22-11-2012, 02:38 PM
OPTICAL CAMOUFLAGE
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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. 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. 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 reflective. 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
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 operators 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. 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.
Technology
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.
AUGMENTED REALITY TECHNOLOGY
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. 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. 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 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.
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.
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.
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.