Optical Camouflage

OPTICAL CAMOUFLAGE

A SEMINAR REPORT

Submitted by

SUDEESH S

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGY

in

COMPUTER SCIENCE AND ENGINEERING

SCHOOL OF ENGINEERING

COCHIN UNIVERSITY OF SCIENCE &TECHNOLOGY,

KOCHI-682022

AUGUST 2008

DIVISION OF COMPUTER SCIENCE AND

ENGINEERING

SCHOOL OF ENGINEERING

COCHIN UNIVERSITY OF SCIENCE &

TECHNOLOGY, COCHIN-682022

Bonafide Certificate Bonafide Certificate Bonafide Certificate Bonafide Certificate

Certified that this is a bonafide record of the Seminar Entitled

“Optical Camouflage”

Done by

SUDEESH S

Of VIIth semester, Computer Science and Engineering in the year 2008 in

partial fulfillment of the requirements to the award of Degree Of Bachelor

Of Technology in Computer Science and Engineering of Cochin University

of Science and Technology.

Ms. Sheena S. Dr. David Peter

Seminar Guide Head of Department

Date:

ACKNOWLEDGEMENT

At the outset, I thank the Lord Almighty for the grace, strength and

hope to make my endeavor a success.

I also express my gratitude to Dr. David Peter, Head of the

Department and my Seminar Guide for providing me with adequate

facilities, ways and means by which I was able to complete this seminar. I

express my sincere gratitude to him for his constant support and valuable

suggestions without which the successful completion of this seminar would

not have been possible.

I thank Ms.Sheena S, my seminar guide for her boundless

cooperation and helps extended for this seminar. I express my immense

pleasure and thankfulness to all the teachers and staff of the Department of

Computer Science and Engineering, CUSAT for their cooperation and

support.

Last but not the least, I thank all others, and especially my classmates

and my family members who in one way or another helped me in the

successful completion of this work.

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.

i

Table of contents

Chapter Contents Page no.

1

List of Figures

Introduction

ii

1

1.1 Optical Camouflage- an overview 2

2 Technology Focus 3

3 Altered Reality 4

4 Block Diagram 7

4.1 Description 7

4.2 Working 8

5 Retro reflectivity 9

6 Video Camera & Projector 16

6.1 Video Camera 16

6.2 Projector 17

7 Computer and Combiner 18

7.1 Computer 18

7.2 Combiner 18

8 Flowchart 19

9 Head Mounted Display 21

10 Real World Applications 23

11 Drawbacks 26

12 Future Enhancements 27

13 Conclusion 28

14 References 29

ii

LIST OF FIGURES

Page No.

Figure 3.1 Display of GPS 4

Figure 3.2 Relation of Different Environment 5

Figure 3.3 Monitor Based Augmented Reality 5

Figure 3.4 Components of Augmented Reality 6

Figure 4.1 Block Diagram 7

Figure 5.1 Surface Reflectivity 10

Figure 5.2 Retro Reflective Material 11

Figure 8.1 Complete System 20

Figure 9.1 Head Mounted Display 21

Figure 10.1 Mutual Telexistence 25

Figure 12.1 Adaptive Camouflage 27

Figure 12.2 Combat Aircraft 27

Figure 13.1 Present System of Invisibility 28

Figure 13.2 Future of Invisibility 28

Optical camouflage

Division Of Computer Engineering, SOE, CUSAT -1-

CHAPTER - 1

INTRODUCTION

Invisibility has been on humanity's wish list at least since Amon-Ra, a deity who

could disappear and reappear at will, joined the Egyptian pantheon in 2008 BC. With

recent advances in optics and computing and with the advent of flexible electronics such

as a flexible liquid crystal display, that would allow the background image to be

displayed on the material itself, however, this elusive goal is no longer purely imaginary.

In 2003, three professors at University of Tokyo — Susumu Tachi, Masahiko

Inami and Naoki Kawakami — created a prototypical camouflage system in which a

video camera takes a shot of the background and displays it on the cloth using an external

projector. They can even reflect images when the material is wrinkled. The same year

Time magazine named it the coolest invention of 2003. It is an interesting application of

optical camouflage and is called the Invisibility Cloak. Through the clever application of

some dirt-cheap technology, the Japanese inventor has brought personal invisibility a step

closer to reality.

Their 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 key

development of the cloak, however, was the development of a new material called retro-

reflectum. Professor Tachi says that this material allows you to see a three-dimensional

image. The computer feeds the image into an external projector which projects the image

onto a person wearing a special retro reflective 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. That was only one invention created in this

field and researches are still being carried out in order to implement it using

nanotechnology.

Optical camouflage


1.1 OPTICAL CAMOUFLAGE – AN OVERVIEW

Optical camouflage is a kind of active camouflage which completely envelopes

the wearer. It displays an image of the scene on the side opposite the viewer on it, so that

the viewer can "see through" the wearer, rendering the wearer invisible. The idea is

relatively straightforward: to create the illusion of invisibility by covering an object with

something that projects the scene directly behind that object. If you project background

image onto the masked object, you can observe the masked object just as if it were

virtually transparent.

Optical camouflage can be applied for a real scene. In the case of a real scene, a

photograph of the scene is taken from the operator’s viewpoint, and this photograph is

projected to exactly the same place as the original. Actually, applying HMP-based optical

camouflage to a real scene requires image-based rendering techniques.

As for camouflage, it means to blend with the surroundings. 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'. The camouflage technique of

disguise is not as common as coloration, but can be found throughout nature as well.

Animals may disguise themselves as something uninteresting in the hopes that their

predators will ignore them or as something dangerous so that predators will avoid them.

And so had humans the desire to disguise themselves just as some animals could do. 19th

century armies tended to use bright colors and bold, impressive designs. These were

intended to daunt the enemy, attract recruits, foster unit cohesion, or allow easier

identification of units in the fog of war. The transfer of camouflage patterns from battle to

exclusively civilian uses is a recent phenomenon. The concept of camouflage - to conceal

and distort shapes - is also a popular artistic tool.

Optical camouflage


CHAPTER -2

TECHNOLOGY FOCUS

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. Optics (appearance or look in ancient Greek) is a branch of

physics that describes the behavior and properties of light and the interaction of light with

matter. Optics explains optical phenomena. The pure science aspects of the field are often

called optical science or optical physics.

This technology is currently only in a very primitive stage of development.

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.

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 would likely require Phase Array Optics, which

would project light of a specific amplitude and phase and therefore provide even greater

levels of invisibility. We may end up finding optical camouflage to be most useful in the

environment of space, where any given background is generally less complex than

earthly backdrops and therefore easier to record, process, and project.

Optical camouflage


CHAPTER – 3

ALTERED REALITY

Optical camouflage doesn't work by way of magic. It works by taking

advantage of something called augmented-reality technology -- a type of technology

that was first pioneered in the 1960s by Ivan Sutherland and his students at Harvard

University and the University of Utah. Augmented reality (AR) is a field of computer

research which deals with the combination of real world and computer generated

data.

Fig 3.1 Display of GPS (which is an augmented reality system)

The above is an example of how it looks like when viewed through the display of

augmented reality system.

Optical camouflage


At present, most AR research is concerned with the use of live video imagery

which is digitally processed and "augmented" by the addition of computer generated

graphics. Advanced research includes the use of motion tracking data, fiducial marker

recognition using machine vision, and the construction of controlled environments

containing any number of sensors and actuators.

Fig 3.2 Relation of different environments

The real world and a totally virtual environment are at the two ends of this

continuum with the middle region called Mixed Reality. Augmented reality lies near

the real world end of the line with the predominate perception being the real world

augmented by computer generated data. Augmented virtuality is a term created by

Milgram(Milgram and Kishino 1994; Milgram, Takemura et al. 1994) to identify

systems which are mostly synthetic with some real world imagery added such as

texture mapping video onto virtual objects. This is a distinction that will fade as the

technology improves and the virtual elements in the scene become less

distinguishable from the real ones.

Fig 3.3 Monitor Based Augmented Reality

Optical camouflage


Most augmented-reality systems require that users look through a special

viewing apparatus to see a real-world scene enhanced with synthesized graphics.

They also require a powerful computer.

In augmented reality, the scene is viewed by an imaging device, which in

this case is depicted as a video camera. The camera performs a perspective projection

of the 3D world onto a 2D image plane. The intrinsic(focal length and lens distortion)

and extrinsic(position and pose)parameters of the device determine exactly what is

projected onto its image plane. The generation of the virtual image is done with a

standard computer graphics system. The virtual objects are modeled in an object

reference frame. The graphics system requires information about the imaging of the

real scene so that it can correctly render these objects. This data will control the

synthetic camera that is used to generate the image of the virtual objects. This image

is then merged with the image of the real scene to form the augmented reality image.

Fig 3.4 Components of an Augmented Reality System

Optical camouflage


CHAPTER – 4

BLOCK DIAGRAM

Fig 4.1 Block Diagram

4.1 DESCRIPTION

Optical camouflage works by taking advantage of something called augmented-

reality technology -- a type of technology that was first pioneered in the 1960s by Ivan

Sutherland and his students at Harvard University and the University of Utah.

Augmented-reality systems add computer-generated information to a user's sensory

perceptions. Imagine, for example, that you're walking down a city street. As you gaze at

sites along the way, additional information appears to enhance and enrich your normal

view. Perhaps it's the day's specials at a restaurant or the show times at a theater or the

bus schedule at the station. What's critical to understand here is that augmented reality is

not the same as virtual reality. While virtual reality aims to replace the world, augmented

reality merely tries to supplement it with additional, helpful content.

Optical camouflage


Most augmented-reality systems require that users look through a special viewing

apparatus to see a real-world scene enhanced with synthesized graphics. They also

require a powerful computer.

Optical camouflage requires these things, as well, but it also requires several other

components. Here's everything needed to make a person appear invisible:

• A garment made from highly reflective material

• A video camera

• A computer

• A projector

• A special, half-silvered mirror called a combiner

4.2 WORKING

For using optical camouflage, the following steps are to be followed –

1) The person who wants to be invisible (let's call her Person A) dons a garment that

resembles a hooded raincoat. The garment is made of a special material that we'll

examine more closely in a moment.

2) An observer (Person B) stands before Person A at a specific location. At that

location, instead of seeing Person A wearing a hooded raincoat, Person B sees

right through the cloak, making Person A appear to be invisible.

Optical camouflage


CHAPTER- 5

RETROREFLECTIVITY

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.

To understand why this is unique, look at how light reflects off of other types of

surfaces. 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.

A retro reflector is a device that sends light or other radiation back where it

came from regardless of the angle of incidence, unlike a mirror, which does that only if

the mirror is exactly perpendicular to the light beam. Retro reflectors are clearly visible in

a pair of bicycle shoes. Light source is a flash a few centimeters above camera lens.

Optical camouflage


Fig 5.1 Surface Reflectivity (of various kinds of surfaces)

This effect can be commonly obtained in two ways:

1.) With reflecting and refracting optical elements arranged so that the focal surface

of the refractive element coincides with the reflective surface, typically a

transparent sphere and a spherical mirror - this same effect may be achieved with

a single transparent sphere provided that the refractive index of the material is

exactly 2 times the refractive index of the medium from which the radiation is

incident. In that case, the sphere surface behaves as a concave spherical mirror

with the required curvature for retro reflection. This is conventionally known as a

cat's eye retro reflector in either configuration.

2.) With a set of three mutually perpendicular mirrors which form a corner (a corner

reflector or corner cube)

Optical camouflage


Fig 5.2 Reflectivity of a retro reflective material

Corner retro reflectors occur in two varieties. In the more common form, the

corner is literally the truncated corner of a cube of transparent material such as

conventional optical glass. In this structure, the reflection is achieved either by total

internal reflection or silvering of the outer cube surfaces. The second form uses mutually

perpendicular flat mirrors bracketing an air space. These two types have similar optical

properties.

A retro reflector may consist of many very small versions of these structures

incorporated in a thin sheet or in paint. In the case of paint containing glass beads, the

paint glues the beads to the surface where retro reflection is required, and the beads

protrude, their diameter being about twice the thickness of the paint.

The term cat's eye derives from the resemblance of the cat's eye retro reflector to

the optical system that produces the well-known phenomenon of "glowing eyes" in cats

Optical camouflage


and many other vertebrates (which are of course only reflecting light, rather than actually

glowing). The combination of the eye's lens and the aqueous humor form the refractive

converging system, while the tapetum lucidum behind the retina forms the spherical

concave mirror. Because the function of the eye is to form an image on the retina, an eye

focused on a distant object has a focal surface that approximately follows the reflective

tapetum lucidum structure, which is the condition required to form a good retro

reflection.

A third, much less common way of producing a retro reflector is to use the

nonlinear optical phenomenon of phase conjugation. This technique is used in advanced

optical systems such as high-power lasers and optical transmission lines. Phase conjugate

mirrors require a comparatively expensive and complex apparatus, as well as large

quantities of power (as nonlinear optical processes are generally not very efficient).

However, they have an inherently much greater accuracy in the direction of the retro

reflection, which in passive elements is limited by the mechanical accuracy of the

construction.

1.) RETRO REFLECTORS ON ROAD

Retro reflection (sometimes called retroflection) is used on road surfaces, road

signs, vehicles and clothing (large parts of the surface of special safety clothing, less on

regular coats). When the headlights of a car illuminate a retro reflective surface, the

reflected light is directed towards the car and its driver, and not wasted by going in all

directions as with diffuse reflection. However, a pedestrian can see a retro reflective

surface in the dark only if there is a light source directly between them and the reflector,

e.g. a torch they carry, or directly behind them, e.g. a car approaching from behind. "Cat's

eyes" are a particular type of retro reflector embedded in the road surface.

Optical camouflage


Corner reflectors are better at sending the light back to the source over long

distances, while spheres are better at sending the light to a receiver somewhat off-axis

from the source, as when the light from headlights is reflected into the driver's eyes.

Retro reflectors can be embedded in the road leveled with or can be raised above

the road surface. Raised reflectors are visible for a very long distance (typically 0.5-1

kilometer or more), while sunken reflectors are only visible at very close range due to the

higher angle required to properly reflect the light. Raised reflectors are not generally used

in areas that regularly experience snow during winter, as passing snowplows will tear

them off the roadway. The stress on the roadway caused by cars running over any

embedded objects also contributes to accelerated wear and pothole formation.

Retro reflective road paint is thus very popular in Canada and increasingly the

northern parts of the United States, as it is not affected by the passage of snowplows and

does not affect the interior of the roadway. Where weather permits, embedded retro

reflectors are preferred as they last much longer than road paint, which is weathered by

the elements and ground away by the passage of vehicles.

2.) RETROREFLECTORS ON MOON

The Apollo 11, 14, and 15 missions left retro-reflectors on the Moon as part of the

Lunar Laser Ranging Experiment. They are considered to be one of the strongest pieces

of evidence against a Moon landing hoax. Additionally the unmanned Soviet Lunokhod 1

and Lunokhod 2 rovers carried smaller arrays. Reflected signals were initially received

from Lunokhod 1, but no return signals have been detected since 1971, at least in part due

to some uncertainty in its location on the Moon. Lunokhod 2's array continues to return

signals to Earth. Even under good viewing conditions, only a single reflected photon is

received every few seconds. This makes the job of filtering laser-generated photons from

naturally-occurring photons challenging.

Optical camouflage


3.) RETROREFLECTORS USED IN MOTORCYCLE SAFETY

Conspicuity or visibility as outlined by The Motorcycle Safety Foundation greatly

increases a motorcyclist's chances of being seen by motorists at night. Placing retro

reflective patches on clothing and helmets greatly increases the visibility of bikers and

pedestrians to oncoming motorists.

Many materials appear to have some small degree of reflectivity, but retro

reflective materials bounce the greatest amount of light back toward a light source. This

makes them startlingly visible in dark conditions. Some patches claim to be reflective,

but only retro reflective materials can be seen from more than a few feet away at night.

Retro reflectivity is measured in candle power. Official data says that white clothing

performs up to 0.3 candle power. A vehicle license plate comes in at a level of 50. A

conforming retro-reflective material has 500 candle powers! There is a direct relationship

between reflective index (candle power),and the distance from which it can be seen.

4.) RETROREFLECTORS AND INVISIBILITY

Retro reflective clothing, combined with a properly set up camera and projector,

can be used to achieve the effect of partial invisibility when viewed from a one direction.

5.) RETROREFLECTORS IN EARTH ORBIT

LAGEOS, or Laser Geodynamics Satellites, are a series of scientific research

satellites designed to provide an orbiting laser ranging benchmark for geodynamical

studies of the Earth. There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976,

and LAGEOS-2 launched in 1992.

Optical camouflage


6.) RETROREFLECTORS AND COMMUNICATIONS

Modulated retro reflectors, in which the reflectance is changed over time by some

means, are the subject of research and development for free-space optical

communications networks. The basic concept with such systems is that a low-power

remote system, such as a sensor mote, can receive an optical signal from a base station

and reflect the modulated signal back to the base station. Since the base station supplies

the optical power, this allows the remote system to communicate without excessive

power consumption. Modulated retro reflectors also exist in the form of modulated

phase-conjugate mirrors (PCMs). In the latter case, a "time-reversed" wave is generated

by the PCM, with temporal encoding of the phase-conjugate wave.

Cheap plastic corner retro reflectors are using as an aiming device in user-

controlled technology optical data link device Ronja. The aiming is done in night and the

necessary retro reflector area depends on aiming distance and ambient lighting from

street lamps. The optical receiver itself behaves as a weak retro reflector, because

contains a large precisely focused lens and shiny object in the focal plane. This allows

aiming without a retro reflector for short range.

7.) RETROREFLECTVITY USED TO DETECT DIGITAL CAMERAS

The sensor system of common (non-SLR) digital cameras is retro reflective.

Researchers have used this property to demonstrate a system to prevent unauthorized

photographs by detecting digital cameras and beaming a highly-focused beam of light

into the lens.

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.

Optical camouflage


CHAPTER – 6

VIDEO CAMERA AND PROJECTOR

6.1 VIDEO CAMERA

Professional video camera (often called a Television camera even though the use

has spread) is a high-end device for recording electronic moving images (as opposed to a

movie camera that records the images on film). Originally developed for use in television

studios, they are now commonly used for corporate and educational videos, music videos,

direct-to-video movies, etc. Less advanced video cameras used by consumers are often

referred to as camcorders.

There are two types of professional video cameras: High end portable, recording

cameras (which are, confusingly, called camcorders too) used for ENG image acquisition,

and studio cameras which lack the recording capability of a camcorder, and are often

fixed on studio pedestals. It is common for professional cameras to split the incoming

light into the three primary colors that humans are able to see, feeding each color into a

separate pickup tube (in older cameras) or charge-coupled device (CCD). Some high-end

consumer cameras also do this, producing a higher-quality image than is normally

possible with just a single video pickup.

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.

Optical camouflage


6.2 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.

In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its

centre. The role of the diaphragm is to stop the passage of light, except for the light

passing through the aperture. Thus it is also called a stop (an aperture stop, if it limits the

brightness of light reacting the focal plane, or a field stop or flare stop for other uses of

diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective,

and the size of the aperture regulates the amount of light that passes through the lens. The

centre of the diaphragm's aperture coincides with the optical axis of the lens system.

Most modern cameras use a type of adjustable diaphragm known as an iris

diaphragm, and often referred to simply as an iris.

The number of blades in an iris diaphragm has a direct relation with the

appearance of the blurred out-of-focus areas in an image, also called Bokeh. The more

blades a diaphragm has, the rounder and less polygon-shaped the opening will be. This

results in softer and more gradually blurred out-of-focus areas.

Optical camouflage


CHAPTER - 7

COMPUTER AND COMBINER

7.1 COMPUTER

A computer is a machine for manipulating data according to a list of instructions.

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 simulate reality and transform the captured image into the

image that will be projected onto the retro-reflective material.

Image-based rendering techniques are used. Actually, applying HMP-based

optical camouflage to a real scene requires image-based rendering techniques.

7.2 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.

Optical camouflage


CHAPTER – 8

FLOWCHART

Sequence of events once a person puts on the cloak with the retro-reflective material:

A digital video camera captures the scene behind the person wearing the cloak.

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.

The projector receives the enhanced image from the computer and shines the image

through a pinhole-sized opening onto the combiner.

The silvered half of the mirror, which is completely reflective, bounces the projected

image toward the person wearing the cloak.

The cloak acts like a movie screen, reflecting light directly back to the source, which

in this case is the mirror.

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.

Optical camouflage


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 seems as if an invisible

person exists in an otherwise normal-looking world.

Fig 8.1 The complete system of an Invisibility Cloak

Optical camouflage


CHAPTER – 9

HEAD MOUNTED DISPLAY

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.

Fig 9.1 A head mounted display

A head-mounted display (HMD) is a display device that a person wears on the

head to have video information directly displayed in front of the eyes.

Short for head-mounted display, a headset used with virtual reality systems. An

HMD can be a pair of goggles or a full helmet. In front of each eye is a tiny monitor.

Because there are two monitors, images appear as three-dimensional. In addition, most

HMDs include a head tracker so that the system can respond to head movements. For

example, if you move your head left, the images in the monitors will change to make it

seem as if you're actually looking at a different part of the virtual reality.

Optical camouflage


An HMD has either one or two small CRT, LCD, LCoS (Liquid Crystal on

Silicon), or OLED displays with magnifying lenses embedded in a helmet, glasses or

visor. With two displays, the technology can be used to show stereoscopic images by

displaying an offset image to each eye. Lenses are used to give the perception that the

images are coming from a greater distance, to prevent eye strain. One company, Sensics,

makes an HMD with 24 OLED displays, with the lenses designed to combine 12 displays

into a seamless image for each eye. Head-mounted displays may also be coupled with

head-movement tracking devices to allow the user to "look around" a virtual reality

environment naturally by moving the head without the need for a separate controller.

Performing this update quickly enough to make the experience immersive requires a great

amount of computer image processing. If six axis position sensing (direction and

position) is used then the wearer may physically move about and have their movement

translated into movement in the virtual environment.

Some head-mounted or wearable glasses may be also be used to view a see-

through image imposed upon a real world view, creating what is called augmented

reality. This is done by reflecting the video images through partially reflective mirrors.

The real world view is seen through the mirrors' reflective surface. Experimental systems

have been used for gaming, where virtual opponents may peek from real windows as a

player moves about. This type of system has applications in the maintenance of complex

systems, as it can give a technician what is effectively "x-ray vision" by combining

computer graphics rendering of hidden elements with the technician's natural vision.

Additionally, technical data and schematic diagrams may be delivered to this same

equipment, eliminating the need to obtain and carry bulky paper documents.

Military, police and firefighters use HMDs to display relevant tactical information

such as maps or thermal imaging data. Engineers and scientists use HMDs to provide

stereoscopic views of CAD schematics, simulations or remote sensing applications. And

owing to advancements in computer graphics and the continuing miniaturization of video

displays and other equipment, consumer HMD devices are also available for use with 3d

games and entertainment.

Optical camouflage


CHAPTER – 10

REAL WORLD APPLICATIONS

While an invisibility cloak is an interesting application of optical camouflage,

there are also some other practical ways the technology might be applied:

1. AUGMENTED STEREOSCOPIC VISION IN SURGERY

It allows the combination of radiographic data (CAT scans and MRI imaging)

with the surgeon's vision. Doctors performing surgery could use optical camouflage to

see through their hands and instruments to the underlying tissue, thereby making the

complicated surgeries a bit better. Surgeons may not need to make large incisions if they

wear gloves that project what's on the inside of a patient using a CAT scan or MRI data.

2. COCKPIT FLOORS

Pilots landing a plane could use this technology to make cockpit floors transparent

with micro reflectors. This would enable them to see the runway and the landing gear

simply by glancing down. Hard landings would be a thing of the past if pilots could

gauge how far they are above the ground just by looking at an image of the outside

terrain projected on the floor. This allows them to avoid many obstacles on the path

below and be aware of the floor below them thereby creating a complete awareness.

3. TRANSPARENT REAR HATCH

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.

Optical camouflage


4. WINDOWLESS ROOMS

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.

5. STEALTH TECHNOLOGY

Stealth means ‘low observable’. The very basic idea of Stealth Technology in the

military is to ‘blend’ in with the background. The applications of stealth technology are

mainly military oriented.

Stealth Technology is used in the construction of mobile military systems

such as aircrafts and ships to significantly reduce their detection by enemy, primarily

by an enemy RADAR. The way most airplane identification works is by constantly

bombarding airspace with a RADAR signal. When a plane flies into the path of the

RADAR, a signal bounces back to a sensor that determines the size and location of the

plane. Other methods focus on measuring acoustic (sound) disturbances, visual contact,

and infrared signatures. The Stealth technology works by reducing or eliminating these

telltale signals. Panels on planes are angled so that radar is scattered, so no signal returns.

The idea is for the radar antenna to send out a burst of radio energy, which is

then reflected back by any object it happens to encounter. The radar antenna measures

the time it takes for the reflection to arrive, and with that information can tell how far

away the object is. The metal body of an airplane is very good at reflecting radar signals,

and this makes it easy to find and track airplanes with radar equipment.

The goal of stealth technology is to make an airplane invisible to radar. There are

two different ways to create invisibility:

• The airplane can be shaped so that any radar signals it reflects are reflected away

from the radar equipment.

• The airplane can be covered in materials that absorb radar signals.

Optical camouflage


6. MUTUAL TELEXISTENCE

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. Real-time video of two or more distance separated individuals is projected

onto surrogate robotic participants via sophisticated communication technology.

1. Human user A is at one

location while his

telexistence robot A is at

another location with

human user B.

2. Human user B is at one

location while his

telexistence robot B is at

another location with

human user A.

3. Both telexistence robots

are covered in retro-

reflective material so that

they act like screens.

4. 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.

5. This gives each human the

perception that he is

working with another

Fig 10.1 Telexistence human instead of a robot.

Optical camouflage


CHAPTER – 11

DRAWBACKS

• Large amount of external hardware required –

For the invisibility cloak to work properly, we need a number of components such

as a video camera (which sits behind the person wearing the cloak and captures the

background image.), a computer (which takes the captured image from the video camera,

calculate the appropriate perspective to simulate reality and transform the captured image

into the image that will be projected onto the retro-reflective material), a projector (which

takes the modified image produced by the computer and shines it onto the garment,

which acts like a movie screen), an iris diaphragm (The projector sends the light through

the iris diaphragm, which is actually a small opening), a combiner (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), and most importantly a retro reflective cloak (which has

special reflecting properties) to cover the object which needs to be made invisible.

• The illusion is only convincing when viewed from a certain angle -

The Invisibility cloak that we have in hand at present appears to be invisible only

from one point of view. But a real invisibility cloak, if it's going to dupe anyone who

might see it, needs to represent the scene behind its wearer accurately from any angle.

Moreover, since any number of people might be looking through it at any given moment,

it has to reproduce the background from all angles at once. That is, it has to project a

separate image of its surroundings for every possible perspective.

Optical camouflage


CHAPTER – 12

FUTURE ENHANCEMENTS

There are many technology gaps to bridge to reach true invisibility. Our eyes are

only the raw photo sensors that deliver basic electrochemical signals to our brain, which

then processes these low-level cues into higher cognition notions. Thus, it might be

possible to think of invisibility at the human brain level. This is called cognitive

blindness which could be individually selective compared with real world, physics based

absolute invisibility. We see using the persistence of vision property. Light is first

accumulated in retinal photo sensors (cones and rods) before propagating the impulses

into electrochemical reactions. Thus, we average light, and this causes various scene

aliasing effects. Thus vibration and light averaging might also be a future direction for

finding other invisibility tricks. Adaptive camouflage technology could one day allow

soldiers to take a picture of their surroundings and digitally transfer the image using a

handheld computer to the surface of their clothing.

Fig 12.1 Adaptive Camouflage

Fig 12.2 An insight into the future - a future combat aircraft with both stealth and active camouflage

technology.

Optical camouflage


CHAPTER – 13

CONCLUSION

Invisibility Today...

Fig 13.1 The present system of invisibility

…And Tomorrow

Fig 13.2 The future of invisibility

The cameras will transmit images to a dense array of display

elements, each capable of aiming thousands of light beams on their own individual

trajectories. These elements project a virtual scene derived from the cameras' views,

making it possible to synthesize various perspectives.

In Susumu Tachi's cloaking system, a

camera behind the wearer feeds

background images through a computer to

a projector, which paints them on a jacket

as though it were a movie screen. The

wearer appears mysteriously translucent -

as long as observers are facing the

projection head-on and the background

isn't too bright.

To achieve true invisibility, optical camouflage

must capture the background from all angles and

display it from all perspectives simultaneously.

This requires a minimum of six stereoscopic

camera pairs, allowing the computer to model the

surroundings and synthesize the scene from every

point of view. To display this imagery, the fabric

is covered with hyper pixels, each consisting of a

180 x 180 LED array behind a hemispherical lens.

Optical camouflage


CHAPTER – 14

REFERENCES

1) M. Shiro, Ghost in the Shell, Kodansya, 1991

2) http://www.star.t.u-tokyo.ac.jp

3) http://en.wikipedia.org/wiki/Cloaking_device

4) http://en.wikipedia.org/wiki/Active_camouflage

5) http://www.wisegeek.com/what-is-optical-camouflage.htm

6) http://objsam.wordpress.com/2008/01/30/japanese-invisible-technology-optical-

camouflage

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Optical Camouflage