The HDMI Forum has included support for the third major HDR format, namely HLG (Hybrid Log Gamma), in the HDMI 2.0b standard. HLG has been developed for broadcast TV by UK’s BBC and Japan’s NHK.

HLG support in HDMI 2.0b
The HDMI interface standard already covered the open HDR10 format. Dolby has also built a chip-based solution that can transfer Dolby Vision HDR (with dynamic metadata) over HDMI.

HDMI 2.0b now officially supports the third major HDR format called HLG, which is short for “Hybrid Log Gamma”. It was developed by UK’s BBC and Japan’s NHK for broadcast TV. Since broadcasters have very limited bandwidth, HLG can combine HDR (High Dynamic Range) and SDR (Standard Dynamic Range) in the same TV signal, thus saving broadband for more channels.

A traditional non-HDR TV will ignore the metadata embedded in the signal whereas an HDR TV will detect the extra metadata (if it supports HDMI 2.0b and HLG).

The HDMI Forum says:
- ”NOTICE: Previously, HDMI Specification Version 2.0b (HDMI 2.0b) only supported HDR (High Dynamic Range) video transport in the SMPTE ST 2084 EOTF (as applied in the media profile commonly known as HDR10), by referencing the CTA861.3 specification. The Consumer Technology Association (CTA) has recently notified the HDMI Forum of the adoption of a new version of the CTA-861 Specification, CTA-861-G. This new version provides additional support for HDR Video transport by including (among others) an extension to the static metadata signaling to include the HLG (Hybrid Log Gamma) EOTF. The HDMI Forum has assessed the applicability of the CTA-861-G Specification to HDMI 2.0b. The HDMI Forum has confirmed that the extension of the static metadata signaling to include HLG can be utilized under the existing HDMI 2.0b Specification. This means that HLG Video Transport functionality may be implemented on HDMI 2.0b compliant devices.

HDMI 2.0b is the latest HDMI standard and follows up on HDMI 2.0a that added support for the HDR10 format (and static metadata) in April 2015. HDMI 2.0b is backwards compatible and does not require new cables or connectors. The next version, unofficially called HDMI 2.1, is expected to support dynamic metadata.


TVs need a firmware update
The problem from a consumer standpoint is that most TVs today do not support HLG. 

BBC shed some light on the matter the other day when it announced a trial for ‘Planet Earth II’ in 4K/HDR using the HLG format. At that time, BBC said that only Panasonic 2015 and 2016 TVs were compliant.

LG, Philips, Samsung, and Sony have each demonstrated HLG on 2016 products at trade shows but none of them have committed to release a firmware update to add the functionality.

- Source: HDMI Forum via @UHD4k