Hybrid Log-Gamma

Hybrid Log-Gamma (HLG) is a high dynamic range (HDR) standard that was jointly developed by the BBC and NHK. The HLG standard is royalty-free and was approved as ARIB STD-B67 by the Association of Radio Industries and Businesses (ARIB). HLG is compatible with standard dynamic range (SDR) displays. HLG is defined in Digital Video Broadcasting (DVB) UHD-1 Phase 2 and International Telecommunication Union (ITU) Rec. 2100. HLG is supported by HDMI 2.0b, HEVC, and VP9. HLG is supported by video services such as Freeview Play and YouTube.

HLG defines a nonlinear transfer function in which the lower half of the signal values use a gamma curve and the upper half of the signal values use a logarithmic curve.

${\displaystyle E'={\begin{cases}r{\sqrt {E}}\ &0\leq E\leq 1,\!\\a*ln(E-b)+c&1<E\end{cases}}}$

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