Topics covered in this article:
- Setting Up the Color Correction System
- Importing Source Material
- The Working Colorspace and EOTF
- Monitoring for HDR Color Grading
Importing Source Material into the Color Correction System
Different types of material are typically used as sources for a project. These can include:
- Live images acquired using different types of cameras (film or digital cinema cameras, DSLRs, action cameras like GoPro, etc.)
- CGI material that is generated digitally on a computer
From a color correction perspective, the above sources can be received at bit depths ranging from 8 to 16 bits per pixel in various formats like:
- Camera RAW (.ari, .r3d, .arw, .srf, .crw, etc.)
- Images (TIFF, DPX, OpenEXR, etc.)
- Video files (Apple ProRes, etc.)
More details about recommended source material for creating high-quality Dolby Vision content can be found in this article FAQ: Dolby Vision Recommended Source Formats (force.com)
While different color correction systems work differently, the source material must be imported correctly into the color correction system without losing any valuable image data during the image import/conversion process. Color correction systems usually have their own proprietary color management workflows and techniques that involve a combination of look-up tables (LUTs) and/or transforms to first import the material into the system and then ensure that they are manipulated/modified efficiently and without degradation. Remember to modify existing SDR LUTs for PQ work as they they will produce undesirable results in a PQ workflow.
Working Colorspace and EOTF
For output (rendering), Dolby recommends a combination of P3 (colorspace), D65 (whitepoint), and PQ/ST2084 (EOTF) for Dolby Vision content creation and delivery. Some studios may request Rec2020 deliverables, in which case a combination of Rec2020 (colorspace), D65 (whitepoint), and PQ/ST2084 (EOTF) may be used. When using Rec2020, we recommend limiting the output colorspace to P3 within the Rec2020 container since reference displays today are not capable of displaying the entire Rec2020 gamut. The P3 limiter can be set up within the color management settings on most color correction systems today.
The colorist and/or the post production facility may choose to work in a scene referred workspace instead of a display referred workspace like PQ. If so, the color correction system can be setup to have a scene referred workspace and the color corrector will respond accordingly during the color correction process. The output of the color correction system must be setup for P3D65 or Rec2020 and PQ/ST2084 for all Dolby Vision Master deliverables.
Monitoring for HDR Grading and Dolby Vision – HDR Master Reference Display / Target Reference Display
The HDR master reference monitor must be calibrated and set up to match the color pipeline that is being used on the color correction system. So, if the output is set for P3D65, the HDR monitor must be set up for P3D65 as well.
The Target Reference display must also be calibrated and set up to match the target that is selected on the CMU (iCMU/eCMU). So, if the CMU is set to a Rec709/100 nits/Gamma 2.4 target, the Target Reference display must also be set for Rec709/100 nits/Gamma 2.4. It is important to note that when creating trims for a 600-nit/PQ/P3 (or Rec2020) target, the HDR reference display used can simply be switched into PQ mode and does not require a specific constraint or calibration for 600 nits specifically. The CMU will map the signal to 600nits and the PQ reference monitor will display the 600nit image correctly.
It is important to note that the CMU output is always full range video, and the Target Reference display must therefore be set up for monitoring a full range video signal.
Monitoring for HDR Grading – Waveforms and Scopes
Scopes and/or waveform monitors are extremely important for HDR color grading. HDR scopes must be capable of displaying a PQ video signal correctly with the ability to show a luminance range of 0 to 10,000 nits. We recommended you use two sets of scopes: one to monitor the HDR video signal and the other to monitor the output of the CMU. For the second set of scopes to monitor the output of the CMU, the ability to monitor a PQ signal may be required if trims at 600 nit/PQ are requested by the studio.
Figure 1: HDR/PQ Scopes
Figure 2: SDR Scopes