Head-mounted Displays

Just as monitors allow us to see text and graphics generated by computers, head-mounted displays (HMDs) will enable us to view graphics and text created by augmented-reality systems. So far, there haven't been many HMDs created specifically with augmented reality in mind. Most of the displays, which resemble some type of skiing goggles, were originally created for virtual reality. There are two basic types of HMDS:

• video see-through
• optical see-through

Video see-through displays block out the wearer's surrounding environment, using small video cameras attached to the outside of the goggles to capture images. On the inside of the display, the video image is played in real-time and the graphics are superimposed on the video. One problem with the use of video cameras is that there is more lag, meaning that there is a delay in image-adjustment when the viewer moves his or her head.

Photo courtesy Columbia University Computer Graphics and User Interfaces Lab Augmented-reality displays are still pretty bulky; but developers believe that they can create a display that resembles a pair of eyeglasses.

Most companies who have made optical see-through displays have gone out of business. Sony makes a see-through display that some researchers use, called the Glasstron. Blair MacIntyre, director of the Augmented Environments Lab at Georgia Tech, believes that the Microvision's Virtual Retinal Display holds the most promise for an augmented-reality system. This device actually uses light to paint images onto the retina by rapidly moving the light source across and down the retina. The problem with the Microvision display is that it currently costs about $10,000. MacIntyre says that the retinal-scanning display is promising because it has the potential to be small. He imagines an ordinary-looking pair of glasses that will have a light source on the side to project images on to the retina.