University of Cambridge scientists working with researchers from Meta Reality Labs have performed a series of unprecedented experiments, revealing that most people’s eyes can’t tell the difference between ultra-high-resolution 4K and 8K TVs and less expensive, lower pixel-density HDTVs of an average size when viewed at a typical distance.
However, the team also found that the human eye can tell the difference between HD, 4K, and 8K TVs if the viewer is seated close enough or the TV display is exceptionally large. The researchers suggest their findings could guide the development of display technologies, ranging from TVs and smartphones to automotive displays, to determine how much resolution capacity is actually needed for each application.
“Display design should be guided by the limits of human vision, not just by packing in more pixels,” study co-author Maliha Ashraf told The Debrief. “Our study helps define where those limits are, so both screen makers and viewers know when higher resolution stops making a visible difference.”
In a press release detailing the team’s study, Ashraf explained that large engineering efforts to improve the resolution for mobile, Augmented Reality (AR), and Virtual Reality (VR) technologies are still largely based on the widely accepted 20/20 vision standard. Developed in 1862, before display technology existed, the Snellen chart suggests that the human eye cannot resolve detail above approximately 60 pixels per degree.
“If you have more pixels in your display, it’s less efficient, it costs more, and it requires more processing power to drive it,” added study co-author Professor Rafał Mantiuk, also from Cambridge’s Department of Computer Science and Technology. “So, we wanted to know the point at which it makes no sense to further improve the resolution of the display.”
In first-of-their-kind experiments, the Cambridge-led team designed a setup with a sliding display that could be moved toward and away from the viewer. Ashraf told The Debrief the team used a 27” 4K Eizo ColorEdge LCD display instead of designing one specifically for the tests.
“The goal was to use a well-calibrated, stable display, not any specific brand,” the researcher explained.
Ashraf also told The Debrief that the experiments did not evaluate different display technologies, such as OLED or QLEDs, but instead used the single 4K LCD display. The researcher conceded that there can be “small differences” in the arrangement of subpixels across different technologies, but said that the goal of their experiments was to obtain “general estimates” that apply broadly across different kinds of screens.
“Instead, we used a device-independent measure called pixels-per-degree (PPD), which simply describes how many pixels fall within one degree of visual angle on the retina,” Ashraf told The Debrief. “This makes the results transferable to any type of display technology.”
During a series of tests, study volunteers were tasked with detecting specific features on the screen in both color and grayscale. When images were displayed on the screen, the subjects were asked to look for “very fine gradations,” including the fine lines that make up the image. The screen was then moved towards the subjects and also moved further away to measure PPD detectability at different distances. The team performed all tests for both central and peripheral vision.
When evaluating their subjects’ replies, the study authors found several unexpected results. For example, the experiments revealed that the human eye’s resolution was much finer than previously believed. Unlike the 60 PPD used in the Snellen chart 20/20 vision standards, the team found that the average PPD was 94 for greyscale images viewed straight on.
When analyzing the subjects’ PPD perception of color images, the team found that results were similar for red and green images, with an average, robust PPD of 89. However, for yellow and violet images, the PPD dropped to 53. The number was even worse for color images viewed with peripheral vision. Mantiuk said the results were not unexpected, since the brain doesn’t “have the capacity” to sense detail in color very well.
“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,” the researcher explained.
When applying their results to the practical use of HD, 4K, and 8K TVs in the average household, the team found mixed results. For example, in the average UK living room where there are 2.5 meters between the TV and the sofa, the team found that a 44-inch 4K TV or 8K TV “would not provide any additional benefit” over a Quad HD (QHD) TV of lower resolution. However, if a consumer’s TV was large enough, the team did find some potential benefits to K and 8K resolution displays.
“For a very large screen like a 100-inch TV, the pixels are spaced farther apart, so if you sit close enough (around two meters or less in this case) some observers can still see the extra detail an 8K display provides compared to 4K, especially with very fine or textured content,” Ashraf told The Debrief. “Of course, for simpler areas without much detail, like a clear sky or large blocks of colour, the difference would be hardly noticeable.”
As part of the study, the team has unveiled an optimized viewing chart showing the distances and screen sizes at which viewers can and cannot tell the difference between HD, 4K, and 8K TVs.
Viewers can also use a free online calculator that the team created to determine the ideal display size for your sitting area.
“Our results set the north star for display development, with implications for future imaging, rendering, and video coding technologies,” said co-author Dr Alex Chapiro from Meta Reality Labs.
The study “Resolution limit of the eye: how many pixels can we see?” was published in Nature Communications.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.