HDR: Dolby Vision, HDR10, HLG - What It Means For TV Viewers

What you need to know about HDR formats

LG UH8500 Series Super UHD TV with HDR10 and Dolby Vision
LG UH8500 Series Super UHD TV with HDR10 and Dolby Vision. Image provided by LG Electronics

The number of TV's boasting 4K display resolution has exploded, and for good reason, who doesn't want a more detailed TV image?

Ultra HD - More Than Just 4K Resolution

4K resolution is just one part of what is now referred to now as Ultra HD. In addition to increased resolution, to make the video look better - improved color is one extra factor that has been implemented on many sets, but the other factor that improves picture quality significantly is proper brightness and exposure levels as a result of increased light output in conjunction with a video processing system referred to as HDR.

What HDR Is

The way HDR works is that in the mastering process for selected content destined for theatrical or home video presentation, the full brightness/contrast data captured during the filming/shooting process is encoded into the video signal.

When encoded in a stream, broadcast, or on a disc, the signal is sent to an HDR-enabled TV, the information is decoded, and the High Dynamic Range information is displayed, based on the brightness/contrast capability of the TV. If a TV is not HDR-enabled (referred to as an SDR - Standard Dynamic Range TV), it will simply display the images without the High Dynamic Range information.

Added to 4K resolution and wide color gamut, an HDR-enabled TV (combined with properly-encoded content), can display brightness and contrast levels close to you would see in the real world. This means bright whites without blooming or washout, and deep blacks without muddiness or crushing.

For example, if you have a scene that has very bright elements and darker elements in the same frame, such as a sunset, you will see both the bright light of Sun and the darker portions of the rest of the image with equal clarity, along with all the brightness levels in between.

Since there is a much wide range from white to black, details not normally visible in both the bright and dark areas of a standard TV image are more easily seen on HDR-enabled TVs, which provides a more satisfying viewing experience.

How HDR Implementation Affects Consumers

HDR is definitely an evolutionary step in improving the TV viewing experience, but alas, consumers are faced with four main HDR formats that affect what TVs and related peripheral components and content to buy. These four formats are:

  • HDR10
  • Dolby Vision
  • HLG (Hybrid Log Gamma)
  • Technicolor HDR

Here is a brief rundown of each format.

HDR10

HDR10 is an open royalty-free standard that is incorporated into all HDR-compatible TVs, home theater receivers, Ultra HD Blu-ray players, and select media streamers.

HDR10 is considered more generic as its parameters are applied equally throughout a specific piece of content. In other words, an average brightness range is applied throughout the entire piece of content.

During the mastering process the brightest point vs darkest point in a movie are determined, so when the HDR content is played back all the other brightness levels, no matter which cut or scene is set in relation to the what the min and max brightness is for the entire movie.

However, in 2017, Samsung demonstrated a scene-by-scene approach to HDR, which it refers to as HDR10+ (not to be confused with HDR+ which will be discussed later in this article). Just as with HDR10, HDR10+ is license free.

As of 2017, although all HDR-enabled devices use HDR10, with Samsung, Panasonic, and 20th Century Fox use HDR10 and HDR10+ exclusively.

Dolby Vision

Dolby Vision is the HDR format developed and marketed by Dolby Labs, which combines both hardware and metadata in its implementation. The added requirement is that content creators, providers, and device makers need to pay Dolby a license fee for its use.

Dolby Vision is considered more precise than HDR10 in that its HDR parameters can be encoded scene by scene or frame-by-frame, and can be played back based on the capabilities of the TV (more on this part later). In other words, playback is based on the brightness levels present at a given reference point (such as a frame or scene) rather than limited to the maximum brightness level for the entire film.

On the other hand, the way Dolby has structured Dolby Vision, licensed and-equipped TVs supporting that format also have the ability to decode both Dolby Vision and HDR10 signals (if this capability is “turned on” buy the specific TV maker involved), but a TV that is only compliant with HDR10 is not capable of decoding Dolby Vision signals.

In other words, a Dolby Vision TV also has the ability to decode HDR10, but an HDR10-only TV cannot decode Dolby Vision. However, many content providers that incorporate Dolby Vision encoding in their content also often include HDR10 encoding as well, specifically to accommodate HDR-enabled TVs that may not be compatible with Dolby Vision. On the other hand, if the content source includes only Dolby Vision and the TV is HDR10 compatible only, the TV will just ignore the Dolby Vision encoding and display the image as an SDR (Standard Dynamic Range) image. In other words, in that case, the viewer will not get the benefit of HDR.

TV brands that support Dolby Vision include select models from LG, Philips, Sony, TCL, and Vizio. Ultra HD Blu-ray players that support Dolby Vision include select models from OPPO Digital, LG, Philips, and Cambridge Audio. However, depending on the manufacturing date, Dolby Vision compatibility may need to be added after purchase via a firmware update.

On the content side, Dolby Vision is supported via streaming on select content offered on Netflix, Amazon, and Vudu, as well as a limited number of movies on Ultra HD Blu-ray disc.

Samsung is only major TV brand marketed in the U.S. that does not support Dolby Vision. Samsung TVs and Ultra HD Blu-ray disc players only support HDR10. If this status changes this article will be updated accordingly.

HLG (Hybrid Log Gamma)

HLG (the techie name aside) is an HDR format that is designed for cable, satellite and over-the-air TV broadcasts. It was developed by Japan's NHK and the BBC Broadcasting Systems but is license free.

The main benefit of HLG for TV broadcasters and owners is that it is backward compatible. In other words, since bandwidth space is at a premium for TV broadcasters, using an HDR format such as HDR10 or Dolby Vision would not allow owners of non-HDR equipped TVs (including non-HD TVs) to view the HDR-encoded content, or require a separate channel just for broadcasting HDR content - which is not cost-effective.

However, HLG encoding is just another broadcast signal layer containing added brightness information without the need for specific metadata, that can be placed on top of the current TV signal. As a result, the images can be viewed on any TV. If you don't have an HLG-enabled HDR TV, it will just not recognize the added HDR layer, so you won't get the benefits of the added processing, but you will a standard SDR image.

However, the limitation of this HDR method is that although it provides a way for both SDR and HDR TVs to be compatible with the same broadcast signals, it does not provide as accurate an HDR result if viewing the same content with HDR10 or Dolby Vision encoding.

HLG compatibility is being included on most 4K Ultra HD HDR-enabled TVs (except Samsung) and home theater receivers beginning with the 2017 model year. However, no HLG-encoded content has been made available - this article will be updated accordingly as this status changes.

Technicolor HDR

Of the four major HDR formats, Technicolor HDR is the least known and is only seeing minor use in Europe. Without getting bogged down in the technical details, Technicolor HDR is probably the most flexible solution, as it can be used in both recorded (streaming and disc) and TV broadcast TV applications. It can also be encoded using frame-by-frame reference points.

In addition, in a similar fashion as HLG, Technicolor HDR is backward compatible with both HDR and SDR-enabled TVs. Of course, you will get the best viewing result on an HDR TV, but even SDR TVs can benefit from increased quality, based on their color, contrast, and brightness capabilities.

The fact that Technicolor HDR signals can be viewed in SDR makes it very convenient for both content creators, content providers, and TV viewers. Technicolor HDR is an open standard that is royalty free for any content providers and TV makers to implement.

Tone Mapping

One of the problems in implementing the various HDR formats on TVs is the fact that not all TVs have the same light output characteristics. For example, a high-end HDR-enabled TV might the ability to output as much as 1,000 nits of light (such as some high-end LED/LCD TVs), while others may have maximum of 600 or 700 nits light output (OLED and mid-range LED/LCD TVs), while some lower-priced HDR-enabled LED/LCD TVs may only output about 500 nits.

As a result, a technique, known as Tone Mapping is used to address this variance. What happens is that the metadata placed in a specific movie or program is remapped to the TVs capabilities. This means that the brightness range of the TV is taken into consideration and adjustments are made to peak brightness and all of the intermediate brightness information, in conjunction with the detail and color present in the original metadata in relation to the range of the TV. As a result, the peak brightness encoded in the metadata is not washed out when shown on TV with less light output capability.

SDR-to-HDR Upscaling

Since the availability of HDR-encoded content is not plentiful yet, Several TV brands are making sure that the extra money consumers spend on an HDR-enabled TV does not go waste by including SDR-to-HDR conversion. Samsung labels their system as HDR+ (not to be confused with HDR10+ discussed earlier), and Technicolor labels their system as Intelligent Tone Management.

However, just as with resolution upscaling and 2D-to-3D conversion, HDR+ and SD-to-HDR conversion do not provide an accurate result as native HDR content. In fact, some content may look too washed out or uneven from scene to scene, but it does provide another way to take advantage of an HDR-enabled TVs' brightness capabilities. HDR+ and SDR-to-HDR conversion can be turned on or off as desired. SDR-to-HDR upscaling is also referred to as Inverse Tone Mapping.

In addition to SD-to-HDR upscaling, LG incorporates a system it refers to as Active HDR processing into a select number of its HDR-enabled TVs which adds onboard scene-by-scene brightness analysis to both HDR10 and HLG content, which improves the accuracy of those two formats.

The Bottom Line

The addition of HDR definitely elevates the TV viewing experience and as format differences are addressed and content becomes widely available across the disc, streaming, and broadcast sources, consumers will accept it just as they have for previous advances (except maybe for 3D).

Although HDR is being applied only in combination with 4K Ultra HD content, the technology is actually independent of resolution. This means that, technically, it can be applied to other resolution video signals, whether it be 480p, 720p, 1080i, or 1080p. This also means that owning a 4K Ultra HD TV doesn't automatically mean that it is HDR-compatible - a TV maker has to make an assertive decision to include it.

However, the emphasis by content creators and providers has been to apply HDR capability within the 4K Ultra HD platform. With the availability of non-4K ultra HD TVs, DVD, and standard Blu-ray disc players diminishing, and with the abundance of 4K Ultra HD TVs as well as increased number of Ultra HD Blu-ray Players available, along with the forthcoming implementation of ATSC 3.0 TV broadcasting, the time and financial investment of HDR technology is best suited for maximizing the value of 4K Ultra HD content, source devices, and TVs.

Although in its current implementation stage there seems to be a lot of confusion, don't panic. The main thing to keep in mind is that even though there are subtle quality differences between each format (Dolby Vision is considered to have a slight edge so far), all the HDR formats provide a significant improvement in the TV viewing experience.