Seeing Things As Reflected in Others
“Researchers from Stanford University and Cornell University have put together a projector-camera system that can pull off a classic magic trick: it can read a playing card that is facing away from the camera.
The dual-photography system gains information from a subject by analyzing the way projected patterns of light bounce off it.
The system can show a scene from the point of view of the projector as well as that of the camera. It could eventually be used to quickly add lighting effects in movie scenes, including 
the ability to realistically integrate actors who are shot separately and computer graphics into previously shot scenes.
The work also advances efforts aimed at collecting all of the visual information about a scene by sensing light scattered off objects within it and using the information to create views of the scene from any angle under any lighting condition. The ultimate goal of this area of imaging research is photorealistic virtual reality -- the visual component of the Star Trek holodeck.
The system consists of a digital camera and digital projector. The projector beams a series of black and white pixels at a scene and the camera captures the way the light bounces off objects in the scene. The heart of the system is a computer algorithm that continually monitors the data and changes the patterns in order to gain the needed information. [...]
This allows the researchers to measure the light changes from the projector to the camera, then reverse the light to provide a picture from the point of view of the projector. The method works because the properties of a ray of light are unchanged when the ray is reversed, a characteristic of light termed Helmholtz reciprocity. The trick to reading a playing card that is facing away from the camera is picking up light that is reflected off of a surface behind the card.”
he US military is “developing miniature electronic sensors disguised as rocks that can be dropped from an aircraft and used to help detect the sound of approaching enemy combatants.The devices, which would be no larger than a golf ball, could be ready for use in about 18 months. They use tiny silicon chips and radio frequency identification (RFID) technology that is so sensitive that it can detect the sound of a human footfall at 20ft to 30ft. The project is being carried out by scientists at North Dakota State University, which has licensed nano-technology processes from Alien Technology, a California-based commercial manufacturer of RFID tags for supermarkets. [...] The new sensors would be made cheaply enough to be left on the ground without need for retrieval by soldiers. RFID technology uses radio signals that are sent from a silicon chip to a remote sensing device.”
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