Can You Really Tell the Difference Between 4K and 8K?

Can You Really Tell the Difference Between 4K and 8K?
Contributor: Daniel Kolitz

Some time ago I came to feel, in a very literal way, the speed of semi-recent technological progress. My roommate — a gamer — had gotten it into his head, possibly via some other gamer, that ‘90s video games look best when played on ‘90s televisions. This led him to secure one on Craigslist, which led in turn to my assisting him in hauling it up the stairs. And it was just, let me tell you, the heaviest fucking thing. I could not believe how heavy that TV was.

In the 25+ years between that TV’s debut and its eventual arrival in my living room, televisions have changed a whole bunch. Now they’re all flat, and not particularly heavy. As you might expect, the screen technology has also improved dramatically. Some pricier models offer 8K UHD resolution, double the previous standard of 4K.

Is the picture on these 8K TVs really twice as good as 4K? At a certain point, are there diminishing returns when it comes to image quality? We reached out to a number of experts to find out.

4K vs 8K: the experts weigh in

Stephen Palmer

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 large your television is and (2) how far away you’re watching it from. The benefits of 8K will be most easily visible on a very large TV viewed from a short distance. They will be virtually invisible on a small TV viewed from far away. The same is true, relatively speaking, of current 4K TVs vs. 2K TVs (1920 × 1080 pixels, aka “1080p”) — they work better with larger TVs viewed at shorter distances.

Pawan Sinha

Professor, Vision and Computational Neuroscience, MIT

Let’s tackle this with some technical detail: Normal visual acuity (what we often refer to as 20/20 vision) corresponds to being able to resolve two dots separated by ‘1 minute of arc.’ What does this mean? One’s thumb, at arm’s length, is about two degrees wide, and a degree has 60 minutes. This means that if you were to draw 120 evenly spaced dots in a line across the width of your thumb, then at arm’s length you would just barely be able to see the individual dots. At any greater viewing distance, or with any more dots, you would be unable to tell the difference between the dotted line and a continuous one. If we translate this calculation to a TV, it turns out that for a screen 60″ wide viewed from five feet away, the limit of our resolution is 4K. At this distance, we would be able to tell the difference between HD and 4K, but any increase beyond 4K (say, to 8K) would not be noticeable. We would need to get right up close to the TV (quite an unnatural thing to do) to tell apart a 4K screen from an 8K one. So, unless one is planning on having a really huge screen, or is planning on watching TV from very close up, 4K is plenty. The step up to 8K (from 4K) will likely be unnoticeable in most living room setups.

Emily Cooper

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

We’ve all experienced situations that push the limits of what our eyes can see. Maybe you’ve struggled to read the tiny text on a food label or strained to recognise the face of a friend in a crowd. While the human visual system is remarkable, it has an array of limits that render some aspects of the world effectively invisible. When it comes to display design, understanding these limits is essential for understanding whether one display will look better than another.

The difference between an 8K television and previous generation displays comes down to an increase in the number of pixels. In modern television displays, individual tiny pixels are arrayed side-by-side in a grid. Each pixel in this grid emits a spot of colour, which together make up the images you see on your television. When you watch your favourite show, you’d like to see these images in high detail without being distracted by also seeing the individual pixels. That is, you want the images to be vivid but the pixels to be invisible.

Will an 8K television deliver improvements on these conditions? It depends on a lot of things, like the display contrast, how big each pixel is, and how far you tend to view from — it even depends on the type of image that you’re looking at and how fast that image is changing. For example, if you view a television from far enough away that each pixel is smaller than your visual system can resolve, the pixels will be invisible whether the display is 4K, 8K, or 100K pixels wide. If you pull out some measuring tape and remember your trigonometry, you can easily calculate the number of pixels per visual degree for your own viewing set up. If you are already above 60 pixels per degree, you’re not likely to see improvement with an 8K television of the same size (for reference, one visual degree is about the width of your thumb held at arm’s length). On the other hand, a display with more pixels can in principle enable you to see more details over a wider field of view if the panel is bigger or if you want to view from close up. This, of course, all assumes the original recording also has 8K resolution or higher.

Increasing pixel count can certainly result in benefits, but the details of how you view, what you view, and where you view from will ultimately determine what is a visible benefit to you.

Martin S. Banks

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

There are recommendations for the resolutions of TV displays, cell phones, etc. These recommendations typically boil down to one thing, which is that the pixel should create a visual angle of “1 minute of arc” or smaller. “Minute of arc” is a technical term, and, despite “minute,” it doesn’t involve time: only space is involved. Think of one minute of arc as a little cone of light coming towards the eye. That’s the pixel on the TV screen, and it comes to a point at your eye. One minute of arc is the angle that 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’re talking about 8,000. A lot of people in my field think the “one minute of arc” recommendation is flawed — that it should be smaller.

Viewing distance also comes into the equation here. Skipping over some maths, it works out that if you have a 2K TV (HD), and it’s 0.91 m tall, you need to sit 9.3 away or closer to appreciate the resolution; if you’re 6.10 m away, there’s no way you can tell the difference between your TV and one that has a somewhat smaller number of pixels. If you have a 0.91 m-tall 4K TV, you’d have to be about 1.37 m away or closer to tell the difference, and nobody sits that close. Go all the way up to 8K, and now you’d have to be two feet from your three-foot-television to appreciate it. You’d have to be a very rare kind of viewer to want to take advantage of that.

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