HLG Look-Up Table Licensing

Transcription

1 HLG Look-Up Table Licensing Part of the HDR-TV series. Last updated July 218 for LUT release v1.2. Introduction To facilitate the introduction of HLG production, BBC R&D are licensing a package of look-up tables (LUTs) which implement a range of key format conversions. The conversions are implemented as 33-cube 3D-LUTs and include: BT.21 PQ (1 cd/m 2 peak) to BT.21 HLG BT.21 PQ (4 cd/m 2 peak) to BT.21 HLG BT.79 (SDR) to BT.21 HLG (display-referred mapping maintaining SDR "look") BT.79 (SDR) to BT.21 HLG (scene-referred mapping for matching cameras) BT.79 (SDR) to BT.21 HLG (display-referred up-conversion for SDR "look") BT.79 (SDR) to BT.21 HLG (scene-referred up-conversion for matching cameras) BT.21 HLG to BT.21 PQ (1 cd/m 2 peak) BT.21 HLG to BT.79 (SDR) (display-referred mapping maintaining HDR "look") BT.21 HLG to BT.79 (SDR) (scene-referred mapping to match conventional SDR cameras) (added in release v1.2) S-Log3 SR-Live to BT.21 HLG Test LUTs to verify the correct operation of LUT hardware (added in release v1.2) Additional conversions may be added in the future. As part of the package we also offer a 65-cube 3D-LUT for loading into a Dolby PRM-42/422 display, to add support for BT.21 HLG. LUT Details The complete list of conversions and variants is shown in Tables 3a, 3b and 3c. New LUTs that have been added or improved as part of the version 1.2 update are highlighted in blue and bold. More details are given in the Revision History section at the end of this document. Three types of LUT are included, that scale the input and output video in different ways: - Type I LUTs are intended for software applications, and older hardware LUTs that do not support full-range SDI signals; - Type II LUTs are intended for full-range SDI input signals such as S-Log3 and those produced by some PQ devices; BBC 218. All rights reserved.

2 - Type III LUTs are intended for the majority of broadcast TV applications, where it is important to pass the sub-blacks 1 and super-whites 2 of narrow-range signals (e.g. ITU-R BT.814 HDR PLUGE and ITU-R BT.2111 HDR Colour Bars). The three LUT types are illustrated in Figures 1 to 3: Type I Input Signal Range: LUT Mode: Output Signal Range: Nominal input signal and processing range Output signal and processing range Input Normalisation ( - 1) D-LUT Scale Output ( - 94) 94 Output Figure 1- Type I signal scaling, primarily intended for software-based LUT applications Type II Input Signal Range: Full LUT Mode: Full Output Signal Range: Processing range Input Input signal and processing range Normalisation ( - 1) 3D-LUT Scale Output ( - 123) Clip to SDI Range 94 Nominal output signal range Output 4 Figure 2 - Type II signal scaling, intended for full-range input signals (e.g. S-Log3) Type III Nominal input signal range 123 Input Signal Range: 123 LUT Mode: Full 1 Output Signal Range: Processing range Input Normalisation ( - 1) 3D-LUT Scale Output ( - 123) Clip to SDI Range Nominal output signal range Output 4 Figure 3 - Type III signal scaling, primarily intended for hardware-based LUT applications The Type II full-range mode LUT is used to convert full-range PQ and S-Log3 signals to HLG. So full-range Type II versions of the PQ1, PQ4, S-Log3 (1%) and S-Log3 (2%) 1 signals below 1-bit code value 2 signals above 1-bit code value 94 BBC 218. All rights reserved.

3 conversion LUTs are provided. We recommended only narrow-range signals with HLG, to improve interoperability, maintain signal fidelity and reduce the likelihood of errors in production. So even when a hardware LUT device is operated in full-range mode, the HLG output signal is always offset and scaled within the LUT to lie within the usual narrow signal range of to 94 (1-bits). Scene-Light vs Display-Light Conversions Most SDR/HDR format conversions are based on display-light. By that we mean that the conversion calculates the light produced by the signal on a reference display in the original format, and attempts to produce a similar light output on a reference display operating in the new output format. Display-light conversions maintain the original look of the pictures after conversion. So display-light conversions work well for graded content, where it is important to maintain the artistic intent. However, for live programming, the displayed look of SDR BT.79, SDR BT.22, BT.21 HLG, BT.21 PQ and S-Log3 (SR-Live) formats are all different. By that we main that the displayed colour saturation, hue and luminance of objects in the scene are different for each signal format. That is because each format specifies a different end-to-end opto-optical transfer function (the relationship between light falling on a camera sensor and the light emitted by the display). So, a display-light conversion will make it very difficult to colour match SDR and HDR cameras. By contrast, scene-light conversions calculate the light falling on the camera sensor, which is the same regardless of the signal format. So scene-light conversions work very well when trying to match SDR and HDR cameras, as part of a large live TV production. Scene-light conversions are also useful for HDR to SDR conversion, where the desire is to match the look of a traditional SDR camera. In release v1.2 we have introduced a new a scene-light conversion from BT.21 HLG to SDR BT.79 (LUT 12). The conversion is particularly useful when a production is required to provide both an HLG HDR output, and an SDR BT.79 output that closely resembles that of a traditional SDR BT.79 camera. The scene-light conversion allows the HLG cameras to be shaded (racked) their CCU SDR output, with the HLG HDR output following the SDR with a suitable fixed gain offset. Only the HLG HDR signal need be passed through the production switcher, as the new LUT is then used to convert the switcher output to an SDR BT.79 signal that very closely resembles the CCU SDR signal with which the cameras were shaded. More details can be found in section of ITU-R report BT.248, Operational Practices in HDR Television Production. When matching SDR BT.79 cameras with BT.21 HLG cameras, significantly better results can be obtained if the signal clippers on the SDR cameras are relaxed to EBU Technical BBC 218. All rights reserved.

4 Recommendation R13 signal levels (-5%/+15%) and the conversion process takes account of the signals in the sub-blacks and super-whites. The sub-black and super-white signals produced by many cameras effectively increase the dynamic range and colour gamut of the camera. In order to exploit the extended SDR signal range, the conversion LUT has to operate in fullrange mode, taking account of the black level offset of the SDR input signals (1-bit code value ) (LUT Type III). Because of the improved performance, the scene-referred BT.79 to BT.21 HLG camera mapping LUT (LUT 4) and camera up-conversion LUT (LUT 5) are only provided in full-range mode (Type III) versions. Output Signal Clipping Output signals for Type I LUTs are clipped in the range to 1. Once scaled, the SDR output signals for LUTs 8c, 8d are clipped within the look-up table to EBU Technical Recommendation R13 signal levels. The remaining Type II and Type III LUTs with PQ or HLG outputs are clipped to fullrange, to ensure that they pass ITU-R BT.2111 HDR Colour Bars. External processing, illustrated in Figure 2 and 3, is necessary to clip the LUT output to 1-bit SDI range (4 to 119). Note that, due to the limited accuracy of look-up table interpolation algorithms, the output black level of Type II and Type III LUTs may not always be exactly 1-bit code value. Colour Matrices Many hardware LUT devices assume BT.79 colour when converting between the Y C BC R signals carried on SDI interfaces and the R G B signals required by the look-up tables. When no option is available to select the correct BT.22/BT.21 colour for the HDR signals, a correction can be applied within the look-up table itself, illustrated in Figure 4. Tables 3a, 3b and 3c indicate whether a LUT file includes the BT.79 colour compensation. BT.21 signal to BT.79 to BT.79 (via LUT) to BT.21 (via LUT) PQ to HLG transform LUT processing to BT.21 (via LUT) to BT.79 (via LUT) to BT.79 BT.21 signal Figure 4 - Example of colour compensation within a LUT. This example shows a PQ to HLG conversion (LUT 1b, 1d, 2b or 2d). Software packages that support conversion LUTs, such as colour grading software, can usually be configured to use the correct BT.22/BT.21 colour primaries, normalise full-range and narrow-range input signals to a common range for their internal processing, and clip super-white and sub-black signals to lie within that range. So only a single Type I LUT (which is the same as BBC 218. All rights reserved.

5 the narrow mode hardware LUT without BT.79 colour compensation) is necessary for most software applications. LUTs for Testing Hardware In order to test that LUT hardware is correctly configured, we have developed four special LUTs (13a, 13b, 13c & 13d) that can be used to confirm the correct input/output scaling and colour processing. LUTs 13b, 13c & 13d output a fixed RGB triplet for any input value. They are used to confirm the LUT output-side processing. LUT 13a is a pass-though LUT. Once the output-side processing is known to be correct, the pass-through LUT can be used to confirm complementary processing on the input-side. When both input and output colour matrices are configured for the same colour space (BT.79 or BT.22/BT.21) and scaling, signals should pass through the LUT hardware almost transparently (with some interpolation errors) when loaded with the pass-through LUT 13a. Particular care is necessary when configuring the LUT hardware as the scaling of C B' and C R' colour components is different for full-range and narrow-range BT.21 signals (see Table 9 of ITU-R BT.21). All BBC LUTs output narrow range signals, even when the LUT is operating in full-range mode. So the narrow-range colour component scaling should be used. LUTs 1c & 1d and 2c & 2d (Type II LUTs) are designed for full-range PQ inputs signals, but narrow-range output signals. So different scaling the of C B' and C R' colour components should be used on input and output. We have not yet developed a test for LUT hardware loaded with these LUTs. Tables 1 & 2 illustrate the expected Y'Cb'Cr' 1-bit code values (decimal) on the SDI output for different combinations of colour and LUT mode. Rounding errors of +/- 1 lsb (least significant bit) should be expected. Table 1- range mode LUT output on Y'Cb'Cr' SDI LUT Filename LUT Output Values Type I - Range LUT Mode (1-bit decimal - 94) BT.22/BT.21 Colour BT.79 Colour R' G' B' Y' Cb' Cr' Y' Cb' Cr' 13b_static_-_-5_1-.cube c_static_-4_-5_-6.cube d_static_-125_-5_-875.cube Table 2- Full range mode LUT output on Y'Cb'Cr' SDI for narrow range signals LUT Filename LUT Output Values TYPE III - Full Range LUT Mode (1-bit decimal - 123), Range Output Signals (1-bit decimal - 94) BT.22/BT.21 Colour BT.79 Colour R' G' B' Y' Cb' Cr' Y' Cb' Cr' 13b_static_-_-5_1-.cube c_static_-4_-5_-6.cube d_static_-125_-5_-875.cube BBC 218. All rights reserved.

6 Licensing Options Two licences are available. The first licence is intended for manufacturers wishing to either embed the LUTs within their products, or include the LUTs with their products. The second licence is intended for broadcasters and production facilities, where the LUTs are to be loaded into existing equipment or software tools. Please for details. BBC 218. All rights reserved.

7 No. From To Comment Variant LUT 1 PQ 1 BT.21 HLG Type III recommended for hardware as 3 BT.79 BT.21 HLG 4 BT.79 BT.21 HLG they pass sub-blacks and super-whites (e.g. BT.2111 Colour Bars). 2 PQ 4 BT.21 HLG Luminance tone-mapping. Type III recommended for hardware as they pass sub-blacks and super-whites (e.g. BT.2111 Colour Bars). Display-referred mapping maintaining SDR "look". 1% SDR maps to 75 % HLG (HDR Reference White - see ITU- R BT.248 and BT.239). Recommended for matching the displayed colour of SDR graphics. Type III preferred for hardware as they pass sub-blacks and super-whites. Scene-referred mapping. Recommended for matching SDR graphics with in-vision branding. 1% SDR maps to 75 % HLG (HDR Reference White - see ITU-R BT.248 and BT.239) Table 3a - LUT conversions and variants. Type LUT Mode Input Signal Range Output Signal Range BT.79 colour LUTs for software BT.79 colour Filename a I No No 1a_PQ1_HLG_mode-nar_in-nar_out-nar_nocompb I Yes 1b_PQ1_HLG_mode-nar_in-nar_out-nar_withcompc II Full Full No 1c_PQ1_HLG_mode-full_in-full_out-nar_nocompd II Full Full Yes 1d_PQ1_HLG_mode-full_in-full_out-nar_withcompe III Full f III Full No 1e_PQ1_HLG_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 1f_PQ1_HLG_mode-full_in-nar_out-nar_withcompv1_2.cube a I No No 2a_PQ4_HLG_mode-nar_in-nar_out-nar_nocompb I Yes 2b_PQ4_HLG_mode-nar_in-nar_out-nar_withcompc II Full Full No 2c_PQ4_HLG_mode-full_in-full_out-nar_nocompd II Full Full Yes 2d_PQ4_HLG_mode-full_in-full_out-nar_withcompe III Full f III Full No 2e_PQ4_HLG_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 2f_PQ4_HLG_mode-full_in-nar_out-nar_withcompv1_2.cube a I No No 3a_BT79_HLG_DISPLAY_mode-nar_in-nar_out-nar_nocompb I Yes 3b_BT79_HLG_DISPLAY_mode-nar_in-nar_outc III Full d III Full a III Full b III Full LUTs for hardware No 3c_BT79_HLG_DISPLAY_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 3d_BT79_HLG_DISPLAY_mode-full_in-nar_outnar_withcomp-v1_2.cube No 4a_BT79_HLG_SCENE_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 4b_BT79_HLG_SCENE_mode-full_in-nar_out-nar_withcompv1_2.cube BBC 218. All rights reserved.

8 No. From To Comment Variant LUT 5 BT.79 BT.21 HLG 6 BT.79 BT.21 HLG 7 HLG PQ 1 Display-referred up-conversion for SDR "look". Recommended for graded content. Type III preferred for hardware as they pass subblacks and super-whites. Scene-referred SDR to HDR upconversion. Recommended for matching SDR and HDR cameras in live production. Matched with LUT 8 (display-light "downconversion"). Type III recommended for hardware as they pass sub-blacks and super-whites (e.g. BT.2111 Colour Bars). 8 HLG BT.79 Display-light conversion, with a baseline hard gamut clip. Recommended for preserving the HDR "look" in SDR. Matched with LUT 6 (display-light "upconversion"). Table 3b - LUT conversions and variants. Type LUT Mode Input Signal Range Output Signal Range BT.79 colour LUTs for software BT.79 colour Filename a I No No 5a_BT79_HLG_UPCONVERT_DISPLAY_ mode-nar_innar_out-nar_nocomp-v1_2.cube c III Full d III Full a III Full b III Full b I Yes 5b_BT79_HLG_UPCONVERT_DISPLAY_mode-nar_innar_out-nar_withcomp-v1_2.cube No 5c_BT79_HLG_UPCONVERT_DISPLAY_mode-full_innar_out-nar_nocomp-v1_2.cube Yes 5d_BT79_HLG_DISPLAY_UPCONVERT_mode-full_innar_out-nar_withcomp-v1_2.cube No 6a_BT79_HLG_UPCONVERT_SCENE_mode-full_in-nar_outnar_nocomp-v1_2.cube Yes 6b_BT79_HLG_UPCONVERT_SCENE_mode-full_in-nar_outnar_withcomp-v1_2.cube a I No No 7a_HLG_PQ1_mode-nar_in-nar_out-nar_nocompb I Yes 7b_HLG_PQ1_mode-nar_in-nar_out-nar_withcompc III Full d III Full No 7c_HLG_PQ1_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 7d_HLG_PQ1_mode-full_in-nar_out-nar_withcompv1_2.cube a I No No 8a_HLG_BT79_mode-nar_in-nar_out-nar_nocompb I Yes 8b_HLG_BT79_mode-nar_in-nar_out-nar_withcompc III Full d III Full LUTs for hardware No 8c_HLG_BT79_mode-full_in-nar_out-nar_nocompv1_2.cube Yes 8d_HLG_BT79_mode-full_in-nar_out-nar_withcompv1_2.cube BBC 218. All rights reserved.

9 R=., G=.5, B=1. c N/A N/A N/A N/A No 13c_static_-4_-5_-6.cube R=.125, G=.5, B=.875 d N/A N/A N/A N/A No 13d_static_-125_-5_-875.cube No. From To Comment Variant LUT 1 S-Log3 (1%) BT.21 HLG BT.22 colour. 1% S-Log3 (9% reflectance) maps to 73 % HLG (see BT.248). 11 S-Log3 (2%) BT.21 HLG Typical SR-Live. 2% S-Log3 (9% 12 HLG BT.79 Scene-light conversion, with a 13 For testing LUT hardware reflectance) maps to 73% HLG. baseline hard gamut clip. Recommended for matching the SDR camera CCU output in live production. Table 3c - LUT conversions and variants. Type LUT Mode Input Signal Range Output Signal Range BT.79 a II Full Full b II Full Full a II Full Full b II Full Full colour LUTs for software BT.79 colour Filename No No 1a_S-Log3_1pc_HLG_mode-full_in-full_out-nar_nocompv1_2.cube Yes 1b_S-Log3_1pc_HLG_mode-full_in-full_out-nar_withcompv1_2.cube No No 11a_S-Log3_2pc_HLG_mode-full_in-full_out-nar_nocompv1_2.cube Yes 11b_S-Log3_2pc_HLG_mode-full_in-full_out-nar_withcompv1_2.cube a I No 12a_HLG_BT79_SCENE_mode-nar_in-nar_outb I Yes 12b_HLG_BT79_SCENE_mode-nar_in-nar_outc III Full d III Full LUTs for hardware No 12c_HLG_BT79_SCENE_mode-full_in-nar_outnar_nocomp-v1_2.cube Yes 12d_HLG_BT79_SCENE_mode-full_in-nar_outnar_withcomp-v1_2.cube Pass-through LUT a N/A N/A N/A N/A No 13a_pass-through.cube R=., G=.5, B=1. b N/A N/A N/A N/A No 13b_static_-_-5_1-.cube BBC 218. All rights reserved.

10 Revision History LUT Date Comments Release 1. 22/12/17 Initial release /3/18 Adds S-Log3 to HLG conversion Adds several Type III LUTs to pass sub-blacks and superwhites Corrects a small black level offset for PQ LUTs 1c, 1d and 2c, 2d, 7a and 7b 1.2 2/7/18 SDR scene-light mapping to HLG (LUT 4) now maps 1% SDR to 75% HLG rather than 73%, to align with recommendations in ITU-R Report BT.239. Improves the round-tripping performance of the display-light SDR to HLG up-conversion (LUT 5) and HLG to SDR down-conversion (LUT 8). Improves the colour space conversion of the display-light HLG to SDR down-conversion (LUT 8) Adds LUT 12 for scene-light HLG to SDR conversion, to mimic the SDR output of a camera CCU. Adds LUTs 13a, 13b, 13c and 13d for testing LUT hardware. Minor improvement to the accuracy of all full-range LUT conversions. BBC 218. All rights reserved.