Hybrid Log-Gamma

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}

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}

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 2 3 4 "High Dynamic Range" (PDF). European Broadcasting Union. Retrieved 2015-11-01.
  2. 1 2 3 "High Dynamic Range with Hybrid Log-Gamma" (PDF). BBC. Retrieved 2015-11-08.
  3. 1 2 "ARIB STD-B67" (PDF). Association of Radio Industries and Businesses. 2015-07-03. Retrieved 2015-11-01.
  4. 1 2 3 4 5 6 7 8 T. Borer; A. Cotton. "A “Display Independent” High Dynamic Range Television System" (PDF). BBC. Retrieved 2015-11-01.
  5. 1 2 Rajan Joshi; Shan Liu; Gary Sullivan; Gerhard Tech; Ye-Kui Wang; Jizheng Xu; Yan Ye (2016-03-24). "HEVC Screen Content Coding Draft Text 6". JCT-VC. Retrieved 2016-03-26.
  6. 1 2 "Study Group Report High-Dynamic-Range (HDR) Imaging Ecosystem". Society of Motion Picture and Television Engineers. Retrieved 2015-11-30.
  7. ↑ Simon Thompson (2015-05-15). "High Dynamic Range at the SES Industry Days". BBC. Retrieved 2015-11-01.
  8. ↑ Y. Nishida; T. Yamashita; A. Ichigaya; T. Shimizu (2015-06-09). "Proposed addition of transfer characteristics in VUI". JCT-VC. Retrieved 2015-11-01.
  9. ↑ Rajan Joshi; Shan Liu; Gary Sullivan; Gerhard Tech; Jizheng Xu; Yan Ye (2015-09-05). "HEVC Screen Content Coding Draft Text 4". JCT-VC. Retrieved 2015-11-01.
  10. ↑ "Sony Describes Hybrid Log Gamma (HLG) at SMPTE 2015 Event". DisplayDaily. Retrieved 2015-11-03.
  11. ↑ "SMPTE 2015 Annual Technical Conference & Exhibition". Society of Motion Picture and Television Engineers. Retrieved 2015-11-03.
  12. ↑ "Colorfront spotlights amazing UHD HDR performance at SMPTE 2015". American City Business Journals. 2015-10-27. Retrieved 2015-11-01.
  13. ↑ Chris Forrester (2015-11-04). "SkyPerfect offers UHD-HDR by DTH". Advanced Television. Retrieved 2015-11-04.
  14. ↑ Vincent Teoh (2015-11-06). "LG Talk Up 4K OLED TV & HDR at UK Briefing". HDTVtest. Retrieved 2015-11-08.
  15. 1 2 "NASA and Harmonic Explore the Boundaries of UHD at ISS Resupply Launch at Kennedy Space Center". CNN. 2015-12-03. Retrieved 2015-12-05.
  16. ↑ "“Huge success” for UHD-HLG test in Rome". Advanced Television. 2015-12-14. Retrieved 2015-12-18.
  17. ↑ Brian Hallett (2015-12-23). "DaVinci Resolve 12.2 Update & Price Drop". Pro Video Coalition. Retrieved 2015-12-23.
  18. ↑ "LEADER Announces 12G SDI, HDR and Video over IP Options for its LV 5490 and LV 5480 4K-capable Waveform Monitors". CreativeCOW.net. 2016-01-12. Retrieved 2016-01-13.
  19. ↑ Wim Van den Broeck (2016-03-11). "How Avid is Advancing Key Industry Trends Highlighted at the HPA Tech Retreat 2016". Avid Technology. Retrieved 2016-04-04.
  20. ↑ Bryant Frazer (2016-01-29). "Avid Media Composer 8.5 Adds HDR, Simplifies Menus, Offers Better Feedback on the Timeline". studiodaily. Retrieved 2016-04-04.
  21. ↑ "Harmonic Showcases Innovation for Agile Video Delivery at 2016 NAB Show". Yahoo! Finance. 2016-03-29. Retrieved 2016-04-11.
  22. ↑ "Canon reveals new camera and lens in advance of NAB". RedShark. 2016-04-13. Retrieved 2016-04-13.
  23. ↑ "Dome Productions to Begin Trialing of HLG for Delivering HDR". Yahoo! Finance. 2016-04-15. Retrieved 2016-04-15.
  24. 1 2 "Sony Goes Beyond Definition at NAB 2016". PR Newswire. 2016-04-18. Retrieved 2016-04-18.
  25. ↑ "Ultra HD Forum Releases First Industry Guidelines for Deploying End-to-End Live & Pre-Recorded UHD Services in 2016". Business Wire. 2016-04-18. Retrieved 2016-04-18.
  26. 1 2 "End-to-end guidelines for phase A implementation". Ultra HD Forum. 2016-04-18. Retrieved 2016-04-18.

See also

External links

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