Why 4K On The Desktop is a Big Deal

This week, a bunch of hardware manufacturers announced 4K monitors (http://www.engadget.com/2014/01/06/asus-28-inch-4k-display/) for about $800. These monitors, which actually aren’t quite 4K (more like 3.8K), cram 3840x2160 pixels into a 28-inch screen. For those of you doing the math, that’s exactly 4x as many pixels as in a traditional HD display, or 2.25x as many as many as the current state-of-the art display, the 27-inch (2560x1440) monitor. 

Computer monitors have had a pretty interesting evolution (or lack thereof) over the years. For a long time, monitors were pretty low-resolution - you were lucky to get 1024x768 in the mid-90s (and for that, you had to spring for a state-of-the-art 17-incher). Then 20-inch CRTs came out in the late 90s, and got us up to 1600x1200. But since then, things have remained relatively stagnant - as monitors transitioned from CRT to LCD, maximum resolutions stayed put, and the only evolution they’ve had is to match the widescreen (16:9) aspect ratio of HDTVs (great if you use your computer for watching movies). Your 2014 23" HD display has a resolution of 1920x1080, which actually gives you fewer vertical pixels than your 20" monitor had 10 years ago. Many professionals use 27” or 30” monitors with more pixels, but the information density is the same. Most desktop displays currently max out at about 100PPI. 4K monitors will finally change this.

So why would you want more pixels on your display? The answer is more complicated than just “you can fit more information onto the screen,” because the human eye can only perceive detail down to a certain level. My 13.3-inch Retina MacBook display contains as many pixels as most 30-inch monitors, but I can’t display it at full-resolution, because the text would be too small (leading to eye strain and eventually blindness). So, the trick is that you can display an image at less than the full resolution, but use the additional pixels to improve the image quality. Apple calls this “HiDPI” - they render the image at twice the indicated resolution, and then display it on a high-resolution display.

Apple’s “retina displays” depend on the principle that your eye can only perceive a certain amount of detail. This is why 1080p screens don’t make much sense on 5” smartphones, except for marketing purposes (a 720p display should be sufficient). When the pixels drop below a certain size, your eye ceases to see them any more, and all that you can perceive is the image they represent. When Apple’s Retina MacBooks first came out, I was skeptical, but then I saw one up close, and decided that they were pretty amazing (I bought the second generation rMBP shortly after it was announced). I don’t get significantly more information on my screen than I did before, but everything definitely looks a lot better.

The threshold for a retina image depends on how far away the device will be (http://isthisretina.com/). For a smartphone, which we hold about a foot from our face, we need about 300 ppi to reach true retina density. For a laptop or tablet, which is perhaps 18 inches away, the required density drops to maybe 220. A desktop monitor is a bit further yet, at about 24-inches, and at that distance, we need maybe 150 ppi to hit retina densities. The upcoming 28-inch 4K displays squeak in under the bar, and will give a significant increase in display sharpness.

While $800 seems like a lot to spend on a monitor, existing 4K monitors cost about $3,000, so that’s a big price drop. 27-inch displays currently cost about $5-700 (excepting the cheap Taiwanese monitors off of eBay), and an Apple Thunderbolt display costs about $1,000. The result is that the new crop of displays will give a pretty big visual upgrade at only a modest price increase, and expect prices to drop further over time. In fact, I wouldn’t be surprised if Apple releases a Thunderbolt display based on this panel, styled the "Retina Thunderbolt Display.”

We only have one remaining issue - many existing computers have trouble displaying a 4K image at full refresh rate (60hz). HDMI and Displayport, the two most common connectors on modern PCs and monitors, max out their bandwidth at about 2560x1600x60hz. If you want to push twice the number of pixels, you have to halve the refresh rate. This is why the one affordable 4K display (

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) is limited to 30hz when you’re using it as a monitor. You have two options for getting around this. One is to put two HDMIs/Displayports on the monitor, and use each for half the image. This doesn’t work too well on most laptops, which only have one video out port. 

The second option is to use a feature of DisplayPort called MST (Multi-Stream Transport) mode. Originally designed to allow Displayport monitors to be daisy chained, it will also enable a single 4K monitor at 60hz. The problem with this is that not all video cards support MST quite yet. The new (trashcan) Mac Pro supposedly includes 4K support via MST mode, and rumor has it that the Retina Macbook Pro supports MST on Windows but not in Mac OS (http://9to5mac.com/2013/12/23/new-retina-macbook-pros-can-drive-4k-displays-at-60hz-when-running-windows-mac-os-needs-new-drivers/). Expect wider support to come in the near future.

So, 4K support is coming soon, and despite all of the nerdy details, I’m guessing that it will actually yield the first major upgrade to desktop displays that we’ve seen in many years. The future is starting to look a lot sharper.