Many modern living rooms are now dominated by huge TVs, but researchers say there may not be much point in buying an ultra-high-definition model.
Scientists from the University of Cambridge and Meta, which owns Facebook, found that for the average living room, a 4K or 8K screen offers no noticeable benefit over a similarly sized 2K screen often used in computer monitors and laptops. In other words, there is no perceptible difference in how clear the image appears to our eyes.
“At a certain viewing distance, it doesn't matter how many pixels you add. I guess it's just wasteful because your eye can't detect them,” said Dr Maleeha Ashraf, first author of the study from the University of Cambridge.
Ashraf and his colleagues, writing in the journal Nature Communications, describe how they set out to determine the resolution limit of the human eye, noting that while 20/20 vision implies that the eye can resolve 60 pixels per degree (PPD), most people with normal or corrected vision see better.
“If you design or estimate display resolution based only on 20/20 vision, you are underestimating what people can actually see,” Ashraf said. “That's why we directly measured how many pixels people could actually distinguish.”
The team used a 27-inch 4K monitor mounted on a mobile cage that could be moved towards or away from the viewer. At each distance, 18 participants with normal or corrected-to-normal vision were randomly shown two types of images. One type of image had one-pixel wide vertical lines of black and white, red and green, or yellow and purple, while the other was a simple gray block. Participants were then asked to indicate which of the two images contained lines.
“When the lines become too thin or the screen resolution is too high, the pattern is no different from a simple gray image,” Ashraf said. “We measured the point at which people could barely tell them apart. That's what we call the resolution limit.”
Researchers have discovered that the human eye can discern more detail than is commonly believed. The average was 94 PPD for grayscale images viewed directly, and 89 PPD for red and green patterns. For yellow and purple models it was lower – 53 PPD.
In another experiment, 12 participants were presented with white text on a black background and vice versa, again at different distances, and were asked to indicate when the text looked as clear as a clear reference version.
“The resolution at which people stopped noticing differences in the text was consistent with what we saw in the line patterns,” Ashraf said.
The researchers published a chart showing various screen sizes and viewing distances, as well as the closest standard resolution that reaches or slightly exceeds the visual limit for most people.
“In other words, if your rig falls into one of these boxes, you won't get any apparent benefit from going higher,” Ashraf said.
The team also created free online calculator It allows users to enter viewing distance as well as screen size and resolution, with the results indicating whether the setting is above or below the resolution limit of the human eye. As a result, users can find out whether a higher resolution screen with more pixels will affect what they see.
“If someone already has a 44-inch 4K TV and is watching it from about 2.5 meters away, that's already more detail than the eye can see,” Ashraf said. “Upgrading to the same size 8K version won't look any better.”
