Researchers study the eye’s resolution limit. Turns out we don’t need full HD

Amazon 4K Ultra-high definition TV. (Shutterstock/Piotr Adamowicz)

As anyone who’s been to the optometrist knows, the human eye has its limits. But a recently published study in Nature Communications has found the limit when it comes to resolution.

Researchers at the University of Cambridge and Meta Reality Labs found that the human eye is limited as to the resolution details it can see, regardless of if it’s a TV screen with full high definition (HD), 4K or 8K.

Since manufacturers are constantly promoting bigger and better televisions with higher definition, researchers wanted to know if there’s a point where adding more pixels doesn’t change anything, because the human eye can’t resolve the details.

“We’re looking at pixels all the time on phones, screens and laptops,” Dr. Maliha Ashraf, one of the study’s authors, told CTVNews.ca. “We wanted to find out is there an upper limit where adding more pixels doesn’t really benefit anyone.”

Ultimately, what they discovered was the more pixels you have on your display, the less efficient it is, as well as being more costly and requiring more processing power.

The study involved 18 participants being shown patterns on a sliding display with fine gradations, in shades of grey and colour. They were asked if they were able to see the lines in the image. The screen was moved closer and further away from them to measure pixels per degree (PPD), a measurement of how many individual pixels can fit into a one-degree slice in a person’s field of vision.

The study found that when the pixel resolution exceeds the visual limit of the observer, they cannot reliably distinguish between the plain grey image and fine lines patterns.

So instead of answering the question “how high is this screen’s resolution?”, measuring PPD tries to resolve “how detailed does the screen look from where I’m sitting?”

“The lines merge together and appear as a grey block,” said Ashraf.

The point at which the observers couldn’t distinguish between the two images meant they’d reached their resolution limit. Adding more details or pixels beyond that wouldn’t make the image look any sharper, because the eye simply can’t see it.

Based on the Snellen chart, which established the 20/20 vision standard, the human eye can resolve details at 60 pixels per degree. But based on their measurements, the number researchers landed on was 94 pixels per degree for greyscale images viewed straight on. The number went down to 89 PPD for red and green patterns, and 53 PPD for yellow and violet.

Study co-author and Cambridge professor Rafał Mantiuk says our brains don’t have a strong capacity to sense details in colour, which is why researchers saw a big drop-off for colour images, particularly when viewed in peripheral vision.

“Our eyes are essentially sensors that aren’t all that great, but our brain processes that data into what it thinks we should be seeing,” Mantiuk said in a press release.

The researchers came up with a free online calculator for users to enter the size of their room, along with the dimensions and resolution of their TV, to help figure out the most compatible screen for their home.