With his gray mane, jeans, and dark t-shirt, Diego Gutiérrez Pérez (Zaragoza, 55 years old) could pass for a rock singer, but he is a computer engineer who could also be described as a light master. Many of the advances he has achieved from the laboratory he directs at the University of Zaragoza are based on how our brain perceives light.
Coincidentally, on the day of the interview with this newspaper, he is wearing a t-shirt with that word printed in English -light. It is a promotional garment from a company, he explains while heading to the photographer after a talk where we reviewed the achievements and projects of a career for which he has just received one of the National Computer Science Awards -the Aritmel Award-. It was awarded to him by the BBVA Foundation and the Spanish Computer Science Society for his pioneering research in the field of virtual reality and computational imaging. These works have led him to collaborate with some of the most prestigious universities in the world, with companies like Disney or Adobe, and with NASA.
His love for space is evident as soon as you enter his office, decorated with an iconic photograph of Apollo 11, images of planets taken by NASA probes, and a map of the sky on his birth date given to him by a student. On a table, he has mugs from universities like Stanford or Yale where he has done stays and the awards he has received. "In addition to the one I just received, the one that made me the most excited was the one awarded to me two years ago by the European Society of Graphic Designers for my career," says this professor from the Department of Computer Science and Systems Engineering at the University of Zaragoza.
He arrived here at 18 to study industrial engineering and has stayed: "At that time, almost all of us who studied Sciences ended up doing engineering, and there weren't as many options. I chose industrial engineering almost by inertia. Halfway through the degree, I realized that I didn't like it much, but it was too late to change, so I decided to finish it," he recalls. "Right after, Toy Story and Jurassic Park came out one after the other. I found it incredible that a computer could do that, and I wanted to know how it was done, so I started my doctoral thesis in computer engineering."
The release of those movies was one of the two elements that encouraged him to dedicate himself to this world. The other was his passion for space. "My father brought home the National Geographic magazine, Carl Sagan's Cosmos series was a must-watch, and I was very attracted to space research," he recalls. At that time, he did not imagine that he would end up collaborating with NASA on a project to reconstruct the caves of the Moon.
"I started with computer graphics, which is the process of generating images with a computer. You simulate the interaction of light with materials and how they become visible, in other words, you simulate the transport of light. Virtual reality takes it a step further because it makes it immersive and interactive. And we also work with computational imaging, which is the other side of computer graphics: how can I capture images of the real world in ways that allow access to information that I don't usually have," he explains.
"The most classic example I have worked on is when we managed to photograph light in motion, at a speed of one trillion frames per second. That information is in the world, but with a regular camera, you can't capture it." This innovative technique is called femto-photography and is so fast that it allows capturing and visualizing how light propagates.
They achieved this in 2013 through a collaboration with the Massachusetts Institute of Technology (MIT), where he and his colleague Belén Masiá were conducting a research stay. It was about to be the 50th anniversary of the iconic image that captured the exact moment a bullet pierced an apple. It was taken by MIT engineer and photographer Harold Edgerton, a pioneer in high-speed scientific photography that makes visible what happens too quickly for the human eye to perceive. "We thought about doing something as a tribute, and someone said, 'The fastest thing in the universe is light, we could capture light in motion.' It seemed like a crazy idea, but we managed to design a system that did just that," Gutiérrez recalls.
On his computer, he projects the video of the experiment they did and recorded at MIT: they shoot a very short laser pulse that passes through a Coca-Cola bottle filled with water and a little diluted milk to see how light interacts. "Of all the things we have done, this camera has been the one that has attracted the most attention for many reasons. It's like a temporal microscope. For example, if you put a piece of paper under a microscope, you see all the fibers; it allows you to see things that you can't see at a normal scale. With this camera, we slow down time so much that you can see things happening that normally seem instantaneous," he explains. To understand it, he gives the following example: "When you enter the bathroom and turn on the light, you see your reflection in the mirror. For that to happen, light has to travel from the bulb to your face, to the mirror, and to your eyes, at 300,000 km/second. It happens very quickly but not instantaneously. And with our system, we can literally see how it happens. We put an object in front of the mirror and see how the reflection is formed as the light photons complete that path."
This scientific study was published in 2013 in the journal ACM Transactions on Graphics, and 11 years later, they received the award for the most influential article of the decade in that field: "After that paper, many people started researching this. It is very satisfying because it is what one aspires to in science; you want to open horizons and make things happen," he says. "Belén Masiá, Adrián Jarabo, and I participated in the project. Everything we have achieved has always been as a team because in science, the era of solo advances, like the newtons or the einsteins, is over," he concludes.
"Later, someone at MIT came up with the idea that maybe we could use this system to see through corners." And so, in 2019, they published a work in the journal Nature on a technology that allows acquiring images outside the line of sight, such as scenes hidden behind a corner or invisible to the human eye due to the presence of an obstacle, such as a wall, smoke, or fog.
This system is based on reconstructing hidden geometries, which is achieved by interpreting the information provided by photons that are shot from a light source when they return to the camera. "If a wall covers a doll, the camera cannot see it, but if you shoot many photons with a light source that hit that doll and bounce back, through a simple equation and not-so-simple mathematics, you can reconstruct the hidden scene. That is, by pointing at that wall, we can have information about the photons that have been around the corner and ask them what they have seen. It is a data-based reconstruction, not a simulation of what is hidden," he clarifies.
This technology is still in development, but they already have some possible applications in mind, such as in the field of medical imaging: "Many operations require a camera inside the body to have a line of sight with the area to be operated on. Imagine being able to visualize it without needing that line of sight, without a camera inside you. Another possible use is in car driving. Almost all cars already have a system that brakes if something crosses in front. Our system could anticipate what is happening around the corner and tell you, for example, if a child is crossing or a bike is poorly parked."