design o f Image Eye Eyepiece (one or more lenses) Display (Image Source) Larry F. Hodges

Virtual Image f f Virtual Image Display Lens Larry F. Hodges History: Wartell: Redrew diagram correctly – I could make no sense of original diagram. Display Lens Larry F. Hodges

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 Larry F. Hodges

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 Larry F. Hodges

Relationship between angle and screen distance Larry F. Hodges

Distortion in LEEP Optics A rectangle Maps to this Larry F. Hodges

To correct for distortion Must predistort image This is a pixel-based distortion Graphics rendering uses linear interpolation! Too slow on most systems Larry F. Hodges

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? Larry F. Hodges

Distorted FoV (cont.) Distance along z-axis Larry F. Hodges

Collimated: o=f 1/o + 1/i = 1/f i = , if o=f If the image source is placed at the focal point of the lens, then the virtual image appears at optical infinity. f Larry F. Hodges

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. Relay Lens Image Intermediate Real Image Eyepiece Exit Pupil Larry F. Hodges

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

Virtual Research V6 HMD Display Optical Dual 1.3 diagonal Active Matrix Liquid Crystal Displays Resolution per eye: 640 x 480 (307,200 color elements) Optical Field of view: 60° diagonal Larry F. Hodges

What is the horizontal resolution in cycles per degree? Horizontal FoV? Equivalent to how many RGB pixels of horizontal resolution? (Horizontal Resolution) / 2*Horizontal FoV 3.85 Cycles per degree or 20/156 Larry F. Hodges

Characteristics of HMDs Immersive You are inside the computer world Can interact with real world (mouse, keyboard, people) Ergonomics Resolution and field of view Tethered Larry F. Hodges