Cat's Eye Camera Can See Through Camouflage

Did that rock move, or is it a squirrel crossing the road? Tracking objects that look a lot like their surroundings is a big problem for many autonomous vision systems. AI algorithms can solve this camouflage problem, but they take time and computing power. A new camera designed by researchers in South Korea provides a faster solution. The camera takes inspiration from the eyes of a cat, using two modifications that let it distinguish objects from their background, even at night.

In the future ... a variety of intelligent robots will require the development of vision systems that are best suited for their specific visual tasks," says Young Min Song, a professor of electrical engineering and computer science at Gwangju Institute of Science and Technology and one of the camera's designers. Song's recent research has been focused on using the perfectly adapted" eyes of animals to enhance camera hardware, allowing for specialized cameras for different jobs. For example, fish eyes have wider fields of view as a consequence of their curved retinas. Cats may be common and easy to overlook, he says, but their eyes actually offer a lot of inspiration.

This particular camera copied two adaptations from cats' eyes: their vertical pupils and a reflective structure behind their retinas. Combined, these allowed the camera to be 10 percent more accurate at distinguishing camouflaged objects from their backgrounds and 52 percent more efficient at absorbing incoming light.

Using a vertical pupil to narrow focus

While conventional cameras can clearly see the foreground and background of an image, the slitted pupils of a cat focus directly on a target, preventing it from blending in with its surroundings. Kim et al./Science Advances

In conventional camera systems, when there is adequate light, the aperture-the camera's version of a pupil-is small and circular. This structure allows for a large depth of field (the distance between the closest and farthest objects in focus), clearly seeing both the foreground and the background. By contrast, cat eyes narrow to a vertical pupil during the day. This shifts the focus to a target, distinguishing it more clearly from the background.

The researchers 3D printed a vertical slit to use as an aperture for their camera. They tested the vertical slit using seven computer vision algorithms designed to track moving objects. The vertical slit increased contrast between a target object and its background, even if they were visually similar. It beat the conventional camera on five of the seven tests. For the two tests it performed worse than the conventional camera, the accuracies of the two cameras were within 10 percent of each other.

Using a reflector to gather additional light

Cats can see more clearly at night than conventional cameras due to reflectors in their eyes that bring extra light to their retinas.Kim et al./Science Advances

Cat eyes have an in-built reflector, called a tapetum lucidum, which sits behind the retina. It reflects light that passes through the retina back at it, so it can process both the incoming light and reflected light, giving felines superior night vision. You can see this biological adaptation yourself by looking at a cat's eyes at night: they will glow.

The researchers created an artificial version of this biological structure by placing a silver reflector under each photodiode in the camera. Photodiodes without a reflector generated current when more than 1.39 watts per square meter of light fell on them, while photodiodes with a reflector activated with 0.007 W/m² of light. That means the photodiode could generate an image with about 1/200th the light.

Each photodiode was placed above a reflector and joined by metal electrodes to create a curved image sensor.Kim et al./Science Advances

To decrease visual aberrations (imperfections in the way the lens of the camera focuses light), Song and his team opted to create a curved image sensor, like the back of the human eye. In such a setup, a standard image sensor chip won't work, because it's rigid and flat. Instead it often relies on many individual photodiodes arranged on a curved substrate. A common problem with such curved sensors is that they require ultrathin silicon photodiodes, which inherently absorb less light than a standard imager's pixels. But reflectors behind each photodiode in the artificial cat's eye compensated for this, enabling the researchers to create a curved imager without sacrificing light absorption.

Together, vertical slits and reflectors led to a camera that could see more clearly in the dark and isn't fooled by camouflage. Applying these two characteristics to autonomous vehicles or intelligent robots could naturally improve their ability to see objects more clearly at night and to identify specific targets more accurately," says Song. He foresees this camera being used for self-driving cars or drones in complex urban environments.

Song's lab is continuing to work on using biological solutions to solve artificial vision problems. Currently, they are developing devices that mimic how brains process images, hoping to one day combine them with their biologically-inspired cameras. The goal, says Song, is to mimic the neural systems of nature."

Song and his colleague's work was published this week in the journal Science Advances.