Understanding Trillion Frames-per-Second Video
In the 1960s, MIT professor Harold “Doc” Edgerton, the pioneer of stop-action photography, demonstrated his invention via the famous 1964 photo of a bullet piercing an apple. The picture was taken with an exposure of a million frames per second. Inspired by Edgerton’s work, some fifty years later researchers at MIT’s Media Lab embarked upon a mission to create a new imaging system that can acquire visual data at a rate of one trillion exposures per second, photographing light as it moves. In December 2011, they announced their success.
The process is called femto-photography. It creates slow-motion videos of light in motion, and the camera is called the femto-camera. The first images the MIT team released showed images of light beams sweeping over an apple, and from the bottom to the top of a soda bottle.
While the practical application of this technology by Atlanta’s leading video production company is a way down the line, this is a significant step forward in photography and video, and one worth exploring.
How Does Femto-Photography Work?
The imaging technology is based on that used in a streak camera or streak tubes, which measure the variation in a pulse of light’s intensity with time. The repeated laser pulses simulate a moving image. The streak camera is used by chemists in experiments where light passes through or is emitted by a chemical sample.
The femto-photography process uses a laser combined with engineering and optical techniques to snap thousands of images. Instead of a round lens, the camera has a slit, where light passes through and encounters an electric field that’s changing rapidly, deflecting the light particles, or photons. The protons 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.
A sensor inside the camera captures the photons one slit a time. Each “slice of photons” is then combined into one video image. It is similar to the way pictures were created on the old television cathode ray tubes by scanning one thin horizontal line at a time. Since each image was only equivalent to one scan line on the television set, many hundred scans had to be taken to create a single frame.
Because the direct recording of light is impossible at that speed, the camera takes millions of repeated scans to recreate each image. Therefore, the technique is only suitable for capturing an event that can be recreated exactly the same way multiple times.
Practical and Important Uses for Femto-Photography
While we will not be seeing this technology used in Atlanta corporate videos for some time, it has some very important applications that can improve all of our lives, and very possibly save them. The team’s leader, Ramesh Raskar, Associate Professor of Media Arts and Sciences at the MIT Media Lab and head of the Lab’s Camera Culture research group, told the audience at the 2012 TEDGlobal Conference that femto-photography could be used in commercial film making one day. “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?”
Dr. Raskar told the conference audience about some more critical future applications for the technology. Because it allows the viewer to “see” around corners beyond the line of sight by using the properties of the photons when they bounce off surfaces and objects, it will someday be used to see inside the body without X-rays.
The ability to see around corners can provide great advances in traffic safety because “we could create cars that avoid collisions with what’s around the bend.” It can also be used in search and rescue efforts and by the military because it would allow rescuers to look for survivors in hazardous conditions by looking at light reflected through open windows.
Femto-photography will lead to important advances in medical imaging by allowing doctors to see deep inside the body with instruments like endoscopes in a way that is not currently possible. Professor Raskar wants scientists to recognize femto-photography “as really a new imaging modality to solve the next generation of health imaging problems.”
“This is how nature paints a photo, one femto frame at a time, but of course our eye sees an integral composite,” Raskar explained. Femto-photography will truly change the way we see the world around us.