Editors' Note: An updated article entitled Why Ultra HD 4K TVs are still stupid was published on January 28, 2013.
The latest TV technology buzzword is "4K." This magical alphanumeric represents a quadrupling of the now-standard 1080p resolution found on Blu-ray and most HDTVs.
Have no doubt, manufacturers are going to start pushing 4K (some already are).
The thing is, though, you don't need 4K, because in the home, 4K is stupid.
Check out Ty Pendlebury's 4K primer for more details about what 4K actually is, because I'm going to spend the bulk of this article describing why you don't need it.
As this is going to be a pretty numbers-heavy piece, let me cover the basic terminology up front. Blu-ray discs, and nearly all modern televisions, are 1080p. This means they have a resolution of 1,920x1,080 pixels. Get up close to your TV when it's on, you'll see the pixels. They're tiny blocks of red, green, and blue (and yellow, if you have certain Sharp LCDs). The image at the top is a closeup of some pixels.
For this entire article, remember we're not talking about content, we're talking about the TV. You can definitely see the difference between content of different resolutions, but that isn't what we're talking about here. We're talking about the HDTV hardware itself.
HD was developed out of necessity given the larger TV screen sizes on the horizon at the time (Ooh, 42 inches!). Standard definition, 480i (roughly 640x480 pixels), looks right terrible when shown on a screen larger than 28 inches diagonal.
The 4K standard is roughly 4,096x2,160 pixels. I say roughly as there isn't a decided standard. So if a company says 3,840x2,160 pixels, that's basically 4K, too (it's more accurately called QFHD, or Quad Full HD). You see, 4K is a cinema standard, and given all the variations in screen widths because of different aspect ratios, it's hard to give one specific number. Suffice it to say, 4K is about double the horizontal and vertical resolution of what you have at home right now.
With the huge screens of most modern movie theaters, and the move toward digital projection, 4K makes a lot of sense. The prevalent 2K (2,048x1,080 pixels) digital cinema projectors are only slightly higher resolution than 1080p. I've seen a lot of these, and I can often see the pixel structure from most of the seats. You definitely don't with 4K, which is why it's a brilliant idea for movie theaters.
But 4K in the home is stupid. Here's why.
Brace yourself for some math
The human eye, for all its amazingness, has a finite resolution. This is why you can read your computer screen from where you're sitting, but not if you're on the other side of the room. Everyone is different, but the average person with 20/20 vision can resolve 1 arcminute. One arcminute is 1/60th a degree. If you assume your field of vision is 180 degrees (it's not, but go with me here), and you take 1 degree of that, you're able to resolve a 1/60th sliver of that degree. Close up this means you can see hairs on your arm, wrinkles on your thumb, and so on. At distance, these fine details disappear. If a friend waves at you from across a field, you can probably see the person's thumbs, but not any wrinkles or hair. Far enough away, you probably won't even be able to see thumbs, unless those are some really, really big thumbs.
One arcminute of resolution is a best-case scenario. On a black on white vision chart, this holds true. Reduce the contrast of the object with the background, add color, and many other factors limit your ability to resolve resolution.
Your over-resolutioned TV
Let's bring this back to TVs.
Depending on technology, a 1080p 50-inch flat panel TV's pixels are approximately 0.023 inch wide. This is presuming they're square (many aren't) and that there's no intra-pixel distance (there is). The plasma I photographed for the lead image above measured 3 pixels per 1/16 inch, which is 0.021 inch per pixel. So we're in the ballpark.
Most people sit about 10 feet from their television. At 10 feet (120 inches), your eye can resolve an object 0.035 inch wide, if like I said above, there's enough difference between it and the background (or its adjacent pixel, in this case). The memories of the Westwood school system that told me I was bad at math compels me to show my work, so feel free to check my math:
2 x pi x 120": 753.98" (circumference of a circle, with you at the center)
753.98 / 360: 2.0944" (360 degrees in a circle)
2.0944 / 60: 0.0349" (60 minutes in a degree)
This math, or just looking at your TV, tells you that you can't see individual pixels. What's interesting is that a 720p, 50-inch TV has pixels roughly 0.034 inch wide. As in, at a distance of 10 feet, even 720p TVs have pixels too small for your eye to see.
That's right, at 10 feet, your eye can't resolve the difference between otherwise identical 1080p and 720p televisions. Extrapolating this out, you'd have to get a TV at least 77 inches diagonal before you'd start having a pixel visibility problem with 1080p.
Or, you can move closer. Beyond being a math exercise, let's be realistic. No one's going to sit 6 feet from a big TV. I'd doubt 7 feet, either. So if we say 8 feet (96 inches), or 0.028 inch on the resolution side, this means you'd need a TV that's bigger than 60 inches to really benefit from 1080p.
Is there a size/distance where you can see the difference in detail, below the raw pixel-size numbers? Possibly; it depends a lot on the content, the display, and the person. Remember, we're not talking about just being able to see something, we're talking about being able to resolve it. You might be able to see a single pixel-width black line on a white screen from great distance, but two black lines separated by a single white line will appear as a single black line. That's detail, and if you're too far away to see it (or the screen isn't big enough), then it's being wasted.
On the other hand, "seeing pixels" also means seeing the pixel structure around objects, square blocks for curves, that sort of thing. So there is such a thing as too close/too big, but it's much farther/bigger than most people realize.
The real world tends to get even more vague, which we'll get to in a moment.
4K 4 U, K?
So if your eye can't tell the difference between 720p and 1080p on nearly all modern televisions, what's the need for 4K?
Excellent question. There isn't one. Not as far as TVs go, anyway. You'd need a 2,160p TV over 154 inches diagonal before you'd be able to see the pixels. On a 4K 50-inch TV, the pixels would be roughly 0.011 inch wide.
Where's the crossover where 1080p and 4K become noticeable? It's not exact because of all the above mentioned variables, but suffice it to say at 10 feet, it's somewhere well above 77 inches.
Let's put this in the real world. I sit 9 feet away from a 102-inch screen. At that distance, I can't see the pixel structure of a 1080p projector. If I lean forward a bit, so my eyes are 7 to 8 feet from the screen, I can see pixels on bright images. If I zoom the projector out to fill all 127.75 inches of my 2.35:1 screen, I can sometimes see pixels depending on the projector.
At this extreme size, and seated far closer than most people would feel comfortable, I would probably be able to see a difference with 4K.
When I reviewed JVC's DLA-X90R, I sure didn't see an increase in resolution. Admittedly, this is far from conclusive, as there's no native 4K content readily available (and the JVC can't accept it even if there was). If I sat about 5 feet from the screen, I could just make out the pixels. As more 4K displays come available, I'll see if I can find that sweet spot of viewing distance.
So that's the advantage of 4K: you can sit way closer to your television (which no one will), or you can get a way bigger television (also unlikely).
When you increase the resolution so significantly (and again, this is all assuming native 4K content, which hasn't been discussed), factors like the contrast ratio, the brightness, and in cases of projectors, the lens and screen material, all become significantly bigger issues.
A few years ago I did a TV face-off with trained TV reviewers and untrained participants with Pioneer's Kuro plasma (768p) against several 1080p LCDs and plasmas. Not one person noticed the Kuro wasn't 1080p. In fact, most lauded it for its detail. Why? Its contrast ratio was so much better than on the other TVs that it appeared to have better resolution. The difference between light and dark is resolution. If that difference is more pronounced, as it is on high-contrast ratio displays, they will have more apparent resolution.
Passive 3D (aka: one more thing)
OK, there's one other way that 4K is actually a great idea: passive 3D. Current passive 3D displays (from LG, Toshiba, and Vizio) are half resolution when viewing 3D. Each eye is getting 1,920x540 pixels. They claim your brain combines these into one "full HD" image, but from where I usually sit, I can see lines in the image, so I cry bollocks.
With 4K, though, passive 3D creates a 3,840x1,080-pixel image per eye, which is more than enough so that you don't see any lines. (Check out Active 3D vs. passive 3D: What's better? for more info on all this.)
Glasses-less (autostereoscopic) 3D displays have the same basic problem, with certain pixels reserved for certain eyeballs. Here, 4K and higher is also a good idea; one could say it's even a requirement.
The 4K standard is already here in the home projector space, more or less. Sony makes a $25k projector that's native 4K, while JVC has several models with the "e-Shift" pixel upconverter that puts 3,840x2,160 pixels on screen even though the LCOS chips are 1,920x1,080 pixels. A case can be made for 4K with larger screens at home. At the moment, though, light output limits screen size far more than resolution. For home projectors, let's just shrug and ask, "OK, why not?"
But with televisions, 4K is stupid. Stupid, stupid, stupid. For every one of you thinking you'll rearrange your living room to sit closer to the screen, I'm positive there are thousands of others who wouldn't (or wouldn't be allowed to).
Sure screen sizes are going up, but how many of you are really going to put an 85-inch screen in your home, and sit close enough to it for 4K to matter?
Don't believe me? Get a chair, and sit close enough to your TV so you can just see the pixel structure. Now watch an entire TV show like that. Now convince your family to do the same.
There's this feeling of inevitability with 4K, like because we can do it, we will do it. I just wanted to point out early that regardless of what the marketing and hype will say, you don't need 4K.
So if someday there's a choice between a 4K 80-inch OLED and a 1080p 80-inch OLED, sure, pick the 4K. Move a little closer to it and presto. But inevitably there will be even smaller 4K displays, and unless you're sitting on top of them, there's no point.
Got a question for Geoff? First, check out all the other articles he's written on topics like HDMI cables, LED LCD vs. plasma, Active vs Passive 3D, and more. Still have a question? Send him an e-mail! He won't tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter: @TechWriterGeoff.