A New Dimension Added to Displays

Anshul Jain and Tarun Sharma, 2nd year B.Tech,

IIIT Allahabad

Moving pictures have fascinated people for glorious centuries. Be it time of bioscopes, when still pictures were slid to make them appear moving, or the time of silent movies, when the dialogues were still being read. Then came the time of talkies and colored moving pictures. Today we have highest resolutions displays that can display any 2D image to greatest extent. This can be marked as the zenith of 2D displays as it is no more as fascinating as it used to be. The new hot topic in this eve is 3D display. Holography explains how.

Holography is a method of virtually producing 3d images. Hologram is a light wave interference pattern recorded on photographic film (or other suitable surface) that can produce a 3-dimensional image when illuminated.

Holograms are not projections. They are not projected. There is no projector. It is simply a piece of film. Light fills up a hologram like plaster would fill up a cast. Technically, they are reconstructions of the light that reflected off the object. When the hologram is illuminated from the original direction of the reference beam, a 3-dimensional image of the object appears where the object was originally. Some holograms must be viewed with laser or monochromatic (single color) light, and others with white light.

The definition is fascinating but the technicality in construction is as simple. A laser beam is split into two beams: {see diagram}.

The reference beam is spread by a lens or curved mirror and aimed directly at the film plate. The object beam is spread and aimed at the object. The object reflects some of the light on the holographic film-plate. The two beams interact forming an interference pattern on the film.

Laser light is needed because it is made of coherent waves (of same wavelength and phase). The principle of holography was discovered in Britain by Dennis Gabor in 1948. He was awarded the Nobel price for this discovery in the early 70's.

Apart from being 3D, the most fascinating thing about holograms is that if it breaks then each broken piece would let you see the image from its own unique perspective. Think of a hologram as a window. Anywhere you look through a window you see what's on the other side. If you were to paint the window black and scratch a hole in the paint on the left side of that window just big enough to look through, you would see everything on the other side of the window. Like looking through a peephole. If you then scratch another viewing peephole somewhere on the right side of the window, you still can see through, but from a different perspective. This is the same effect that each broken piece of a hologram would display. Just remember that if you have two broken pieces taken from opposite sides of the hologram, and you are looking at an object that looks differently from each side, one piece may let you see just one of those sides while the other piece will let you view the other side. So, you might say that each piece of a hologram stores information about the whole image, but from its own viewing angle. No two pieces will give you a view that is exactly the same.

The very next question may be “How the 3D images pop out of the screen when illuminated?” Images that protrude out in front of a piece of holographic film are called real images. Virtual image holograms are used as the masters for real image holograms. Most real image holograms are holograms of holograms. The basic concept is like the idea that a negative of a negative is a positive. In effect, when you typically make a hologram it is orthoscopic (right side out) and virtual (the image appears behind the film). If you turn this orthoscopic and virtual image hologram over the image you see is both pseudoscopic (inside out) and real (in front) since the spatial relationship of where the image is seen has flipped. If you use this image to record a second hologram, that image will be pseudoscopic (inside out) because you are recoding the pseudoscopic image of the first hologram and virtual. If you then turn it over it is orthoscopic (right side out) because an inside out image of an inside out image is right side out and real because each time you flip a hologram over you reverse from virtual image to real image.

TransScreen is an efficient method of implementing 3D viewing. The TransScreen makes it possible for you to create the illusion of large, full color, moving 3D holograms through its unique imaging capabilities. You do not need to wear special glasses.  Front or rear projected video or film images are partially captured by the TransScreen's imaging medium making the projected image clearly visible.  At the same time objects and props behind the TransScreen are also clearly visible giving you a sense of perspective and depth.  The combination of the image apparently floating in the air and your ability to see past the 3D image to view real objects tricks the brain into perceiving 3D.

The TransScreen is comprised of a microscopic pattern of particles suspended in a transparent medium that simultaneously diffracts, reflects and transmits all wavelengths of light.  Through this proprietary process the TransScreen displays a projected image as well as allows you to see beyond the image floating in space.

By putting real objects in front of and behind the video image projected onto the TransScreen surface, the illusion of depth is enhanced.  These "depth cues" help fool the audience into believing that the 2D video image projected onto the TransScreen is a real 3D projection.   Seeing real 3D objects in front and behind the video image gives the brain a subtle but important message that the projected image exists in 3D space with respect to these real objects.

When properly set up, the TransScreen is invisible to the viewer.  The projected image will appear to be floating and moving in empty space.  When projecting your specially shot 2D video onto the TransScreen, the audience will think they are seeing a 3D projection while in actuality they are viewing a 2D video image within a 3D display area.

A unique feature exclusive to the TransScreen is the fact that it is "Polarization Preserving".  This means that the TransScreen can be used for true Stereographic Projection with two video projectors for left eye/right eye 3D projection.   This type of projection differs from normal TransScreen Para-Holographic projection in that viewers wear inexpensive 3D glasses to view two separately polarized video images.  However, in most cases we recommend using the TransScreen with a single projector and no glasses for a more convincing Para-Holographic illusion.  Giving an audience 3D glasses can be like telling them to "pretend" that they are seeing 3D.  An audience viewing a TransScreen Para-Holographic display believes they are seeing a 3D holographic show without any glasses.   TransScreens with polarized stereographic projection are being used by research institutions for true volumetric displays.

Further researches are going on and, who knows, some day we might be able to interact with the images as if they are standing in front of us.