Hybrid Log-Gamma

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Hybrid Log-Gamma (HLG) is a high dynamic range (HDR) standard that was jointly developed by the BBC and NHK.[1] The HLG standard is royalty-free and was approved as ARIB STD-B67 by the Association of Radio Industries and Businesses (ARIB).[1][2][3] HLG is compatible with standard dynamic range (SDR) displays.[1]

Chart showing a conventional SDR gamma curve and Hybrid Log-Gamma (HLG). HLG uses a logarithmic curve for the upper half of the signal values which allows for a larger dynamic range.

Technical details

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.[3][4]

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

  • where E is the signal normalized by the reference white level and E' is the resulting nonlinear signal
  • where r is the reference white level and has a signal value of 0.5
  • where a = 0.17883277, b = 0.28466892, and c = 0.55991073

The signal value is 0.5 for the reference white level while the signal value for 1 has a relative luminance that is 12 times higher than the reference white level.[4] ARIB STD-B67 has a nominal range of 0 to 12.[5] HLG uses a logarithmic curve for the upper half of the signal values due to Weber's law.[4]

HLG does not need to use metadata since it is compatible with both SDR displays and HDR displays.[1][2] HLG can be used with displays of different brightness in a wide range of viewing environments.[2]

The dynamic range that can be perceived by the human eye in a single image is around 14 stops.[4] SDR video with a 2.4 gamma curve and a bit depth of 8-bits per sample has a dynamic range of about 6 stops.[4] Professional SDR video with a bit depth of 10-bits per sample has a dynamic range of about 10 stops.[4] When HLG is displayed on a 2,000 cd/m2 display with a bit depth of 10-bits per sample it has a dynamic range of 200,000:1 or 17.6 stops.[4]

HLG increases the dynamic range of the video compared to a conventional gamma curve by using a logarithmic curve for the upper half of the signal values.[4] HLG also increases the dynamic range by not including the linear part of the conventional gamma curve used by Rec. 601 and Rec. 709.[6] The linear part of the conventional gamma curve was used to limit camera noise in low light video but is no longer needed with HDR cameras.[6]

HLG is supported in HEVC with a formula that is mathematically equivalent to ARIB STD-B67 but has a nominal range of 0 to 1 instead of 0 to 12:[5]

V=\begin{cases} a * ln(12 * L_c - b) + c & 1 \ge L_c > \frac{1}{12},\!\\ sqrt(3) * L_c^{0.5} & \frac{1}{12} \ge L_c \ge 0 \end{cases}

  • where Lc has a nominal range of 0 to 1 and V is the resulting nonlinear signal
  • where a = 0.17883277, b = 0.28466892, and c = 0.55991073

History

On May 15, 2015, the BBC announced that they had begun work with the NHK to develop a joint HDR proposal that would be proposed to the International Telecommunication Union (ITU).[7]

On June 9, 2015, HLG was proposed to the JCT-VC for High Efficiency Video Coding (HEVC) and added to the June 2015 draft of the screen content coding extensions.[8][9]

On October 26, 2015, Sony showed HLG video on a modified HDR display at the SMPTE 2015 conference.[10][11]

On October 27, 2015, Colorfront announced that their Transkoder 2016 software would support HDR output using HLG.[12]

On November 4, 2015, SKY PerfecTV! announced that they will use HLG to transmit 4K UHDTV HDR programming to their satellite subscribers in Japan.[13]

On November 6, 2015, LG announced that their 2015 4K OLED TVs would support HDR from HLG and SMPTE ST 2084.[14]

On December 3, 2015, Harmonic Inc. and NASA announced the HDR capture of a Atlas V launch which was broadcast the next day on NASA TV using HLG.[15] UHDTV HDR video clips will be published early next year in both HDR10 and HLG.[15]

On December 14, 2015, Vatican Television Center broadcast the ceremony of the Holy Door using HLG and the Rec. 2020 color space.[16]

On December 23, 2015, Blackmagic Design released an update for DaVinci Resolve that added support for HLG.[17]

2016

On January 12, 2016, Leader Electronics Corporation announced their 12G-SDI waveform monitors with support for HLG.[18]

On January 29, 2016, Avid Technology released an update for Media Composer that added support for HLG.[19][20]

On March 29, 2016, Harmonic Inc. released an update for the ViBE 4K UHD encoder that added support for HLG.[21]

On April 13, 2016, Canon Inc. announced that they will release firmware updates for the DP-V2410 and DP-V3010 reference displays to add support for HLG.[22]

On April 15, 2016, Dome Productions announced that they will begin trials of HLG to deliver HDR content.[23]

On April 18, 2016, Sony announced the PVM-X550 OLED monitor with support for HLG.[24] Sony also announced a firmware update for the BVM-X300 OLED monitor to add support for HLG.[24]

On April 18, 2016, the Ultra HD Forum announced their guidelines for UHD Phase A which includes support for HLG.[25][26] The Ultra HD Forum also defined HLG10 as HLG, a bit depth of 10-bits, and the Rec. 2020 color space.[26]

References

  1. ↑ 1.0 1.1 1.2 1.3 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ 15.0 15.1 Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ 24.0 24.1 Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ 26.0 26.1 Lua error in package.lua at line 80: module 'strict' not found.

See also

External links

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