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

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.

Table of contents Chapter Contents Page no. List of Figures ii 1 Introduction 1 1.1 Optical Camouflage- an overvie w 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 Comp uter 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

i

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

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Optical camouflage

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.

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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.

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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.

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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.

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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

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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

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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.

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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.

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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.

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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)

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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

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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.

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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.

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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.

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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.

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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 .

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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CHAPTER – 13

CONCLUSION Invisibility Today... 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 Fig 13.1 The present system of invisibility isn't too bright.

…And Tomorrow

To achieve true invisibility, optical camouflage Fig 13.2 The future of invisibility 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. 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.

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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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