Hybrid log–gamma
The hybrid log–gamma (HLG) transfer function is a
HLG is an
Both HLG transfer function and the HLG format are
Description
HLG is designed to be better-suited for
The HLG transfer function is backward compatible with SDR's gamma curve. However, HLG is commonly used with Rec. 2020 color primaries which produce a de-saturated image with visible hue shifts on non-compatible devices.[26] HLG is therefore backward compatible with SDR-UHDTV and will show color distortion on common SDR devices that only support Rec. 709 color primaries.[26]
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.[4][27]
HLG reference OETF is as follows (as defined in ARIB STD-B67):
or as follows (as defined in Rec. 2100):[5]
where
- E is the linear light signal normalized by the reference white levelin the range in ARIB STD-B67 and in the range in Rec. 2100.
- E' is the resulting nonlinear signal
- r is the reference white level and has a signal value of 0.5
- and the constants a, b, and c are defined as a = 0.17883277, b = 1 - 4a = 0.28466892, and c = 0.5 - a ln(4a) = 0.55991073
The signal value is 0.5 for the reference white level while the signal value for 1 has a
HLG reference OOTF is as follows:[5]
- is the luminance of a displayed linear component in cd/m2.
- is a signal for each colour component {Rs, Gs, Bs} proportional to scene linear light normalized to the range .
- is the normalized linear scene luminance.
- is the variable for user gain in cd/m2. It represents LW, the nominal peak luminance of a display for achromatic pixels.
- is the system gamma. = 1.2 at the nominal display peak luminance of 1000 cd/m2.
HLG reference EOTF is as follows:[5]
where
- is the luminance of a displayed linear component in cd/m2.
- is the non-linear electrical signal in the range .
- is the variable for user black level lift.
- is nominal peak luminance of the display in cd/m2 for achromatic pixels.
- is the display luminance for black in cd/m2.
HLG does not need to use
The dynamic range that can be perceived by the human eye in a single image is around 14 stops.[27] An SDR video display with a 2.4 gamma curve and a bit depth of 8-bits per sample can display a range of about 6 stops without visible banding.[27] Professional SDR video displays with a bit depth of 10-bits per sample extend that range to about 10 stops.[27] When HLG is displayed on a 2,000 cd/m2 display with a bit depth of 10-bits per sample it can display a range of 200,000:1 or 17.6 stops without visible banding.[27]
HLG increases the
HLG is supported in Rec. 2100 with a nominal peak luminance of 1,000 cd/m2 and a system gamma value that can be adjusted depending on background luminance.[5][30]
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:[28]
where
- Lc has a nominal range of 0 to 1 and V is the resulting nonlinear signal
- the constants a, b, and c are defined as a = 0.17883277, b = 1 - 4a = 0.28466892, and c = 0.5 - a ln(4a) = 0.55991073
History
Inception
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).[31] 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.[32][12]
Later that year, Sony showed HLG video on a modified HDR display at the SMPTE 2015 conference.[33][34] Colorfront announced that their Transkoder 2016 software would support HDR output using HLG.[35] LG announced that their 2015 4K OLED TVs would support HDR from HLG and perceptual quantizer (PQ).[36] Blackmagic Design released an update for DaVinci Resolve that added support for HLG.
2016
Industry bodies:
- The Ultra HD Forum announced their guidelines for UHD Phase A which includes support for HLG.[41][42] The Ultra HD Forum also defined HLG with a bit depth of 10-bits, and the Rec. 2020 color space.[42]
- The ITU announced Rec. 2100 which defines two HDR transfer functions which are HLG and PQ.[5][30]
- Freeview Play which includes support for HDR using HLG.[16]
- The
- HDMI announced that HLG support had been added to the HDMI 2.0b standard.[11][44][45]
Hardware:
- 12G-SDI waveform monitors with support for HLG.[46]
- Harmonic Inc. released an update for the ViBE 4K UHD encoder that added support for HLG.[47]
- Canon Inc. announced that they will release firmware updates for the DP-V2410 and DP-V3010 reference displays to add support for HLG.[48]
- Sony announced the PVM-X550 OLED monitor with support for HLG.[49] Sony also announced a firmware update for the BVM-X300 OLED monitor to add support for HLG.[49]
- Sony announced that in October they would release a firmware update to add HLG to their BVM-X300 OLED monitor.[50]
- Sony announced that their VPL-VW675ES projector would support HLG.[51]
- The Trusted Reviews website reported that Samsung had told them that all of their 2016 HDR TVs could support HLG with a firmware update.[52]
- Atomos updated their Shogun Inferno product to include HLG input and output for recording, monitoring editing and layout from Cameras and computers as well as to HLG compatible TV's.[53]
Software:
- Avid Technology released an update for Media Composer that added support for HLG.[54][55]
- Google announced Android TV 7.0 which supports HLG.[13][56]
Broadcasters:
- Dome Productions announced that they will begin trials of HLG to deliver HDR content.[57]
- SKY Perfect JSAT Group announced that on October 4 they will start the world's first 4K HDR broadcasts using HLG.[58]
- Eutelsat announced that it will launch a new channel using HLG.[59]
- Google announced that YouTube will start streaming HDR videos which can be encoded with HLG or PQ.[60][15]
- The BBC announced that it was adding a 4-minute HLG edit from their Planet Earth II series to its BBC iPlayer IPTV platform for public UHD testing.[61]
- Mediapro/Overon announced that they will transmit the Spanish Football League (LFP) worldwide using 4K HDR broadcasts based in HLG
2017
Industry bodies:
Hardware:
- LG Corporation announced that their 2017 Super UHD TVs will support HLG.[62]
- Panasonic announced that their 2017 OLED TV will support HLG.[63]
- Sony announced that their 2017 OLED TVs will support HLG.[64]
- JVC announced that their 2017 4K projectors will support HLG.[65]
- LG Corporation announced that they will add support for HLG to their 2016 OLED TVs and their 2016 Super UHD TVs with a firmware update.[66]
- Sony announced that they will add support for HLG to their 2017 4K TVs with a firmware update.[67]
- Panasonic announced that they will add support for HLG to several models of their 2016 4K TVs with a firmware update.[68]
- Philips announced that their 2017 4K TVs will support HLG and that they will add support for HLG to several models of their 2016 4K TVs with a firmware update.[69]
- Sony began releasing firmware updates for several of their 2016 and 2017 Android TV models which adds support for HLG.[70]
- Panasonic released firmware update 2.0 for the Panasonic Lumix DC-GH5 which added support for HLG recording.[71]
- Panasonic began releasing firmware updates for several of their 2016 TV models which adds support for HLG.[72]
- Qualcomm announced the Qualcomm Snapdragon 845 which includes support for HLG.[73]
Software:
- Adobe Systems announced updates to Adobe Creative Cloud which includes support for HLG.[74]
- Final Cut Pro X which includes support for HLG.[75]
Broadcasters:
- Eutelsat announced that their Hot Bird video service would include the Travelxp 4K channel which uses HLG.[76]
- The BBC announced that Blue Planet II would be available in 4K HDR on the BBC iPlayer using HLG.[17] Blue Planet II will be available on the BBC iPlayer service from December 10, 2017 to January 16, 2018.[77] The BBC states that almost 400 TV models have support for HLG which includes TV models from Finlux, Hisense, Hitachi, LG, Panasonic, Philips, Samsung, Sony, and Toshiba.[17][77]
- DirecTV began broadcasting HLG HDR on their 4K Channels 104 and 106.[18][19]
2018
2019
- Panasonic announced HLG support in their S1 and S1R full frame mirrorless cameras which will be released in March 2019.[79]
2020
- Sky UK announced that their popular Sky Q box will get HLG support from May 27, 2020.[80]
- Apple released the iPhone 12 series with HLG video recording support via Dolby Vision profile 8.4, which adds a Dolby Vision metadata layer on top of HLG footage.[81]
See also
- Dynamic range
- Gamma correction
- High-dynamic-range rendering
- High-dynamic-range imaging
- High-dynamic-range video
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External links
- ARIB STD-B67
- T. Borer and A. Cotton, A "Display Independent" High Dynamic Range Television System, BBC Research & Development White Paper WHP 309, September 2015