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The latest milestone in the quest for a Harry Potter-like invisibility cloak has been reached: a way of bending the geometry of space so that light from all directions travels around an object, rather than hitting it. Unable to interact with light, the hidden object is therefore invisible, a new study found. Cloaks of invisibility are relatively rare in folklore; although they do occur in some fairy tales, with optical-camouflage technology the invisibility cloak is already a reality. Design and aesthetic is a powerful tool in getting us to accept new things and ideas. Within art, this can be used in a critical or subversive way. Every period and every technology needs to develop its aesthetics in an organic relation to its own time. Instead of hiding technology we should use the power of design to visualize and express this real world.
reality. While virtual reality aims to replace the world, augmented reality merely tries to supplement it with additional, helpful content. FIG: Augmented-reality displays overlay computer-generated graphics onto the real world. 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:
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. In optical camouflage, the use of retro- reflective material is critical because it can be seen from far away and outside in bright sunlight -- two requirements for the illusion of invisibility.
The 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.
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.
Now let's put all of these components together to see how the invisibility cloak appears to make a person transparent. The diagram below shows the typical arrangement of all of the various devices and pieces of equipment. Once a person puts on the cloak made with the retro-reflective material, here's the sequence of events:
image of the scene that exists behind the person wearing the cloak. The person wearing the cloak appears invisible because the background scene is being displayed onto the retro-reflective material. At the same time, light rays from the rest of the world are allowed reach the user's eye, making it seems as if an invisible person exists in an otherwise normal- looking world.
Of course, making the observer stand behind a stationary combiner is not very pragmatic -- no augmented-reality system would be of much practical use if the user had to stand in a fixed location. That's why most systems require that the user carry the computer on his or her person, either in a backpack or clipped on the hip. It's also why most systems take advantage of head-mounted displays, or HMDs, which assemble the combiner and optics in a wearable device. There are two types of HMDs: optical see- through displays and video see-through displays. Optical see-through displays look like high-tech goggles, sort of like the goggles Cyclops wears in the X-Men comic books and movies. These goggles provide a display and optics for each eye, so the user sees the augmented reality in stereo. Video see-through displays , on the other hand, use video-mixing technology to combine the image from a head-worn camera with computer-generated graphics. FIG: Video see-through display In this arrangement, video of the real world is mixed with synthesized graphics and then presented on a liquid-crystal display. The great advantage of video see-through displays is that virtual objects can fully obscure real-world objects and vice versa. The scientists who have developed optical- camouflage technology are currently perfecting a variation of a video see-through display that brings together all of the
That's because our brains insist on viewing light as having traveled in a straight line, when in fact the water has bent it. Glass does the same thing, which is why telescope lenses make objects appear closer. An invisibility cloak would simply replicate this process in a more sophisticated way.
M. Inami, N. Kawakami, D. Sekiguchi, Y. Yanagida, T. Maeda and S. Tachi. "Visuo- Haptic Display Using Head-Mounted Projector." http://projects.star.t.u- tokyo.ac.jp/projects/MEDIA/xv/oc.html M. Inami, N. Kawakami and S. Tachi. "Optical Camouflage Using Retro-reflective Projection Technology," Proceedings of the Second IEEE and ACM International Symposium on Mixed and Augmented
Reality (ISMAR 03). http://projects.star.t.u- tokyo.ac.jp/projects/MEDIA/xv/oc.html S. Feiner. "Augmented reality: A new way of seeing," Scientific American. April 2002, pp. 48-55. S. Tachi. "Telexistence and Retro- reflective Projection Technology (RPT)," Proceedings of the 5th Virtual Reality International Conference (VRIC2003), pp. 69/1-69/9. http://projects.star.t.u- tokyo.ac.jp/projects/MEDIA/xv/oc.html
