What is Hologram?
Holography is the science and practice of making holograms. Normally, a hologram is a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three-dimensional image of the holographed subject, which is seen without the aid of special glasses or other intermediate optics. The hologram itself is not an image and it is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of seemingly random variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallaxand perspective that change realistically with any change in the relative position of the observer.
In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram. In a side-by-side comparison under optimal conditions, a holographic image is visually indistinguishable from the actual subject, if the hologram and the subject are lit just as they were at the time of recording. A microscopic level of detail throughout the recorded volume of space can be reproduced. In common practice, however, major image quality compromises are made to eliminate the need for laser illumination when viewing the hologram, and sometimes, to the extent possible, also when making it. Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" living subjects as perfectly as the extremely motion-intolerant holographic recording process requires. Holograms can now also be entirely computer-generated and show objects or scenes that never existed.
Holography should not be confused with lenticular and other earlier autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Stage illusions such as Pepper's Ghost and other unusual, baffling, or seemingly magical images are also often incorrectly called holograms.
History of Hologram Technology..
True three dimensional visualisation technologies have been fantasied and theorised about over the past half century. This article talks about the history and the tantalising prospects of finally realising holographic video displays.
Looking Back
Dennis Gabor, a Hungarian scientist working in the UK, presented the foundational concepts of holography in a patent and a series of papers written between 1948 and 1951 that were aimed at microscopy. These introduced the notion of storing the 3D information related to a sample as a 2D interference pattern, containing phase and amplitude information, which can subsequently be reconstructed through illumination. Holography remained somewhat obscure owing to its dependence on coherent light sources. However, things changed radically after the invention of the laser in 1960 when the field had a revival with an upsurge in research and development. Lieth and Upatnieks reached a key milestone with the off-axis transmission hologram. At about the same time, Denisyuk pioneered the reflection hologram. Dennis Gabor was awarded the Physics Nobel Prize in 1971.
Today, the main applications of static holograms are in security and authentication for branding, bank notes, passports etc. Holographic imaging is largely consigned to artistic exhibitions or specialist optical components.
Underground Research
Unfortunately, holography has not lived up to expectations, which were largely driven by the realms of science-fiction fantasy following the iconic Star Wars film in 1977. While static holograms were popular in the 70s and 80s, it soon became clear that static holograms needed to move beyond the lab whereas dynamic holographic displays were "in a land far, far away." Hence, holography went underground in the 1990s with a handful of European companies, some Japanese groups and the U.S. military developing digital hologram printing technology. Holographic display research was mainly performed by military contractors or high-end academic research facilities.
Regarding 3D displays, 3D TV and cinema have come and gone in recent years. This is because conventional stereo 3D is based on glasses or 'glasses-free' lenticular arrays or parallax barriers, leading to a poor 3D experience because it is really just an illusion created by twin-2D images aimed at either eye. This is fundamentally unacceptable to the human brain and leads to all sorts of problems including dizziness and nausea.
3D Content & Data Explosion
The recent proliferation of 3D content has created a demand for such displays due to the explosion of 3D data from many sources including geographical data, medical scans, computer design, simulation, low-cost depth scanners and video gaming. Whereas it is easy to generate 3D content, it has proven very difficult to view this content in real 3D.
A true 3D display should have the scene or object in real space (floating in mid-air), allowing the viewer to look around objects and see them from a slightly different perspective, as they would in real life. This leads to a more comfortable and naturalistic viewing experience without all the problems of stereo 3D. According to the scientific literature, such a display can only be realised with holographic or similar light-field techniques.
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Prof. Jagmeet Brar
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