Can you really tell the difference between 4K and 8K?

Illustration: Benjamin Currie/Gizmodo

Some time ago I began to feel, in a very literal way, the speed of semi-recent technological advancement. My roommate—a gamer—had gotten it into his head, possibly through another gamer, that 90s video games look best played on 90s TVs. This prompted him to get his hands on one on Craigslist, which in turn led to me helping him drag him up the stairs. And it was just, let me tell you, the toughest thing. I couldn’t believe how heavy that TV was.

In the more than 25 years between that TV’s debut and its eventual arrival in my living room, TVs have changed a lot. Now they are all flat and not particularly heavy. As you would expect, the screen technology has also improved dramatically. Some more expensive models offer 8K UHD resolution, double the previous standard of 4K. Is the picture on these 8K TVs really twice as good as 4K? Will there be diminishing returns at some point when it comes to image quality? For this week Giz asks, we reached out to some experts to find out.

Professor, Psychology, University of California Berkeley, whose research focuses on visual perception, attention and memory

The obvious answer is that it depends on (1) how big your television is and (2) how far you look at it. The benefits of 8K will be most apparent on a very large TV viewed from a short distance. They will be virtually invisible on a small TV viewed from afar. The same is true, relatively speaking, for today’s 4K TVs versus 2K TVs (1920×1080 pixels, also known as “1080p”) – they work better with larger TVs viewed at shorter distances.

Professor, Vision and Computational Neuroscience, MIT

Let’s tackle this with some technicalities: normal visual acuity (what we often call 20/20 vision) is equivalent to being able to solve two points separated by ‘1 arc minute’. What does this mean? A person’s thumb, at arm’s length, is about two degrees wide and one degree has 60 minutes. This means that if you drew 120 evenly spaced dots in a line the width of your thumb, you would barely be able to see the individual dots at arm’s length. At a greater viewing distance, or with more dots, you wouldn’t be able to tell the difference between the dotted line and a solid line. If we translate this calculation to a TV, it turns out that for a 60″ wide screen viewed from five feet away, the limit of our resolution is 4K. At this distance we could see the difference between HD and 4K, but beyond any increase 4K (e.g. up to 8K) wouldn’t be noticeable We would have to get close to the TV (pretty unnatural thing to do) to distinguish a 4K screen from an 8K screen. screen, or plan to watch TV up close, 4K is enough.The move to 8K (from 4K) will probably be unnoticeable in most living room setups.

“Unless you plan to have a really big screen, or plan to watch TV up close, 4K is enough.”

Assistant Professor, Optometry & Vision Science, University of California, Berkeley

We have all experienced situations that push the boundaries of what our eyes can see. Perhaps you’ve struggled to read the small text on a food label, or you’ve struggled to spot a friend’s face in a crowd. While the human visual system is remarkable, it has a series of limitations that effectively make some aspects of the world invisible. When it comes to display design, understanding these limits is essential to understanding whether one screen looks better than another.

The difference between an 8K TV and previous generation screens comes down to an increase in the number of pixels. In modern television screens, individual small pixels are arranged side by side in a grid. Each pixel in this grid emits a spot of color, which together form the images you see on your television. When you watch your favorite show, you want to see these images in detail without being distracted by seeing the individual pixels as well. That is, you want the images to be vibrant, but the pixels to be invisible.

Will an 8K TV bring improvements under these circumstances? It depends on many things, such as screen contrast, how big each pixel is, and how far you look – it even depends on the type of image you’re looking at and how quickly that image changes. For example, if you watch a television far enough away that each pixel is smaller than your visual system can resolve, the pixels will be invisible, whether the screen is 4K, 8K, or 100K pixels wide. If you pull out a tape measure and remember your trigonometry, you can easily calculate the number of pixels per visual degree for your own viewing setup. If you’re already above 60 pixels per degree, you probably won’t see any improvement with an 8K TV of the same size (for reference, one visual degree is about the width of your thumb at arm’s length). On the other hand, a display with more pixels can basically allow you to see more detail over a wider field of view if the panel is larger or if you want to get a closer look. This, of course, assumes that the original recording also has a resolution of 8K or higher.

Increasing the pixel count can certainly bring benefits, but the details of how you look, what you’re viewing, and where you’re looking from ultimately determine what a visible benefit is to you.

“It depends on a lot of things, like the screen contrast, how big each pixel is and how far you tend to look – it even depends on the type of image you’re looking at and how quickly that image changes.”

Martin S. Banks

Professor, Optometry, Vision Science, Neuroscience, & Psychology, University of California, Berkeley

There are recommendations for the resolutions of TV screens, mobile phones, etc. These recommendations usually boil down to one thing, which is that the pixel should create a visual angle of “1 minute of arc” or less. “Arc minute” is a technical term and despite “minute” it does not involve time: it only involves space. Think of an arcminute as a small cone of light coming to the eye. That’s the pixel on the TV screen, and it comes to a point on your eye. A minute of arc is the angle the cone makes from your eye to the pixel. An HD TV has 2,000 pixels from left to right, a UHD TV has 4,000, and here we are talking about 8,000. Many people in my field think the “one minute arc” recommendation is flawed – that it should be smaller.

Viewing distance also comes into the equation here. Skipping some math, it turns out that if you have a 2K TV (HD) and it’s 3 feet tall, you’ll need to sit 9.3 or closer to appreciate the resolution; if you’re 6 meters away, there’s no way you can tell the difference between your TV and a TV with a slightly smaller number of pixels. If you have a 3 meter high 4K TV, you have to be about 4.5 meters or closer to see the difference, and no one is that close. Go all the way up to 8K, and now you’d have to be five feet from your ten-foot television to appreciate it. You have to be a very rare kind of viewer to want to take advantage of that.

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