OPTICAL CAMOUFLAGE Y.Jyothsna Devi S.L.A.Sindhu ¾ B.Tech E.C.E Shri Vishnu engineering college for women Jyothsna.1015@gmail.com sindhu1015@gmail.com Abstract This paper describes a kind of active camouflage system named Optical Camouflage. Initially, Camouflage is made understood and then the theory of optical camouflage is developed. Since the beginning of time, man and all other types of life have used camouflage. It can be used offensively or defensively. Optical Camouflage uses the Retro-reflective Projection Technology, a projection based augmented reality system, composed of a projector with a small iris and a retro reflective screen Optical camouflage using Meta materials. This is accomplished by manipulating the paths traversed by light through an optical material. Optical camouflage is a hypothetical type of active camouflage currently only in a very primitive stage of development. 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. 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 Invisibility has been on human wish list, at least since the advent of fictious idea of invisibility of H.G.Wells. With the recent advances of optics and computing and the recent advents of flexible electronics, such as liquid crystal display, that would allow the back ground image to be displayed on the material itself; however this elusive goal is no longer purely imaginary. Three professors at university of Tokyo created a prototypical camouflage system in which a video camera takes a shot of the back ground and displays it on the cloth using an external projector. It can reflect the images even when the material is wrinkled. It is an application of the optical camouflage and is called the invisibility cloak. This proto type uses an external camera placed behind the cloak to record a scene, which it then transmits to a computer for image processing. The computer feeds the image onto an external
projector which projects the image onto a person wearing a special retro reflective coat. Research is now being carried out to implement this in nanotechnology. 2. Camouflage and active camouflage Camouflage is a method of crypsis (hiding). The word camouflage comes from the French word 'camoufler' meaning 'to disguise'. It allows an otherwise visible organism or object to remain unnoticed, by blending with its environment. The theory of camouflage covers the various strategies which are used to achieve this effect. Examples of camouflage can be seen through the ages. It can evidently be seen in animals and in the military uniforms. The transfer of camouflage patterns from military to exclusive civilian use, is a relatively recent phenomenon. Active camouflage or adaptive camouflage is a group of camouflage technologies which allow an object to blend into its surroundings by use of panels or coatings capable of altering their appearance, color, luminance and reflective properties. Active camouflage has the capacity to provide perfect concealment from visual detection Active camouflage provides concealment in two important ways: firstly, it makes the camouflaged object appear not merely similar to its surroundings, but effectively invisible through the use of mimicry; secondly, active camouflage changes the appearance of the object as changes occur in the background. Ideally, active camouflage mimics nearby objects as well as objects as distant as the horizon. 3. Optical camouflage - An over view: Optical camouflage is a kind of active camouflage which completely envelopes the wearer. It displays an image of the scene opposite the viewer on it so that the viewer can see through the wearer, rendering the wearer invisible. The idea is relatively straight forward: to create the illusion of invisibility by covering the object with something that projects the scene directly behind that object. This would make the object virtually transparent. 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. The most intriguing prototypes of optical camouflage yet have been created by the Tachi Lab at the University of Tokyo, under the supervision of professors Susumu Tachi, Masahiko Inami and Naoki Kawakami. 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 computer feeds the image into an external projector which projects the image onto a person wearing a special retro reflective coat. 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. Creating a truly realistic optical illusion 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. 4. Working of optical camouflage: 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 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 Optical camouflage takes advantage of a technology called augmented reality. The augmented technology is a field of computer research which deals with the combination of real world and computer generated data. The optical camouflage is much to say a mixed reality application. Here the procedure involves a set of apparatus.
4.1. Requirements: A video camera A computer A projector A special, half-silvered mirror called a combiner Video Camera: 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. Computer: All augmented-reality systems rely on powerful computers to synthesize graphics and then superimpose them on a real-world image. For optical camouflage, the Computer must take the image from the video camera; calculate the appropriate perspective to simulate reality to be projected onto the retro-reflective material. Projector: For optical camouflage, the central opening must be the size of a pinhole. This ensures a larger depth of field so that the cloak can be located any distance from the projector. 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. This special mirror is called a beam splitter, or a combiner. The combiner allows the user to perceive both the image enhanced by the computer and light from the surrounding world. 6. REAL WORLD APPLICATIONS: 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. Providing a view of the outside in windowless rooms is one of the more fanciful applications of Optical Camouflage. Drivers backing up cars could benefit one day from optical camouflage. A quick glance backward through a transparent rear would make it easy to know when to stop. 7. Advantages 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 could be made invisible to assist the pilot in landing. 8. Metamaterials cloaking: Metamaterials cloaking is the science of applying metamaterials to achieve invisibilitycloaking. This is accomplished by manipulating the paths traversed by light through an optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and could be utilized to render an object seemingly invisible. Metamaterials cloaking, derived from transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself. 9. Research Other theories of cloaking discuss various science and research based theories for producing an electromagnetic cloak of invisibility. Theories presented employ transformation optics, event cloaking, dipolar scattering cancellation, tunneling light transmittance, sensors and active sources, and sacoustic cloaking. 10. References
[1]http://science.howstuffworks.com/invisibili ty-cloak5.htm [2]http://www.wisegeek.com/what-is-opticalcamouflage.htm [3]http://en.wikipedia.org/wiki/Metamaterial _cloaking [4]http://www.seminarprojects.com/Threadoptical-camouflage-a-seminar-report