Now you see it… Metameric colours as they look through special filters (top, middle) and unfiltered (bottom) Mikhail Kats and Brad Gundlach

It’s sometimes practically impossible to tell similar colours apart. Even side by side, they look the same. A special pair of spectacles gives us new power to see more distinct colours, and could one day help to spot counterfeit banknotes or counteract camouflage.

The glasses, devised by a team at the University of Wisconsin-Madison, basically enhance the user’s colour vision, allowing them to see metamers – colours that look the same but give off different wavelengths of light – as recognisably distinct hues.

Human colour vision relies on three types of cone cells that react to short (blue), medium (green) and long (red) wavelengths. While brushing up on his knowledge of the eye before teaching a photonics class, physicist Mikhail Kats had a brainwave. Could the eye be tricked into effectively having another type of cone cell?


In theory, this could take our vision from being trichromatic, which uses three colour channels, to tetrachromatic. Some animals see in four (or more) channels. Goldfish, for example, have cells for red, blue, green and ultraviolet light. Some researchers suggest that a very small number of humans may be tetrachromats too.

Read more: Human eye proteins detect red beyond red

To make their glasses, Kats and his colleagues designed two colour filters, one for each eye that strip out specific parts of the blue light spectrum. With each eye receiving slightly different spectral information about blue things, the team hypothesised that any subtle differences in colour would be more pronounced. And they were right.

They tested the effect by displaying blocks of colour that people perceived as metamers on a computer and smartphone screen. To the naked eye, they looked identical, but with the glasses they were easily told apart.

“They look exactly the same and you look through the spectacles and, holy crap, they’re two different things,” says Kats.

The team used two filters because although one filter would reveal differences in certain metamers, it could also make other colours that normally look different appear the same. The two filters counteract this effect.

“It’s a really fun idea,” says Jay Neitz, a colour vision researcher at the University of Washington in Seattle. “There’s no doubt when you do this glasses thing, you would be able to discriminate metamers.”

Neitz has experimented with colour filters in the past, but found that sending different information to each eye can be uncomfortable. Kats’s team made their filters only subtly different, which Kats says improves their metamer-distinguishing ability and makes them no more irritating than sunglasses.

At the moment, the filters only distinguish metamers at the blue end of the visible spectrum. Kats is hoping to target green wavelengths next. Once extended to differentiate between more hues, Kats says the filters could be developed into tools for tasks such as detecting counterfeit currency, seeing changes on the surface of fruit and vegetables that are about to spoil, or picking out camouflaged objects.

“I really want to put these on and go walk around a forest or a park,” he says.

Reference: arxiv.org/abs/1703.04392