A New Dimension Added to Displays
Anshul Jain and Tarun Sharma, 2nd year B.Tech,
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
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
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:
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