HDR or High Dynamic Range is a term that is used very commonly in today's context- A HDR photo, A HDR display, HDR streaming and gaming and HDR upscaling. So what really is that magical thing called HDR?

Before we understand what High Dynamic Range is, lets first touch on the subject of Dynamic Range. Dynamic Range is the difference between the brightest white colour and the darkest black colour. So a display with a high dynamic range allows for better colours and more contrast.

The way this works is for a display, the peak brightness should be pretty high as is the case with LCD’s which can easily touch 1000 nits of brightness, but they do not get dim enough when displaying blacks, but despite that the high brightness helps it give a higher dynamic range.

While in OLED/ AMOLED panels, the display can reach very low levels of brightness (By low, they actually turn off to display black), but they cannot reach high peak brightness, but again they can achieve high dynamic range by the extremely low black levels.

Now Dynamic Range can be classified as Standard (SDR) or High (HDR). SDR is basically what we consume every day on our smartphones and televisions, SDR doesn’t quite have the peak brightness and colours that HDR brings. HDR along with promising a much higher peak brightness along brings in more colours through its support for 10-bit colour and the Wide Colour Gamut.

What this does is give you inky blanks in a low-light scene while still providing sufficient brightness to light up the subjects face while making sure colours are rendered perfectly.

SDR vs HDR (Source:TFTCentral)


HDR certifications

Now for a display whether it is a monitor or television or a smartphone to qualify for HDR, it has to meet a certain set of criteria as follows.

For televisions, the Ultra HD Alliance says an HDR display is one that can support the following:

  • LCD’s have to output a peak brightness of over 1000 cd/m2 and a black level less than 0.05 cd/m2 (a contrast ratio of at least 20,000:1) 

  • OLED’s have to output a peak brightness of over 540 cd/m2 and a black level less than 0.0005 cd/m2 (a contrast ratio of at least 1,080,000:1)

  • Support 10-bit colour and cover 90% of the DCI-P3 colour gamut

For monitors, the certification standards are a little different with the DisplayHDR coming out with three separate tiers of certifications for LCD monitors for three separate market segments as follows:

  • DisplayHDR 400: Peak brightness of 400 cd/m2, 95% coverage of Rec. 709, 

  • DisplayHDR 600: Peak brightness of 600 cd/m2, 99% coverage of Rec. 709 and 90% coverage of DCI-P3, 10-bit colour support (or 8-bit with 2-bit dithering)

  • DisplayHDR 1000: Peak brightness of 1000 cd/m2, 99% coverage of Rec. 709 and 90% coverage of DCI-P3, 10-bit colour support (or 8-bit with 2-bit dithering)

DisplayHDR criteria

Moving on to smartphones, there is another certification by Ultra HD Alliance exclusive to smartphones, tablets and laptops called Mobile HDR Premium which isn’t limited to just 4K resolution. Mobile HDR Premium has the following criteria:

  • Have a peak brightness of 550 cd/m2 and minimum brightness of 0.0005 cd/m2

  • Should cover 90% of the DCI-P3 colour gamut and have a 10-bit colour depth

MobileHDR criteria


HDR Standards

HDR standards are what is used by streaming services and broadcasters to display content onto your HDR certified display. There following are the four standards currently in use.

HDR10 is an open-source HDR standard that's also the de-facto HDR format that you get with all HDR displays. Basically, every HDR display out there supports HDR 10. HDR10 has support for peak brightness up to 4,000 nits peak brightness, 10-bit colour depth and support for the Rec.2020 colour space.

HDR10 works by using static metadata, which basically tells the TV what is the brightest and the darkest point in a piece of content. When the TV gets this data it fixes this high and low point for the whole movie/ show. The effect of this is the fixed bright and dark point may sometimes cause issues with sure bright or super dark scenes.

Dolby Vision is an improvement over the HDR10 standard and it is designed to offer a much more colourful experience over the HDR10 standard. Dolby Vision has support for up to 10,000 nits peak brightness, 12-bit colour depth and support for the Rec.2020 colour space. 

Dolby Vision operates by using Dynamic Metadata which provides the brightest and darkest point of the content based on each scene (for each frame). This allows for much greater control over the scene due to a more dynamic high and low point which prevents saturation loss or overblowing of a scene.

Static metadata VS Dynamic Metadata (Source: avforums)

Dolby Vision is not royalty-free like HDR10 so the number of Dolby Vision supporting displays are not as much as HDR10 displays, but they are going up in number. All Dolby Vision televisions do support HDR10 so you can easily find HDR10 content, while Dobly Vision content is slowly being available with Netflix and Amazon Prime now supporting it.

HDR10+ is a new standard by Samsung that takes the Dynamic Metadata of Dolby Vision and adds it to the HDR10 standard. So the benefit is you get the Dolby Vision like performance without having to pay royalties. Despite being made by Samsung, any manufacturer can tweak HDR10+ to their liking with only a nominal annual fee for using it. That being said HDR10+ is still based on 10-bit colour support and lacks the 12-bit colour of the Dolby Vision.

HDR10 vs HDR10+ - Static vs Dynamic metadata 

Also, HDR10+ content, for now, is limited to only Amazon Prime when used with a select Samsung Televisions, but Samsung has tied up with 20th Century Fox, Warner Bros., TCL, Hisense and Panasonic for more HDR10+ content and hardware.

HLG or Hybrid Log Gamma is a broadcast-friendly HDR standard created by BBC of UK and NHK of Japan. The reason it was designed was to allow it to be used with SDR displays as well which can reduce costs as you no longer need to broadcast HDR and non-HDR content separately. HLG doesn’t use metadata but supports dynamic colour alteration which can even improve the picture quality of your SDR TV. HLG is supported by Youtube and Satellite television.

Some drawbacks are the fact that even though it works with SDR TV’s, it doesn’t work with all HDR TVs. Next, it doesn't really support the black levels that HDR10 and Dolby Vision support, but it can make the image much brighter and vivid. Also, it uses fixed max brightness and low brightness like HDR10.
 

Verdict and Summary

When HDR was launched, it was meant to be the improvement in dynamic range in the same way, 4K was a resolution improvement to Full HD. When we talk about HDR certifications a lot of certifications do take 4K into account as it goes hand-in-glove with HDR to deliver a much brighter and sharper experience.

But that's not necessarily true today with smartphones like Note 9, Apple iPhone XS Max using 2K resolution displays which are below the 4K resolution with mid-rangers like the Nokia 7.1 using HDR with Full HD resolution. What this does is make the experience much more approachable for all users.

Of the four main HDR standards we have mentioned, HDR10 has the most acceptability and you get the widest range of content for it. In terms of performance, Dolby Vision and HDR10+ are amongst the best in quality but do not have as much content. Finally, HLG is the most backwards-friendly of the standards but its simply not as good in terms of quality as the others.

Also when we talk about standards we have to understand that there will be more and more standards to come. In fact, Technicolor is already at it with three new proposed HDR standards- One similar to HLG designed to work with SDR televisions also (SL-HDR1), one with support for Dynamic Metadata like Dolby Vision (SL-HDR2) and the final one which is based on HLG but supports Dynamic Metadata (SL-HDR3).

Ultimately when you go to buy a new HDR TV what you must look for are three things- the HDR standards supported by the television (HDR10, HLG, Dolby Vision), the content available for those standards (Amazon Prime, Netflix, Satellite TV) and finally, the actual display quality of the television.

The third point (display quality) is paramount as all the HDR standards and certifications only help you know which content supports which display, but even after that you can have a poor quality HDR display which although displays a wider range of colours, may still lack colour accuracy or the high peak brightness may not be uniform across the display which can ruin the picture quality. Ultimately it's up to you to decide what's the best for you and to know more details about display standards keep watching this space.