HLG

Hybrid Log-Gamma (HLG) is an HDR standard for television distribution that was developed by BBC Research & Development and NHK. It was designed to enable high dynamic range broadcasting and streaming without the need for additional metadata, making it well suited for live content and existing broadcast chains. HLG is defined within the ITU-R BT.2100 family of standards and is widely associated with the broader HDR ecosystem alongside PQ-based approaches.

Technically, HLG uses a hybrid transfer function that combines a gamma-like curve for darker areas with a logarithmic progression for brighter regions. This approach allows a wide dynamic range to be encoded and displayed while remaining compatible with conventional SDR displays. Because no scene-by-scene orStatic metadata is required, HDR signals can be carried in a single stream and decoded by televisions regardless of whether they are HDR-capable, preserving backward compatibility.

In terms of color, HLG is specified for use with the wide color gamut standards associated with BT.2100, often leveraging Rec. 2020 primaries, though it can be mapped to other color spaces by the display. The standard is designed to work with both broadcast and streaming environments, enabling HDR content to be viewed on compatible TVs at higher brightness and with expanded color, while SDR devices render a plausible image without special metadata.

Adoption and support have grown across major TV brands, broadcast operators, and streaming platforms, particularly for live events and news, where simplicity and backward compatibility are advantageous. HLG remains one of the primary HDR approaches alongside PQ-based systems such as HDR10 and Dolby Vision.