Head-mounted display

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an HMD

A head-mounted display (HMD) is a display device that a person wears on the head to have video information directly displayed in front of the eyes.

[edit] Overview

An HMD has either one or two small CRT, LCD, LCoS (Liquid Crystal on Silicon), or OLED displays with magnifying lenses embedded in a helmet, glasses or visor. With two displays, the technology can be used to show stereoscopic images by displaying an offset image to each eye. Lenses are used to give the perception that the images are coming from a greater distance, to prevent eye strain. One company, Sensics, makes an HMD with 24 OLED displays, with the lenses designed to combine 12 displays into a seamless image for each eye. Head-mounted displays may also be coupled with head-movement tracking devices to allow the user to "look around" a virtual reality environment naturally by moving the head without the need for a separate controller. Performing this update quickly enough to make the experience immersive requires a great amount of computer image processing. If six axis position sensing (direction and position) is used then the wearer may physically move about and have their movement translated into movement in the virtual environment.

Some head-mounted or wearable glasses may be also be used to view a see-through image imposed upon a real world view, creating what is called augmented reality. This is done by reflecting the video images through partially reflective mirrors. The real world view is seen through the mirrors' reflective surface. Experimental systems have been used for gaming, where virtual opponents may peek from real windows as a player moves about. This type of system has applications in the maintenance of complex systems, as it can give a technician what is effectively "x-ray vision" by combining computer graphics rendering of hidden elements with the technician's natural vision. Additionally, technical data and schematic diagrams may be delivered to this same equipment, eliminating the need to obtain and carry bulky paper documents.

Augmented stereoscopic vision has applications in surgery, as it allows the combination of radiographic data (CAT scans and MRI imaging) with the surgeon's vision. Military, police and firefighters use HMDs to display relevant tactical information such as maps or thermal imaging data. Recently, i-Vue begun manufacturing of a Night Visiion HMD unit. This unit integrates a night vision camera so that the video is directly fed into the goggle to provide real time night vision. Engineers and scientists use HMDs to provide stereoscopic views of CAD schematics, simulations or remote sensing applications. And owing to advancements in computer graphics and the continuing miniaturization of video displays and other equipment, consumer HMD devices are also available for use with 3d games and entertainment.