by Anton Shilov
12/03/2013 | 11:55 PM
A $500 “nano-camera” that can operate at the speed of light has been developed by researchers in the MIT media lab. The three-dimensional camera, which was presented last month at Siggraph Asia in Hong Kong, could be used in medical imaging and collision-avoidance detectors for cars, and to improve the accuracy of motion tracking and gesture-recognition devices used in interactive gaming.
The camera is based on “Time of Flight” (ToF) technology like that is used in Microsoft’s recently launched second-generation Kinect device, in which the location of objects is calculated by how long it takes a light signal to reflect off a surface and return to the sensor. However, unlike existing devices based on this technology, the new camera is not fooled by rain, fog, or even translucent objects, according to the developers of the project.
“Using the current state of the art, such as the new Kinect, you cannot capture translucent objects in 3-D. That is because the light that bounces off the transparent object and the background smear into one pixel on the camera. Using our technique you can generate 3-D models of translucent or near-transparent objects,” said co-author Achuta Kadambi, a graduate student at MIT.
In a conventional ToF camera, a light signal is fired at a scene, where it bounces off an object and returns to strike the pixel. Since the speed of light is known, it is then simple for the camera to calculate the distance the signal has travelled and therefore the depth of the object it has been reflected from. Unfortunately though, changing environmental conditions, semitransparent surfaces, edges, or motion all create multiple reflections that mix with the original signal and return to the camera, making it difficult to determine which is the correct measurement.
Instead, the new device uses an encoding technique commonly used in the telecommunications industry to calculate the distance a signal has travelled.
MIT students (left to right) Ayush Bhandari, Refael Whyte and Achuta Kadambi pose next to their "nano-camera" that can capture translucent objects, such as a glass vase, in 3-D.
“We use a new method that allows us to encode information in time. So when the data comes back, we can do calculations that are very common in the telecommunications world, to estimate different distances from the single signal,” said Ramesh Raskar, an associate professor of media arts and sciences and leader of the camera culture group within the MIT media lab.
The new model, which the team has dubbed nanophotography, unsmears the individual optical paths. The idea is similar to existing techniques that clear blurring in photographs.
In 2011 Mr. Raskar’s group unveiled a trillion-frame-per-second camera capable of capturing a single pulse of light as it travelled through a scene. The camera does this by probing the scene with a femtosecond impulse of light, then uses fast but expensive laboratory-grade optical equipment to take an image each time. However, this “femto-camera” costs around $500 000 to build.
In contrast, the new “nano-camera” probes the scene with a continuous-wave signal that oscillates at nanosecond periods. This allows the team to use inexpensive hardware – off-the-shelf light-emitting diodes (LEDs) can strobe at nanosecond periods, for example – meaning the camera can reach a time resolution within one order of magnitude of femtophotography while costing just $500.
Conventional cameras see an average of the light arriving at the sensor, much like the human eye. In contrast, the researchers in Mr. Raskar’s laboratory are investigating what happens when they take a camera fast enough to see that some light makes it from the “flash” back to the camera sooner, and apply sophisticated computation to the resulting data.
“Normally the computer scientists who could invent the processing on this data cannot build the devices, and the people who can build the devices cannot really do the computation. This combination of skills and techniques is really unique in the work going on at MIT right now,” said James Davis, an associate professor of computer science at the University of California at Santa Cruz.
What’s more, the basic technology needed for the team’s approach is very similar to that already being shipped in devices such as the new version of Kinect.
“So it’s going to go from expensive to cheap thanks to video games, and that should shorten the time before people start wondering what it can be used for. By the time that happens, the MIT group will have a whole toolbox of methods available for people to use to realize those dreams," concluded Mr. Davis.