Topics covered in this article:
- Preparation for Dolby Vision Analysis
- Selecting the HDR mastering display
- Selecting the active image area
Once the color correction system and other ancillary equipment are set up correctly, color grading the HDR master is similar in many ways to grading in SDR. The higher dynamic range, the expanded contrast, and the wider color gamut provide a much larger canvas to tell visually compelling stories unlike ever before, but in essence, the colorist is tasked with creating beautiful images that conform to the creative intent and the story that is being told.
Having completed the HDR grade, the project can now be delivered as an HDR master, but it will not fulfill the requirements of a finished Dolby Vision Master. To deliver a Dolby Vision Master, the following steps will have to be completed:
- Preparation for Dolby Vision Analysis
- Create L1 metadata using Dolby Vision Analysis
- Check the L1 metadata using Dolby Content Mapping (CMU)
- Performing the necessary modifications to the metadata through the Trim Pass thereby creating L2/L3/L8 metadata (optional)
Preparation for Dolby Vision Analysis
There are a few preliminary steps that have to be performed before running the Dolby Vision Analysis:
1. Install Dolby Vision license
A license must be installed on the Resolve system to activate the Dolby Vision trim controls. This license can be obtained from Dolby, and it will be sent via email with installation instructions.
2. Enable Dolby Vision
On Resolve, Dolby Vision must be “enabled” in Project Settings to activate the Dolby Vision control panel on the color page.
3. Select Dolby Vision version
The version of Dolby Vision must be selected based on the guidance from the studio that owns and/or commissions the project.
4. Select HDR mastering monitor
The HDR mastering display used for the project must be specified in the Mastering Display selection field under Dolby Vision settings. The monitor selection that is made is recorded as part of the L0 metadata in the exported Dolby Vision XML and is important in the calculations and algorithms used in Dolby Vision mapping.
Note: If the mastering monitor being used is not listed, the closest one may be used. For example, if a 3000-nit P3 mastering monitor is being used for the project, the 4000-nit, P3, D65 option may be selected as the Mastering Display.
5. Set Blanking/Letterbox as required
Dolby Vision, by design, has metadata (L0/L5) that describes the active image area and the portion of the image that has a letterbox (or blanking). Dolby Vision mapping algorithms (and subsequently playback devices) are designed to apply mapping only in the active image area. This works well for many devices but on HDMI-based devices like set-top boxes and Blu-ray players, this metadata is ignored as the letterbox or blanking areas of the image are used to present subtitles and other graphics to the end user. Due to this implementation on these devices, any positive lift applied to Dolby Vision content during the “trim pass,” will raise the black levels in the letterbox/blanking areas of the image and can become distracting to the end user. Dolby recommends a maximum positive lift value of 0.025 while doing the trims on letterboxed content during the Dolby Vision content creation process.
[Refer to this article - https://professionalsupport.dolby.com/s/article/Trim-Metadata?language=en_US]
Before the analysis is performed, it is important to define the active image area for two very important reasons:
- The Dolby Vision Analysis tools must be instructed to analyze only the active image area and avoid the letterbox (or blanking). Analyzing the black of the letterbox will produce incorrect Minimum (min) values in the L1, which should ideally be derived by analyzing the lowest black level in the active image area of the shot.
- When the active image area is selected correctly, it is recorded in the Dolby Vision metadata and will be included as L0/L5 metadata in the exported Dolby Vision XML.
While other systems will have their own respective ways of doing this, there are two ways to set the active image area in Resolve:
1. Timeline output blanking
Setting a blanking value using the Timeline > Output Blanking assigns a blanking/letterbox value to the entire timeline. This method is limited to a list of preset aspect ratios and can become unusable if the required value is not present in the available options. It can also become seriously limiting if the project requires different aspect ratios for different shots, scenes, or sections of the timeline.
2. Output Sizing
If the project requires a non-standard aspect ratio or multiple aspect ratios, the Output Sizing module can be used very effectively. With this feature, the Top, Right, Bottom, and Left pixel values can be adjusted to obtain any required aspect ratio value.
- A single aspect ratio can be set for the whole timeline with the Timeline option.
- Different shots, scenes, or sections of the timeline can be assigned different aspect ratio values using the Clip option.
The above settings will limit the analysis to the active image area and record the respective values as L5 metadata in the exported Dolby Vision metadata (XML) file.
L5 metadata records either symmetrical set horizontal or vertical blanking values.
Note: Although Blackmagic Resolve has been used to explain the various settings/configurations that have to be taken into consideration before creating Dolby Vision content, all content creation systems certified with Dolby Vision can be used in a similar fashion to create content, as long as the required parameters are set correctly.
See this article for Dolby Vision enabled color grading and packaging systems: https://professionalsupport.dolby.com/s/article/Dolby-Vision-compatible-Color-Grading-Packaging-Systems?language=en_US
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