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What is 2K and 4K Video?
As we move beyond 1080p, consumers and the online video world are being enticed by 2K, 4K, and 4K Ultra HD (UHD). Here's a look at what those all mean, as well as what the future might hold.

At this point you may be scratching your head, wondering why consumer electronics manufacturers don't call the Ultra HD models 2K UHD. While one could argue that the term 2K would be too confusing, it's more than likely that someone in the CE world thought consumers would take the 2K term as only being twice the resolution, while they might see 4K as "4X" or four times the resolution.

And that's actually the case: 4K resolution (with a 2x increase on both the horizontal and vertical resolutions) is actually 4 times the resolution of 1080p. The increase from 2,073,600 pixels to 8,294,400 pixels is exactly four times the resolution.

Yet the difference in quality between DCI 4K and 4K UHD also grows, from 8.84 Mpx for DCI to 8.29 Mpx for consumer displays. Where 2K to 1080p was only  difference of 3.43 per cent, the difference between DCI 4K and 4K UHD doubles to 6.67 per cent.

So why don't we have premium content yet for 4K UHD monitors? The answer lies in the film industry's penchant for shooting content at 3-4 times the resolution at which it will be displayed. Currently the majority of digital cinema cameras shoot at between 4K to 5K, and it is only film resolutions of 70mm that come close to achieving 8K digital resolutions.

As film production moves away from celluloid, most content shot on RED and other digital cinema cameras is trapped in that 5K range, meaning that only films shot on, well, film have the "pixel" density to be scanned by 8K scanners. The upside is that, just like 4K UHD isn't really 4K, the 8K scanners required for 4K UHD production needn't really be 8K: 7680 x 4320 pixels, or 33.18 Mpx, will suffice.

Streaming 4K

Bringing it back around to 4K resolutions for streaming, examples are few and far between. YouTube, for instance, uses a "4K" resolution with a 4:3 aspect ratio of 4096 x 3072 pixels for uploading. At 12.58 Mpx the YouTube 4K is almost one-third higher overall resolution than 4K UHD, but YouTube doesn't actually allow streaming of this 4K content.

Instead, YouTube limits browser playback to 2048 x 1536 pixels, or about fifty percent greater than 1080p HDTVs, but well within the reach of higher-end desktop computer monitors. Using the YouTube downloader, though, the original content can be downloaded for desktop viewing, assuming you've got a very high-end computer monitor.

Conclusion

As the streaming industry prepares to take on 2K streaming, with its just-slightly-above-1080p resolution, it also needs to consider which of the 4K resolutions it will gravitate towards. Will it be DCI 4K, which can be displayed on high-end computer monitors, or 4K UHD, which uses a 16:9 aspect ratio and can therefore be the focus of a future 4K UHD set-top boxes?

More importantly, what will the bandwidth implications be of a 8.3 Mpx or greater stream be for the average consumer?

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