21 Feb 2023
Adopting the animal's ocular structure could help deal with uneven illumination.
Insects and related species have often provided the blueprints for these devices, with examples including the nanostructures based on the eyes of moths that can improve the anti-reflective properties of optical coatings, or the class of 3D camera partly inspired by the multiview vision of flies.
A project at South Korea's Gwangju Institute of Science and Technology (GIST) has now studied a different part of the animal kingdom, designing an artificial vision system inspired by the eyes of cuttlefish.
As published in Science Robotics, the architecture could be particularly valuable as a route to better imaging for future autonomous vehicles and drones, which are often required to operate in less than perfect light or poor visibility conditions.
Cuttlefish are known to be efficient predators, skills partly dependent on having eyes optimized for the available light in waters where the marine molluscs live, and their vision system has evolved to be particularly effective at compensating for vertically uneven illumination conditions.
The animals' eyes are equipped with a W-shaped pupil, a single spherical lens, and a curved retina with a high-density photoreceptor arrangement and polarized light sensitivity. Although only one kind of photoreceptor is present, the architecture allows cuttlefish to distinguish different light sources using polarization of light instead of color.
Guidance for drones and vehicles in poor light
"While researching animal eyes, we discovered that cuttlefish can focus under harsh light conditions, such as in shallow water, thanks to their unique W-shaped pupil and retina structure,” said Young Min Song of GIST. "This inspired us to create an artificial vision system that can also focus in challenging light environments."
The W-shaped pupil turned out to be highly significant, allowing the cuttlefish to balance vertically uneven light fields by favoring light from the horizontal band of the animal's environment. This cuts the amount of direct sunlight that is scattered by the eye's lens, improving image contrast for the dimmer parts of the scene.
The GIST project designed a vision system with its own W-shaped pupil, along with a single ball lens, and a surface-integrated flexible polarizer to replicate the animal's ability to detect polarized light. A cylindrical silicon photodiode array was also employed, with a locally densified pixel arrangement to match the high density of photoreceotor cells in one specialized region of the cuttlefish's retina.
In proof-of-concept trials, the bioinspired architecture proved able to produce images balancing uneven vertical illumination, and reveal patterns of polarization in incoming light, both of which could be valuable in vision systems designed to work in dimly lit outdoor environments or provide vision for autonomous machines.
"With the rise of mobile robotics, including self-driving automobiles and drones, developing artificial vision for high-contrast and high-acuity imaging in vertically uneven illumination conditions has become an important goal," commented the GIST project in its paper. "In such situations, balancing uneven illumination, improving image contrast for facile object detection, and achieving high visual acuity in the main visual fields are key requirements."