Your eyes have their limit. How much resolution do we really need?

Researchers at Cambridge measured the limits of human vision by sliding a display with varying resolutions. The results were published in Nature Communications.

Every year, television manufacturers and tech giants boast about new, "revolutionary" screens. First 4K, then 8K – and today, just a decade after the premiere of the first available UHD models, you can already buy a television with twice the resolution. But… can our eyes even notice it?

Where the Meaning of Pixels Ends

This question is not just a matter of marketing or wallet. The production and powering of larger screens consume enormous amounts of energy, and therefore environmental resources. A team of scientists from Cambridge University and Meta Reality Labs decided to investigate whether there is something like a "resolution limit" — a point at which additional pixels become simply... unnecessary.

New version of the 19th-century vision test

Instead of the classic Snellen chart (the one with decreasing letters at the eye doctor), researchers created their own digital equivalent. Their screen allowed for precise measurement of how many details the human eye can catch in different conditions. They did not count the total number of pixels, but rather the so-called pixels per degree (PPD) – that is, how many pixels fit into one degree of the visual field. This is a more realistic measure because it takes into account how far you sit from the screen.

Volunteers looked at sets of patterns in various colors, and scientists checked when they began to notice individual lines. In theory, with so-called 20/20 vision, a person should be able to distinguish details up to 60 PPD. In practice – we often see more.

Gray wins over color

It turns out that in the case of images in shades of gray, the human eye can detect even 94 PPD, which is about half more than what the classic Snellen chart assumes. For the colors red and green, the threshold drops to about 89 PPD, and in the case of yellow and purple – even to 53 PPD.

Why? Because our brain is not an ideal color decoder.

"We do not have the ability to distinguish color details in detail – especially at the edges of the visual field. Our eyes are quite average, and the brain ‘fills in’ what it considers to be the truth" – explains Dr. Rafał Mantiuk from the University of Cambridge.

On the left: an experimental setup with a screen sliding on rails, controlled by a motorized camera slider, to achieve different pixel resolutions per degree (PPD). The fixation point is a black cross in the center of the screen, and for peripheral vision, an LED on a curved mast lights up. On the right: used stimuli – from the top: patterns in shades of gray, red-green and yellow-purple stripes, black text on white and white on black background. Source: Nature Communications

What This Means for the Screens of the Future

Understanding how we truly see can have a huge impact on the designers of new devices – especially in the era of VR and AR, where every pixel counts double. With the new model, it is easier to determine when higher resolution actually makes a difference and when it's just an artificial race of numbers. Interestingly, the team also developed a free online calculator that allows anyone to check if their screen has a sensible pixel density based on distance and device size.

So before you are convinced to buy another “hyper-realistic” 8K television, check if your eyes even have a chance to notice it.

Source: popsci.com