View Full Version : Camera - trillion frames per second

Ron Czapala
12-15-2011, 10:35 PM

It's difficult to imagine how a camera could possibly capture a trillion frames per second. The idea that anything can happen a trillion times in the space of a second is difficult to rationalize, but at the MIT Media Lab they have built a camera that can, and in doing so have redefined slow motion photography.

It's fitting that the evolution of slow motion photography would take place at MIT, where 50 years ago Professor Harold 'Doc' Edgerton revolutionized the technique when he took a famous photograph of a bullet being shot through an apple, a style that's been frequently duplicated since.

The new camera is so fast that it can produce a slow motion video of a burst of light traveling from the length of one-liter water bottle, bounce off the cap and travel back to the bottom of the bottle.

We stopped by the lab of Associate Professor Ramesh Raskar and postdoctoral researcher Andreas Velten, the creators of the camera, to see their work first hand.
This is our final segment in a 6 part series filmed on the campus of MIT. We'd like to thank all the Professors and Researchers that welcomed us into their labs, and to Kimberly Allen from the MIT Press Office.

Bobb Fwed
12-15-2011, 10:51 PM
That is seriously impressive, and mind boggling. Capturing things on camera traveling at the speed of light. Wow.

12-16-2011, 02:49 AM
I had to check the date to make sure it was not April 1st. What kind of image sensor could gather enough light in a trillionth of a second to form an image? Color me somewhat skeptical but willing to be convinced.

Ron Czapala
12-16-2011, 03:07 AM

MIT researchers have created a new imaging system that can acquire visual data at a rate of one trillion exposures per second. That’s fast enough to produce a slow-motion video of a burst of light traveling the length of a one-liter bottle, bouncing off the cap and reflecting back to the bottle’s bottom.

Media Lab postdoc Andreas Velten, one of the system’s developers, calls it the “ultimate” in slow motion: “There’s nothing in the universe that looks fast to this camera,” he says.

The system relies on a recent technology called a streak camera, deployed in a totally unexpected way. The aperture of the streak camera is a narrow slit. Particles of light — photons — enter the camera through the slit and are converted into electrons, which pass through an electric field that deflects them in a direction perpendicular to the slit. Because the electric field is changing very rapidly, it deflects the electrons corresponding to late-arriving photons more than it does those corresponding to early arriving ones.

The image produced by the camera is thus two-dimensional, but only one of the dimensions — the one corresponding to the direction of the slit — is spatial. The other dimension, corresponding to the degree of deflection, is time. The image thus represents the time of arrival of photons passing through a one-dimensional slice of space.

The camera was intended for use in experiments where light passes through or is emitted by a chemical sample. Since chemists are chiefly interested in the wavelengths of light that a sample absorbs, or in how the intensity of the emitted light changes over time, the fact that the camera registers only one spatial dimension is irrelevant.

But it’s a serious drawback in a video camera. To produce their super-slow-mo videos, Velten, Media Lab Associate Professor Ramesh Raskar and Moungi Bawendi, the Lester Wolfe Professor of Chemistry, must perform the same experiment — such as passing a light pulse through a bottle — over and over, continually repositioning the streak camera to gradually build up a two-dimensional image. Synchronizing the camera and the laser that generates the pulse, so that the timing of every exposure is the same, requires a battery of sophisticated optical equipment and exquisite mechanical control. It takes only a nanosecond — a billionth of a second — for light to scatter through a bottle, but it takes about an hour to collect all the data necessary for the final video. For that reason, Raskar calls the new system “the world’s slowest fastest camera (http://web.media.mit.edu/~raskar/trillionfps/).”

Doing the math

After an hour, the researchers accumulate hundreds of thousands of data sets, each of which plots the one-dimensional positions of photons against their times of arrival. Raskar, Velten and other members of Raskar’s Camera Culture group at the Media Lab developed algorithms that can stitch that raw data into a set of sequential two-dimensional images.

The streak camera and the laser that generates the light pulses — both cutting-edge devices with a cumulative price tag of $250,000 — were provided by Bawendi, a pioneer in research on quantum dots: tiny, light-emitting clusters of semiconductor particles that have potential applications in quantum computing, video-display technology, biological imaging, solar cells and a host of other areas.

The trillion-frame-per-second imaging system, which the researchers have presented both at the Optical Society's Computational Optical Sensing and Imaging conference and at Siggraph, is a spinoff of another Camera Culture project, a camera that can see around corners. That camera works by bouncing light off a reflective surface — say, the wall opposite a doorway — and measuring the time it takes different photons to return. But while both systems use ultrashort bursts of laser light and streak cameras, the arrangement of their other optical components and their reconstruction algorithms are tailored to their disparate tasks.

Because the ultrafast-imaging system requires multiple passes to produce its videos, it can’t record events that aren’t exactly repeatable. Any practical applications will probably involve cases where the way in which light scatters — or bounces around as it strikes different surfaces — is itself a source of useful information. Those cases may, however, include analyses of the physical structure of both manufactured materials and biological tissues — “like ultrasound with light,” as Raskar puts it.

As a longtime camera researcher, Raskar also sees a potential application in the development of better camera flashes. “An ultimate dream is, how do you create studio-like lighting from a compact flash? How can I take a portable camera that has a tiny flash and create the illusion that I have all these umbrellas, and sport lights, and so on?” asks Raskar, the NEC Career Development Associate Professor of Media Arts and Sciences. “With our ultrafast imaging, we can actually analyze how the photons are traveling through the world. And then we can recreate a new photo by creating the illusion that the photons started somewhere else.”

“It’s very interesting work. I am very impressed,” says Nils Abramson, a professor of applied holography at Sweden’s Royal Institute of Technology. In the late 1970s, Abramson pioneered a technique called light-in-flight holography, which ultimately proved able to capture images of light waves at a rate of 100 billion frames per second.

But as Abramson points out, his technique requires so-called coherent light, meaning that the troughs and crests of the light waves that produce the image have to line up with each other. “If you happen to destroy the coherence when the light is passing through different objects, then it doesn’t work,” Abramson says. “So I think it’s much better if you can use ordinary light, which Ramesh does.”

Indeed, Velten says, “As photons bounce around in the scene or inside objects, they lose coherence. Only an incoherent detection method like ours can see those photons.” And those photons, Velten says, could let researchers “learn more about the material properties of the objects, about what is under their surface and about the layout of the scene. Because we can see those photons, we could use them to look inside objects — for example, for medical imaging, or to identify materials.”

“I’m surprised that the method I’ve been using has not been more popular,” Abramson adds. “I’ve felt rather alone. I’m very glad that someone else is doing something similar. Because I think there are many interesting things to find when you can do this sort of study of the light itself.”



12-16-2011, 03:02 PM
It looks like a tricked up version of Phils line scanner except this one has a horizontal resolution of 500 sensors that can be sensed @ 1 teraherz.

Ron Czapala
12-16-2011, 04:21 PM
It looks like a tricked up version of Phils line scanner except this one has a horizontal resolution of 500 sensors that can be sensed @ 1 teraherz.

Yeah, for a mere $250,000...


12-16-2011, 05:14 PM
Only Congress can handily exceed a trillion anythings per second, in this case, your hard-earned tax dollars on their bloated budget.

Terahertz? Pishaw. I'm talking TaxaHurts.

12-16-2011, 05:45 PM
I watched the videos and the explanation video. It's a neat concept, but it only works for non-moving subjects. It reminds me of the bullet time special effect. You take many photos of the same scene at slightly different times and then stitch them into a movie. But in their case their cameras only do a single scan line at a time. But the fact that the subject is immobile and their light source is periodic they can stitch separate scan line movies into a full frame movie.

12-16-2011, 06:01 PM
That short pulse of laser light was moving thru the bottle.

Edit: I can't even imagine how much memory it takes to store one second of video.

12-17-2011, 02:15 AM
OK, now that Ron outlined how it's done I am truly impressed by the ingenuity of it.

12-19-2011, 12:28 AM
I read about that. That is crazy. Thanks for posting that video, whoever did that. :)