A holographic display is a kind of three dimensional display, but unlike the three dimensional effects achieved with traditional three dimensional technologies, it incorporates a true parallax element. This means that the viewer can move around the image in any direction, and the image maintains its integrity. This technology can be used in two ways. It can be used to create a holographic image on a flat display surface that does not actually exist in three dimensions, but appears to, without any special glasses or other viewing aids. A second application is to create a virtual image in space that actually occupies three dimensions and may be viewed from any direction as though it were an actual physical object.
Flat holographic display technology is not new and has been used for decades to create the illusion of three dimensional images on flat surfaces. Like all holographic displays, such an image requires no special glasses or other special equipment to view. It appears as a three dimensional image that appears to rotate in space as the viewer's perspective changes. The most advanced versions of these displays are able to depict three-dimensional versions of aerial maps commonly found on the Internet. When laid on a surface and lighted, the objects and buildings appear to have actual substance, and the viewer can move around the perimeter of the image. Objects and images maintain their perspective regardless of the angle or direction of viewing.
New advances in technology have made possible the true three dimensional holographic display. This technology uses special rotating mirrors and laser projectors to create an image that occupies space in three dimensions, but has no physical substance. A viewer of such a display can move about the object in any direction and the object will maintain its integrity exactly as a real object would. For example, a holographic display of an apple can be viewed in exactly the same way as a real apple on a pedestal. Changing the viewing perspective in any direction will visually result in a perception of the image in exactly the same way as if it were a real object.
Research continues on both versions of this technology. In 2011, researchers at the Massachusetts Institute of Technology (MIT) have also developed an early prototype for a three dimensional holographic television display. This would incorporate existing television technologies to allow three dimensional television that exhibits true image integrity and requires no special glasses. As a viewer changes his position relative to the screen, the holographic display appears to retain its shape and depth, unlike current three dimensional television images, which quickly distort and lose their ability to accurately depict three dimensions when the viewer's perspective moves beyond a critical angle.