The truth about 4K resolution
When you are used to the big numbers in digital still photography, digital video seems positively wimpy. These days, digital cameras with a resolution in the 14 to 18 megapixel range are common. Even my first decent digital camera, a dozen years ago, had a resolution of 3.3 megapixels. But a shiny new home theatre projector or the very latest TV tops out at just under 2.1MP… with a couple of exceptions.
One exception is Sharp, which has a range of TVs (‘Quattron’) which potentially has 2.76MP, but Sharp has arranged it so that it is still a 2.1MP TV, with four subpixels per actual pixel.
The other are some projectors which are just starting to appear. Labelled ‘4K’, they have four or more times as many pixels as a Full HD one.
It’s in the numbers
The current consumer video standards top out at Full HD, in which the picture is presented on a grid of pixels measuring 1,920 across by 1,080 high. Multiply each of those two figures by two and you get something close to 4K.
In general 4K refers to the horizontal resolution. ‘K’ is the computer equivalent of a thousand, or 2 raised to the 10th power: 1,024. So 4K stands for 4,096 pixels across.
Well, much of the time anyway. It can also refer to a horizontal resolution of 3,840 pixels, which of course is precisely double the full HD resolution. In just about all cases, the vertical resolution is 2,160 pixels (double that of full HD).
So, ‘4K’ may refer to either 4,096 by 2,160 or 3,840 by 2,160 pixels.
Either way, that’s a lot of pixels. Figure 1 shows how the relative consumer level resolutions compare to 4K. Full HD and 720p both present in the same aspect ratio as their native resolutions. DVD is always scaled up horizontally to 768 pixels (for 4:3 aspect content) or 1,024 pixels (for anamorphic 16:9).
As you can see, the purple and red boxes are much, much bigger than the others.
Anyone paying attention to consumer video these past few years will have noticed how much picture resolution has improved with the introduction of Bluray. On the raw numbers Blu-ray offers five times as many pixels as DVD.
Well, on the raw numbers, 4K offers four times as many pixels as Blu-ray! But sometimes numbers aren’t the whole story.
What’s the point of higher resolution? If you’re sitting 4m away from a 107cm Full HD display watching a Blu-ray disc, increasing the resolution of both the source and the display will not yield any visible difference.
The point of higher resolution is to allow you to sit closer to the screen, or have a larger screen, than is comfortable with lower resolution material and display.
My words are a bit unwieldy here because I am taking pains to include both the display and the content. Over the years many equipment makers have suggested that their devices can do something which they cannot: somehow turn lower resolution material into higher resolution.
Despite those TV shows where the technician applies some tricky processing algorithm to low resolution surveillance footage in order to reveal the registration number from what was formerly a blob of a number plate, you can do no such thing. No amount of processing can recreate something lost in the source. All that it can do is add made-up stuff.
This means the benefits of 4K – being able to sit closer to a big screen with ultra-clear detail – depend on both the equipment and the content. And for the great bulk of existing content – especially anything made more than 20 years ago – 4K is unlikely to offer anything much. Indeed, as I show on my own web site, while the picture quality on most Blu-ray discs is significantly better than that of the matching DVDs, in many cases the differences are really quite marginal.
And for some it is barely noticeable.
That said, there is a lot of recent content – both animated and live action – which is so sharp that it clearly makes use of every pixel available in Blu-ray, and would presumably benefit even more from a full 4K system. And more and more new content will be the same.
Because, of course, an increasing amount of cinematography is being performed with 4K digital video equipment, and there’s little reason to think it will stop there. One of the innovators in this field, the Red Digital Cinema Camera Company – which introduced the 4K-capable Red One in 2007 is talking about ever higher resolutions in newer models. Other 4K cameras are available from JVC, Sony and Canon.
Regardless of consumer formats, 4K capture is a good idea on the general principle that the highest possible resolution recording is good. Most video these days is subject to a great deal of post production processing, and one good way to keep that invisible to the final audience is to perform it at high resolution.
We are also on the verge of seeing 4K consumer equipment.
When HDMI version 1.4 was released in 2009, it catered for the first time for 4K video (formally: 4,096 by 2,160 pixels at 24 frames per second with up to 36 bit colour).
Already some Onkyo home theatre receivers feature 4K signal handling, and indeed upscaling to 4K.
The JVC DLA-X70R and JVC DLAX90R home theatre projectors offer 4K (of the 3,840 pixel variety) resolution, although with wrinkle that they still use standard HD SXRD panels. They use something the company calls ‘e-Shift’ technology to electronically move the pixels into slightly different positions, thereby creating a 4K image.
These projectors do not accept a 4K signal, though. They internally upscale from normal Full HD. JVC says that the advantage of this system is that it eliminates ‘any visible stair-stepping and pixel gaps’. Fair enough. If you are sitting too close to your full HD screen, those could become a problem, especially the first. But that is not the same as actually providing more detail.
Meanwhile Sony has stepped into the game with a real 4K projector, with the full 4,096 horizontal resolution and support for 4K signals. It presently costs about $25,000, but then I remember the days when the cheapest full HD projector cost $40,000.
The hole in the middle
But there’s a mighty big hole here: there is no practicable way for a regular consumer to get some of that lovely 4K content directly out of Hollywood’s rendering/post-production video computers into a 4K display.
Blu-ray doesn’t do it; it tops out at full HD. There is no industry agreement on a new format to up the resolution. Such a thing would be possible, I suppose. A variation on Blu-ray might do the trick, with four or more layers of data and making use of the latest advances in lossy compression technology.
But there doesn’t seem too much enthusiasm in the industry for this step at the moment, no matter how much we enthusiasts may want it. For the development work to take place and products to be brought to market, at least a moderately large market must be hoped for.
Yet at the moment I am seeing some of the home entertainment arms of movie producers actually cutting back a little on releasing Blu-ray versions of new movies. Sure, the big releases get Bluray discs released alongside the DVDs, but the second tier releases often don’t.
So, the future for higher resolution at the consumer level doesn’t seem that strong for the immediate future.
If you have money to splash on such things, then go for it. At least you can sit a little closer to the screen without jaggies on Full HD material. But for most of us, the best thing to do is purchase the best Full HD display we can manage.