By Sam Matheny
Ultra HD Forum Board Member, CTO & Executive Vice President at the National Association of Broadcasters.
In Act II, Scene I of Romeo and Juliet, Juliet both asks a question and answers it with a profound statement,
“What’s in a name? That which we call a rose By any other name would smell as sweet.”
At the Ultra HD Forum and in the larger UHD industry, we could turn that phrase a bit and get something like,
“What’s in a name? That which we call Ultra HD By any other name look could look as sweet.”
The use of the “could” instead of “would” in the Ultra HD phrase is because there is room for debate.
You see, there is some confusion around what is in the name, Ultra HD, and what it means. And that confusion is part of a larger ecosystem of terms that many take to mean the same thing, but in reality, are different.
- 2K
- 4K
- 8K
- Quad-HD
- UHD
- Ultra HD (head-scratcher, I know, but UHD is different than Ultra HD)
Our love for great imagery and its production and distribution is what drives our work.
And when one loves something, it can occupy a great deal of time and attention.
And when a group of people loves something, passionate debates occur.
And when having passionate debates, those involved can get ever more nuanced and detailed in their positions and definitions.
And in the heat of such discussions, one could be accused of nitpicking.
But alas, when dealing with Ultra HD and one of its components, high dynamic range (HDR), picking nits kicks off a whole different white-hot debate. So for this blog, let us just focus on clarifying the differences in the terms listed above.
This graphic can help the conversation, but it doesn’t tell the full story as it only deals with spatial resolution. And, because people and marketing gurus frequently mix terms, it gets even worse.
But, using this image, we get the following:
High Definition (HD) consists of either of the two spatial resolutions in the bottom right corner:
- 720p – this is actually 1280 x 720
- 1080p – this is actually 1920 x 1080
It should be noted that the “p” stands for progressive, which is how each frame of video is scanned onto the screen. 1080i is also an HD format where the “i” is for interlace, meaning that alternating sequences of every other line of a frame are how the video is scanned.
Moving progressively out and to the left, we have the following:
2K – 2048 x 1080 – this is a digital cinema format
4K UHD or Quad HD – 3840 x 2160 – also used by Ultra HD Blu-Ray
4K – 4096 x 2160 – this is a digital cinema format
8K UHD – 7680 x 4320 – this is not pictured but is already available in some modern televisions
Just as HD has two spatial resolutions, we also see that UHD does as well. But, the marketing folks decided to simplify all of this for the consumers, which is why we see television sets marketed simply as 4K or 8K. However, these televisions are not showing the true 4K or 8K formats as those are reserved for digital cinema. 4K televisions use the slightly smaller Quad HD.
If you are still with me, we can now get to the definition of “Ultra HD,” which is different from that of “UHD,” even though the “U” in UHD stands for ultra. And a lot of this depends on whose definition one uses.
If I were to split hairs, I could argue that the UHD acronym can be read in two ways. Focusing on spatial resolution, as do some other organizations, one can read (Ultra-High) Definition, which many would understand to mean “at least 4K”.
Since we are the Ultra HD forum, we will focus on our definition, and we read the acronym more as Ultra (High-Definition).
As defined by the Ultra HD Forum, a Foundational Layer of Ultra HD begins with a resolution of 1920 x 1080p with HDR and includes the 3840 x 2160 resolution with or without HDR.
Other components include:
- HDR – high dynamic range (brighter whites and darker blacks via PQ10, HLG10, HDR10)
- WCG – wide color gamut (larger color palette and more vivid colors)
- Channel-based immersive audio
The Ultra HD Forum also defines “additional layers” that fit over Ultra HD. These include:
- 7680 x 4320 spatial resolution
- NGA – next-generation audio (immersive audio such as Dolby AC4, DTS-UHD, MPEG-H)
- HFR – high frame rate (100 or 120 frames per second instead of 30 or 60, which is common in HD)
- Dual-layer and/or dynamic HDR metadata systems such as Dolby Vision, SL-HDR1, SL-HDR2)
- CAE – content-aware encoding
A lot goes into defining Ultra HD, and even more that goes into producing and distributing it. I encourage you to check out our Ultra HD Guidelines section to learn more about these components and Ultra HD.
