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HLG Curve

A hybrid log-gamma transfer function for backward-compatible HDR broadcasting.


HLG Curve

Definition

Hybrid Log-Gamma (HLG) is an HDR transfer function jointly developed by BBC and NHK that combines a logarithmic curve for high luminance with a gamma curve for low levels. This design enables HDR signals to be displayed in SDR systems without special metadata.

Technical Characteristics

HLG uses a 10-bit signal where the breakpoint between gamma and log segments sits around 50% code value. The logarithmic tail compresses highlights up to ~1,000 cd/m², while the gamma head preserves shadow detail.

Applications

HLG is widely used in live broadcast, sports, and news where backward compatibility with SDR receivers is essential. It requires no scene-metadata, simplifying workflows for real-time production and distribution.


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