EDITORS CHOICE 19.04.17

Letter from America: Turning HDR into a “High Demand Requirement”

HDR 4K logo from side

Any reader of this space has heard it before: it was the initial allure of increased pixel resolution that initially brought 4K/HDR displays to prominence - where they have since taken over all flat-panel display categories over 40-in diagonal (other than at the very lowest price bands). However, what will keep customers from thinking that, as some pundits have said “4K is just another marketing ploy to get people to buy more sets” is a trio of three things. As also repeated here before, it is not just “more pixels”. It is, and must be “better pixels and faster pixels”, as well.

Explaining “more pixels” is easy; it’s a simple matter of comparing 1920x1080 resolution to 3840x2016. That equates to a picture with almost four times as many pixels. That said, it is also often stated that unless the viewer sits very close to the screen, the difference cannot be perceived. What, then, will provide the customer satisfaction that is needed to keep the 4K bandwagon rolling? In our humble opinion while “faster pixels”, more correctly known as high frame rate (HFR), certainly provides a viewable improvement, there isn’t sufficient content for it at this time to make it important. We’ll get back to HFR as the year progresses.

Having put both “more” and “faster” pixels aside for now, that leaves us with High Dynamic Range, or HDR, as the top-level viewpoint for “better pixels”. As my column title this month indicates, HDR has also become a popular differentiation point and sales driver – it is an installer’s job to turn HDR into being a “High Demand Requirement”. Although HDR has been around for a while it often comes off as a mystery to many outside the tech-world. For that reason, it is important to have some background notes for your own presentations and client/prospects. There is more than a keg full of misconceptions, acronyms, abbreviations and standard names and numbers and you should have at least passing familiarity with all of them.

"Promotion by manufacturers where they tout the light output of their displays will lead you in the wrong direction. It is NOT about how bright the image can get. Rather it is about the range of different between the darkest and brightest viewable parts of the image." 

HDR is NOT about brighter images. It’s about contrast.

Promotion by manufacturers where they tout the light output of their displays will lead you in the wrong direction. It is NOT about how bright the image can get. Rather it is about the range of different between the darkest and brightest viewable parts of the image. That is contrast not brightness.

One of the best ways to describe the benefit of increasing that “dynamic rage” and making it “high” is to ask the client to imagine a shot of football pitch on a sunny day. Part of it is quite bright while part of it is in shadow from the stadium stands. HDR makes it possible to have the camera pan from the bright side, where the clouds must stand out in the sky, to the darker side where one needs to see the players without having them disappear into the shadows.

THAT is what HDR is all about.

HDR and WCG are related, but about different things. So are colour space and colour volume.

Conversations about HDR often get around to the mention of the “colour space”. That is a two- or three-dimensional view of which colours. You’ve seen the “triangle inside a color triangle” diagrams that are the CEI 1931 color space representation. Within them you’ll also see one or more triangles labeled “709”, “P3”, 2020 and perhaps others. What this is all showing is a representation of which colors a system can reproduce. That is the colour space; the more colours, the wider the colour gamut. The older “NTSC” and “709” spaces are, well, old. The larger DCI-P3 and Rec.2020 spaces are larger. Or, if you will, wider. Hence the grouping under the name Wide Colour Gamut, or “WCG”.

Over the course of the year you will likely hear more about colour volume. That is a more three-dimensional representation of how much of a given color the system and display can show. Best example? Picture a Coke can or a London Transport bus. Or, where I’m from, think of those bright yellows of NYC taxi cabs and a traditional school bus. Is the set able to accurately show the object’s colour? That’s color space. Is that color properly saturated to the correct extent? That is colour volume.

HDR does not specifically require a given colour space or volume, but it does make you aware of the latter. After all, as the viewer is able to see a greater range between dark and bright it certainly helps to see as much proper colour within that range.

HDR has component parts that all into the different standards

Hang on, this is going to get geeky. An OETF is the “Opto-Electrical Transfer Function”. That is a way to mathematically describe how a camera converts light (or light reflected off a surface) into a digital, or if you will, “electrical” form. More important to us is its inverse, the EOTF, or Electro-Optical Transfer Function, which describes for the electrical/digital representation is turned back into light to reproduce the image on a display.

Various companies and global standards bodies have studied both and the one you need to know about is SMPTE ST-2084. Originally developed by Dolby Labs, but now adopted as a royalty-free standard, it defines the “Perceptual Quantizer”, or “PQ”. And is the core of what you will hear referred to as “HDR-10”. It is based on 10-bit color and does the task of delivering HDR. Part of the HDR-10 package is ST-2086. That defines static metadata that describes the displayed image once for the entire picture content stream.

Dolby Vision goes one step further. It uses 12-bit video and has dynamic metadata. That is critical since it allows the system to adjust the HDR parameters on a scene-by-scene basis. As good as HDR-10 is, many observers say that Dolby Vision is even better.
diagrams showing HDR Dolby Vision Range colour and contrast

Note, however, that while virtually all sets with Dolby Vision are compatible with HDR-10, there are many more sets with HDR-10 only. And, to date, there is only one streaming device, the Chromecast Ultra, that is able to deal with both formats. All other 4K/HDR-capable streaming devices are HDR-10 only. Similarly, while all UltraHD Blu ray players handle HDR-10, Dolby Vision is coming to only some of the players now as a software update.

Why, one might ask, if Dolby Vision is often taken as being better, why don’t all the HDR sets have it? Well, HDR-10 is free and Dolby Vision has a royalty attached to it. Add in the usual CE industry politics and you can figure it out.

But WAIT, there’s more

Along with HDR-10 and Dolby Vision there is also Advanced HDR by Technicolor. Born from the merger of separate standards originally proposed by Technicolor and Philips, it provides the benefits of HDR to compatible sets while simplifying the ability of standard dynamic range (SDR) sets to successfully show the image to the best degree possible. It was a late starter, but it is gaining some traction.

You’ll also see much mention of HLG, or Hybrid Log Gamma. Developed by the BBC and Japan’s NHK, it is another spin on providing more HDR-SDR compatibility, particularly for live broadcasts. It, too, is gaining some traction amongst display manufacturers and the streaming presentation of the latest 4K version of BBC’s Planet Earth series uses it.

Samsung HLG TV comparison with conventionalHere’s the latest standard: HDR-10 Plus. Since static HDR metadata is a weakness of HDR-10, the folks at Samsung have replaces ST-2086 with SMPTE ST-2094 to provide dynamic metadata and compete more fully against Dolby Vision without charging a royalty. It is already in 2017 Samsung sets with HDR, and look for more display brands, content providers and streaming devices to add it going forward.

OK, here’s one more before we wrap this up. By now you’ve likely seen mention of the ITU Rec.2020 standard for color space. Look again, as it is now being updated to Rec. 2100. No, Rec 2100 isn’t just more than “80 points” better than Rec. 2100. What it does is roll the extended WCG colour space, both static and dynamic metadata along with both ST-2084/PQ and HLG into one unified standard. At the end of the day this roll-up will form the core of the DVB standard that will bring the full package of “more, better and faster pixels” to the UK, EMEA and other regions currently operating with DVB.

Here’s the bottom line: don’t worry, it won’t be that bad!

This is one of those areas where in order to compete in the market and be able to credibly answer consumer inquiries you have to be prepared. Remember, HDR and all of its component parts are, and will continue to be not just High Dynamic Range, but a “High Demand Requirement”.

Having made this all sound complicated, we will end by hopefully setting your mind at ease by making it a bit simpler. If you stop and consider all the various audio formats from Dolby, DTS and others you should be able to explain the differences between them, particularly when it comes to the new object-based, immersive formats. However, that is rarely needed.

Why is that? Think about it: while people know that there is more than one standard they also know that in most cases products such as AVRs and surround processors can deal with both types. Often, the user doesn’t even know what format is being played because the AVR takes care of it all for them.

As time moves forward you may expect to see more products do the same for video that they do for audio. Regardless of input format you’ll see displays, streaming devices and content players either have all the formats or at least be able to deal with the various types of HDR. It is true that HDR-10 seems to be turning into common base line and Dolby Vision in many, but not all sets and devices due to cost and political considerations. However, the likelihood of a poor image or blank screen is quite remote.

Where does that leave you? Know what HDR is and does. Understand the different technologies behind it and the formats used to deliver. Then, pause and take a very deep breath. At the end of the day the bottom line is that HDR, or “Better Pixels”, will be a “High Demand Requirement” that will drive your business to heights that are hopefully great as the display image quality.