Your eyes have their limits. 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 technological giants boast about new, "revolutionary" screens. First 4K, then 8K – and today, just a decade after the launch of the first available UHD models, you can already buy a television with twice the resolution. But... are our eyes even able to notice this?

Where the Meaning of Pixels Ends

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

New version of the 19th-century eye test

Instead of the classic Snellen chart (the one with decreasing letters at the optician), researchers created their own digital equivalent. Their screen allowed for precise measurement of how much detail the human eye can perceive under various 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 field of view. This is a more realistic measure, as it takes into account how far you are sitting from the screen.

Volunteers looked at sets of patterns in different colours, while scientists checked when they began to discern individual lines. In theory, with a so-called 20/20 vision, a person should distinguish details up to 60 PPD. In practice, we often see more.

Grey wins over colour

It turns out that in the case of images in shades of grey, the human eye can perceive even 94 PPD, which is half more than the classical Snellen chart assumes. For red and green colours, the limit drops to around 89 PPD, and in the case of yellow and purple – even to 53 PPD.

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

“We do not have the ability to distinguish colour details in detail – especially at the edges of the field of vision. Our eyes are quite average, and it is the brain that ‘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 motorised camera slider to achieve various pixel resolutions per degree (PPD). The fixation point is a black cross in the centre of the screen, and for peripheral vision, an LED on a curved mast lights up. On the right: the stimuli used – from the top: patterns in shades of grey, 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 be immensely important for designers of new devices – especially in the age of VR and AR, where every pixel counts double. With the new model, it becomes easier to determine when higher resolution really makes a difference, and when it is 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 persuaded to buy another “hyper-realistic” 8K television, check if your eyes can even notice it.

Source: popsci.com