A tiny, 3D-printed “eagle-eye” camera developed at the University of Stuttgart in Germany mimics the vision of some of nature's sharpest predators. The “foveated” imaging system, named after the fovea part of the eye, provides a high central acuity that could support new applications in optical sensors, endoscopy, and surveillance drones.
The Benefits of Foveated Imaging
The retina of the eye features a depression, or fovea, where retinal cones are most concentrated and visual acuity is highest. The fovea of eagles, however, are deep, allowing a greater magnification in the central part of a field of view – an advantageous feature for a predator. With the foveated vision, eagles can still spot peripheral enemies, while also focusing on their prey.
A camera, built by University of Stuttgart researchers, attempts to replicate the “eagle-eye” vision. Such high acuity could support tasks that do not require equal clarity across a field of view. Think of a drone that requires high resolution in the center of its imaging field.
“You want to both see where your drone is, but you also want the details in the center of your viewing field,” said Institute of Technical Optics at Stuttgart researcher Simon Thiele.
Creating the Camera
To achieve the high central acuity imaging, the camera has four printed lenses, each with focal lengths ranging from a narrow, 20-degree field of view to a wider, 70-degree field of view. The overlaying images created the fovea-like high resolution in the middle part of the image – and lower acuity in the boundary region. Multiple apertures allow a zoom-in kind of imaging.
“You don't have a single focal length, and a single field-of-view objective,” said Thiele. “You have a whole range; from wide-angle to telephoto, it's all covered.”
The imaging system's lenses were printed onto a CMOS chip to form the multi-aperture camera. The CMOS sensor is 2x3 mm2, but sensor chips are available in 1x1 mm2. The lenses have diameters of 125 μm and are roughly the same height – about the size of a grain of sand.
The technology, close to 100 times smaller than the eye of an eagle, cannot achieve the same performance of the winged predators that can spot prey from miles away, but the working principle is the same.
“We use a telephoto objective to basically zoom into the scenery we want to observe, and at the same time we also use a wide-angle lens to observe our periphery,” said Thiele.
The camera was evaluated in special test setups at the university. A target object, a printed structure on paper, was illuminated and imaged. After comparing the foveated image to the normal light angle image, the researchers saw more sharpness and acuity in the picture's center compared to a single-lens configuration.
The camera was not tested in outdoor environments, because of the high light collection efficiency required. The device is currently designed for small distances, due to its small size.
Future camera modifications could incorporate an anti-reflective coating. The Stuttgart researchers also want to experiment with larger objectives, to achieve more pixels per lens.
The camera's tiny size is valuable, according to the researchers, who see the system being used in a small micro-drone, which, similar to an insect, could transmit a wide-field overview while offering detailed imaging of a certain region of interest. Similarly, the technology could be used in capsule endoscopy with directed vision or as a movable vision sensor on a robotic arm.
“Building the smallest camera in the world is exciting,” said Thiele. “It's the size kind of a grain of salt. It's extremely lightweight. It's the smallest system that you can imagine.”