83944585 Optical Camouflage
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Transcript of 83944585 Optical Camouflage
ABSTRACT
While new high-performance, light-transmitting materials such as
aerogel and light-transmitting concrete compel us to question the nature of
solidity, a new technology developed by University of Tokyo seeks to make
matter disappear altogether. Scientists at Tachi Laboratory have developed
Optical Camouflage, which utilizes a collection of devices working in concert
to render a subject invisible. Although more encumbering and complicated
than Harry Potter’s invisibility cloak, this system has essentially the same goal,
rendering invisibility by slipping beneath the shining, silvery cloth. Optical
Camouflage requires the use of clothing - in this case, a hooded jacket - made
with a retro-reflective material, which is comprised by thousands of small
beads that reflect light precisely according to the angle of incidence. A digital
video camera placed behind the person wearing the cloak captures the scene
that the individual would otherwise obstruct, and sends data to a computer for
processing. A sophisticated program calculates the appropriate distance and
viewing angle, and then transmits scene via projector using a combiner, or a
half silvered mirror with an optical hole, which allows a witness to perceive a
realistic merger of the projected scene with the background - thus rendering the
cloak-wearer invisible. . The concept of optical camouflage is straight forward
to create the illusion of invisibility by covering an object with something that
projects the scene directly behind that object. This system was conceived with
the primary view in mind of concealing stationary or moving objects such as
men, vehicles, or aircraft from view and has practical military, law
enforcement, and security applications.
1.Introduction
Various methods have been proposed to integrate the visual space. In
the field of Mixed Reality, one of the most popular topics is about displaying a
virtual object into real world However making objects virtually transparent,
like in H.G. Wells’ “Invisible Man” can also be Seen as dream of human being.
In this paper, we describe what could be called a camouflage Technique named
Optical Camouflage.
Camouflage :-
Camouflage is the method which allows an otherwise visible organism or
object to remain indiscernible from the surrounding environment. Examples
include a tiger's stripes and the battledress of a modern soldier. Camouflage is
a form of deception. The word camouflage comes from the French word
'camoufler' meaning 'to disguise'.
Natural camouflage :-
In nature, there is a strong evolutionary pressure for animals to blend into their
environment or conceal their shape; for prey animals to avoid predators and for
predators to be able to sneak up on prey. Natural camouflage is one method
that animals use to meet these aims.
(Anolis caroliensis showing blending camouflage and counter shading.)
Military camouflage :
These were intended to daunt the enemy, attract recruits, foster unit cohesion,
allow easier identification of units in the fog of war.The British in India in
1857 were forced by casualties to dye their red tunics to neutral tones, initially
a muddy tan called khaki.
The United States was quick to follow the British, going khaki in the same
year. Later in 20thcentury, digital camouflage patterns have been
exprerimented on helicopters, battledresses &other vehicles. It is termed
"digital" because much of the design was done on a computer and unlike other
camouflage patterns, it is blocky and appears almost pixelated.
Theory of Camouflage:
MacKay's statement above remains one of the most important elements in the
theory of camouflage - an exact match with the environment's colours is less
crucial than the patterning of the regions of colour themselves. Ideally,
camouflage should be made to break up and thereby conceal the structural lines
of the object which it hides. Thus, the patterns often seen on camouflage
clothing, masking cloth and vehicle paints are carefully constructed to deceive
the human eye by breaking up the boundaries that define sharp edges and
human silhouettes. This is called high difference or disruptive camouflage. This
mix of blending and disruptive patterns is called coincident disruption - the aim
of modern military camouflage.
The opposite of camouflage is making a person or object more visible and
easier to recognize,for example with retroreflectors and high-visibility clothing.
What is Optical Camouflage?
Optical camouflage is a kind of active camouflage. This idea is very simple. If
you project background image onto the masked object, you can observe the
masked object just as if it were virtually transparent. Although optical is a term
that technically refers to all forms of light, most proposed forms of optical
camouflage would only provide invisibility in the visible portion of the
spectrum. The most intriguing prototype uses
an external camera placed behind the cloaked object to record a scene, which it
then transmits to a computer for image processing. The computer feeds the
image into an external projector which projects the image onto a person wearing
a special retroreflective coat. This can lead to different results depending on the
quality of the camera, the projector, and the coat, but by the late nineties,
convincing illusions were created.
The downside is the large amount of external hardware required, along with the
fact that the illusion is only convincing when viewed from a certain angle.
Creating complete optical camouflage across the visible light spectrum would
require a coating or suit covered in tiny cameras and projectors, programmed to
gather visual data from a multitude of different angles and project the gathered
images outwards in an equally large number of different directions to give the
illusion of invisibility from all angles. For a surface subject to bending like a
flexible suit, a massive amount of computing power and embedded sensors
would be necessary to continuously project the correct images in all directions.
This would almost certainly require sophisticated nanotechnology, as our
computers, projectors, and cameras are not yet miniaturized enough to meet
these conditions.
Although the suit described above would provide a convincing illusion to the
naked eye of a human observer, more sophisticated machinery would be
necessary to create perfect illusions in other electromagnetic bands, such as the
infrared band. Sophisticated target-tracking software could ensure that the
majority of computing power is focused on projecting false images in those
directions where observers are most likely to be present, creating the most
realistic illusion possible.
This figure shows the principle of the optical camouflage using X’tal vision.
You can select camouflaged object to cover with retroreflector. Moreover, to
project a stereoscopic image, the observer looks at the masking object more
transparent.
In the above shown figure,This transparent cloak makes you see as if the cloak
is transparent by projecting the shooting image behind the person onto the
cloak i.e. It looks like three men walking behind are seen through the body
of the person. So, actually, the cloak is not really transparent.
How does it work?
First, putting the video camera behind the person in the cloak, and capturing
his background. Then, projecting the captured image onto the cloak from the
projector. So, if you see from the peephole, you will see as if the cloak is
transparent. Because the image is projected by the technology called Retro-
reflective Projection Technology (RPT), you can see the reflection only on
the cloak and clearly even in brightness.
Retro-reflective Projection Technology(RPT):-
Now that we ‘ve seen how does optical camouflage works using RPT &
X’stal vision let us illustrate RPT. When using a See-Through Head-mounted
Display (STHMD) to merge virtual and real environments, the operator may see
the image of a virtual object that is meant to be located behind a real object. This
contradicts our intuition of depth, since the projected image of an object located
behind another object in one's field of view will be obstructed at least partially.
This depth cue is called occlusion, and is critical for the effectiveness of the
presentation of virtual objects in three dimensions. To solve the occlusion
contradiction problem, we developed RPT.
The three key techniques of RPT are the followings:
1-To use an object covered by retro-reflective material as a screen;
2-To place a projector into a position optically conjugated with the observer's eye
by using
a half-mirror;
3-To make the projector's iris as small as possible (by using a pinhole).
Each of these points provides the following advantages, respectively:
Fig.5
Fig 6
Fig.5 and Fig.6 shows the principles of RPT. The image of a virtual object is
projected through a pinhole. The projected image is reflected by the half-mirror
on a right angle and then retro-reflected by the retro-reflective screen.
( no need)
Requirements of an optical camouflage system
The things needed to make a person appear invisible are:
A garment made from highly reflective material
A video camera
A computer
A projector
A special, half-silvered mirror called a combiner
Let's look at each of these components in greater detail.
The Cloak:
The cloak that enables optical camouflage to work is made from a special
material known as retro-reflective material. A retro-reflective material is covered
with thousands and thousands of small beads. When light strikes one of these
beads, the light rays bounce back exactly in the same direction from which they
came. A rough surface creates a diffused reflection because the incident
(incoming) light rays get scattered in many different directions. A perfectly
smooth surface, like that of a mirror, creates what is known as a specular
reflection -- a reflection in which incident light rays and reflected light rays form
the exact same angle with the mirror surface. In retro-reflection, the glass beads
act like prisms, bending the light rays by a process known as refraction.This
causes the reflected light rays to travel back along the same path as the incident
light rays. The result: An observer situated at the light source receives more of
the reflected light and therefore sees a brighter reflection. Retro-reflective
materials are actually quite common. Traffic signs, road markers and bicycle
reflectors all take advantage of retro-reflection to be more visible to people
driving at night. Movie screens used in most modern commercial theaters also
take advantage of this material because it allows for high brilliance under dark
conditions. In optical camouflage, the use of retro-reflective material is critical
because it can be seen from far away and outside in bright sunlight-- two
requirements for the illusion of invisibility.
The Video Camera:
The retro-reflective garment doesn't actually make a person invisible -- in fact,
it's perfectly opaque. What the garment does is create an illusion of invisibility
by acting like a movie screen onto which an image from the background is
projected. Capturing the background image requires a video camera, which sits
behind the person wearing the cloak. The video from the camera must be in a
digital format so it can be sent to a computer for processing.
The Computer:
All augmented-reality systems rely on powerful computers to synthesize
graphics and then superimpose them on a real-world image. For optical
camouflage to work, the hardware/software combo must take the captured
image from the video camera, calculate the appropriate perspective to stimulate
reality and transform the captured image into the image that will be projected
onto the retro-reflective material. The projected image is composed by computer
using animage-based rendering method.
The Projector:
The modified image produced by the computer must be shone onto the
garment, which acts like a movie screen. A projector accomplishes this task
by shining a light beam through an opening controlled by a device called
an iris diaphragm. An iris diaphragm is made of thin, opaque plates, and
turning a ring changes the diameter of the central opening. For optical
camouflage to work properly, this opening must be the size of a pinhole.
Why? This ensures a larger depth of field so that the screen (in this case the
cloak) can be located any distance from the projector.
The Combiner:
The system requires a special mirror to both reflect the projected image
toward the cloak and to let light rays bouncing off the cloak return to the
user's eye. This special mirror is called a beam splitter, or a combiner -- a
half-silvered mirror that both reflects light (the silvered half) and transmits
light (the transparent half). If properly positioned in front of the user's eye,
the combiner allows the user to perceive both the image enhanced by the
computer and light from the surrounding world. This is critical because the
computer-generated image and the real-world scene must be fully integrated
for the illusion of invisibility to seem realistic. The user has to look through a
peephole in this mirror to see the augmented reality.
The Complete System:
Now let's put all of these components together to see how the invisibility
cloak appears to make a person transparent. The diagram below shows the
typical arrangement of all of the various devices and pieces of equipment.
Once a person puts on the cloak made with the retro-reflective material,
here's the sequence of events:
1. A digital video camera captures the scene behind the person wearing
the cloak.
2. The computer processes the captured image and makes the
calculations necessary to adjust the still image or video so it will look
realistic when it is projected.
3. The projector receives the enhanced image from the computer and shines
the image through a pinhole-sized opening onto the combiner.
4. The silvered half of the mirror, which is completely reflective, bounces the
projected image toward the person wearing the cloak.
5. The cloak acts like a movie screen, reflecting light directly back to the
source, which in this case is the mirror.
6.Light rays bouncing off of the cloak pass through the transparent part of the
mirror and fall on the user's eyes. Remember that the light rays bouncing off
of the cloak contain the image of the scene that exists behind the person
wearing the cloak. The person wearing the cloak appears invisible because
the background scene is being displayed onto the retro-reflective material. At
the same time, light rays from the rest of the world are allowed reach the
user's eye, making it seem as if an invisible person exists in an otherwise
normal-looking world.
Inherent Physical Problems With Cloaking An Object :-
• Parametrical design considerations
• Resolution Factors
Parallax, View angle and range dependency, Tilt angle, and Perspective.
• Reflections and Glint
• Parameters were treated in depth by Schowengerdt and Schweizer in 1993 8
- Parallax is most critical and is summarized below and on next page .
• Angular resolution, A, is basically a function of the wavelength, l, and the
diameter, d, of the observer’s aperture (A = l/d ).
• l = 500 nm for the effective central wavelength of visible light
• For human eye, A = 1 minute of arc = 0.0003 radian
• For 10 inch (25 cm) diameter telescope, A = 0.000002 radian
• Minimum range of an object necessary to escape detection is a function of
the observer’s resolution, distance of the object from the observer, the
distance of the object from the background, and lateral motion of the observer
necessary to detect the target.
Real-World Applications:
While an invisibility cloak is an interesting application of optical
camouflage, it's probably not the most useful one. Here are some practical
ways the technology might be applied:
Pilots landing a plane could use this technology to make cockpit floors
transparent. This would enable them to see the runway and the landing gear
simply by glancing down.
Doctors performing surgery could use optical camouflage to see through
their hands and instruments to the underlying tissue. See Tachi Lab: Optical
Camouflage: oc-phantom.mpg to watch a video of how this might work.
Providing a view of the outside in windowless rooms is one of the more
fanciful applications of the technology, but one that might improve the
psychological well-being of people in such environments.
Drivers backing up cars could benefit one day from optical camouflage. A
quick glance backward through a transparent rear hatch or tailgate would make
it easy to know when to stop.
One of the most promising applications of this technology, however, has less to
do with making objects invisible and more about making them visible. The
concept is called mutual telexistence: working and perceiving with the feeling
that you are in several places at once. Here's how it works:
Human user A is at one location while his telexistence robot A is at
another location with human user B.
Human user B is at one location while his telexistence robot B is at
another location with human user A.
Both telexistence robots are covered in retro-reflective material so that
they act like screens.
With video cameras and projectors at each location, the images of the
two human users are projected onto their respective robots in the
remote locations.
This gives each human the perception that he is working with another human
instead of a robot.
Results:
Fig(a) shows the haptic display (real object) hiding the virtual object, but
Optical Camouflage techniques permit to make the haptic display to become
transparent.However, the operator’s hand is not made transparent,which
implies that it is possible to use this technique selectively.
Fig(b) shows a demonstration of ”Invisible Cloak”. It looks as if a red truck
can be seen through the body of a man who wear a retro-reflective coat.
Actually, he does not become transparent perfectly. The shape of the coat
isobserved clearly. Nevertheless, it looks like a very low refractive index
glasswork, which is enough to observe the background.
Fig(a).Optical camouflaged haptic display Fig (b). “Invisible cloak”
Head-mounted Displays:
Of course, making the observer stand behind a stationary combiner is not
very pragmatic -- no augmented-reality system would be of much practical
use if the user had to stand in a fixed location. That's why most systems
require that the user carry the computer on his or her person, either in a
backpack or clipped on the hip. It's also why most systems take advantage of
head-mounted displays, or HMDs, which assemble the combiner and optics in
a wearable device.
There are two types of HMDs: optical see-through displays and video see-
through displays. Optical see-through displays look like high-tech goggles,
sort of like the goggles Cyclops wears in the X-Men comic books and movies.
These goggles provide a display and optics for each eye, so the user sees the
augmented reality in stereo. Video see-through displays, on the other hand,
use video-mixing technology to combine the image from a head-worn camera
with computer-generated graphics.
In this arrangement, video of the real world is mixed with synthesized graphics
and then presented on a liquid-crystal display. The great advantage of video
see-through displays is that virtual objects can fully obscure real-world objects
and vice versa.
HEAD MOUNTED PROJECTOR
Two projectors -- one for each eye -- are required to produce a stereoscopic effect .
Conclusion
We have developed an Optical Camouflage system.Optical Camouflage
can be used on surgical globes or equipments so they don’t block surgeon’s
view during delicate operations. In aviation, cockpit floors couldbecome
'invisible' to assist pilots during landing. The weak point of this technique is
that the observer needs to look through a half-mirror. The current system
needs a half-mirror and projectors, which were fixed onthe ground. In the next
step of our research, an observer would be able to observe the background
image from various viewpoint with H.M.P. (Head-Mounted Projector).