2021-06-15

The ambiguity of 4K, UHD and Ultra HD

Some confusion around the terms ‘4K’ and ‘Ultra HD’ has been there since the beginning. Around the time when I began a blog about this phenomenon, at the end of 2012, the Consumer Electronics Association or CEA (now Consumer Technology Association or CTA) announced the name they had settled on for this new TV technology: Ultra HD. Much to the dismay of Sony, which had just introduced its first professional and consumer products using the term ‘4K’.    A strict interpretation of the term ‘4K’ meant the Digital Cinema Initiative format with its 4096×2160 resolution, which differed from the TV resolution used in consumer electronics: 3840×2160. For a long time I’ve tried to maintain this distinction (it’s actually still in the ‘bio’ of my blog) but I’ve stopped doing that a few years ago, and now use them more flexibly.      
Strict interpretationLoose interpretation
4KDCI-4K: 4096×2160Also 3840×2160
Ultra HD3840×2160Also 8K (UHD-2)
Also Enhanced HD (1080p HD + HDR)
UHDBroader than Ultra HDInterchangeable with Ultra HD
HDRHigh Dynamic RangeHDR + WCG + higher color resolution
The term ‘Ultra HD’ in the meantime has also become more ambiguous by taking on multiple meanings. The Ultra HD Forum for instance – an organization that more than any other is in a position to define what Ultra HD means – has made the case that 1080p HD video with HDR should also qualify as Ultra HD. This format, that has recently been dubbed ‘Enhanced HD’ by some others in the industry, is supposed to be an attractive alternative to actual 4K to broadcasters, although hardly any have adopted it so far. So while 4K really deals with resolution (it’s around 4,000 horizontal pixels, more or less), Ultra HD may refer to the increased spatial resolution, to high dynamic range, to high frame rate (HFR), and to next-generation audio (NGA). I believe the discussion in the Forum about what exactly constitutes Ultra HD has not fully settled yet, though 1080p HD SDR SFR video with NGA is generally considered not to be Ultra HD. Also read: The HDTV is officially dead The latest debate that can cause further confusion is the suggestion that UHD and Ultra HD don’t mean exactly the same thing – that Ultra HD covers also Enhanced HD but that UHD is at least ‘4K’. This would reflect the difference in scope between the UHD Alliance (which only deals with video of at least 4K) and the Ultra HD Alliance which also covers Enhanced HD. It’s an interesting idea but I will probably continue to use the two interchangeably for the time being.

Adding to the confusion

And then there’s yet more ambiguity. I have not yet mentioned Wide Color Gamut (WCG) and higher color resolution (10-bit and beyond). These two aspects are regarded by many observers to be part and parcel of HDR but as I have explained in this article they are three distinct things that make a great combination but can occur separately in the field. You could argue (as I have here) that High Frame Rate means different things in cinema, in television and in gaming, but what it means in TV is quite straightforward. I will skip over the distinction between channel-based and object-based audio as there seems to be a general understanding that Next-Gen Audio means the latter. This covers Dolby Atmos, DTS:X and MPEG-H. I’m doing my best to keep things clear in the things I post but feel free to ask me anytime in case of any doubt.
Yoeri Geutskens works as a consultant in media technology with years of experience in consumer electronics and telecommunications. He writes about high-resolution audio and video. You can find his blogs about Ultra HD at @UHD4k and @UltraHDBluray.