This article provides some basic information about HDR10 static metadata and how users can calculate and provide these values in Dolby Vision metadata.

 

The following topics are covered:
 

• MaxFALL/MaxCLL definition
• MaxFALL/MaxCLL calculation
• Examples using CM_analyze
• MaxFALL and MaxCLL insertion to a Dolby Vision XML 

Static Metadata

MaxFALL/MaxCLL is static metadata required for HDR10 content. 

MaxFALL (Maximum Frame Average Light Level) indicates the maximum value of the frame average light level (in cd/m2 or nits) of the entire playback sequence. MaxFALL is calculated by averaging the decoded luminance values of all the pixels within a frame. MaxFALL is usually much lower than MaxCLL.

MaxCLL (Maximum Content Light Level) indicates the maximum light level of any single pixel (in cd/m2 or nits) of the entire playback sequence. MaxCLL is usually measured off the final delivered content after mastering. If one uses the full light level of the HDR mastering display and adds a hard clip at its maximum value, MaxCLL would be equal to the peak luminance of the mastering monitor.

 

MaxCLL/MaxFALL together forms static metadata as it uses the same values for the entire program, while Dolby Vision dynamic metadata changes on a shot by shot (or when required, frame by frame) basis.

Both HDR10 and Dolby Vision are based on the ST.2084 (PQ) EOTF.

Different consumer HDR displays have different peak luminance and contrast capabilities, and more often than not, these fall below the capabilities of the mastering monitors used in professional post production. Therefore in most cases, PQ encoded images will have to be scaled or mapped to match the capabilities of the target consumer display device. This scaling or mapping is controlled and managed by metadata.

 

MaxFALL/MaxCLL calculation 

MaxFALL/MaxCLL metadata is not required for a Dolby Vision deliverable, nevertheless, Dolby supports the effort to supply correct metadata to produce better end user entertainment experience. Therefore, HDR10 static metadata values can be stored inside Dolby Vision metadata as L6. MaxFALL/MaxCLL are not calculated as part of the Dolby Vision metadata creation process. They require a separate analysis that can be performed on systems like Colorfront Transkoder, MTI Cortex, etc. Some systems write L6 metadata during the export process of a Dolby Vision IMF package.

Alternatively, MaxFALL/MaxCLL metadata can be calculated using Dolby's cm_analyze which is included in the Dolby Vision Professional Tools suite. Once these values are calculated, they can be added to an existing Dolby Vision XML as Level6 (L6) metadata so as to deliver both Dolby Vision as well as HDR10 metadata in a single metadata asset.

Calculating MaxFALL/MaxCLL using Cm_analyze

Cm_analyze can be used to calculate HDR10 static metadata by using the "--bda" argument followed by the source format specification "--source-format <arg>" of the content and the aspect ratios "--aspect-ratios <arg1> <arg2>".

./cm_analyze –-bda –-source-format <arg> --aspect-ratios <arg1> <arg2> <input_image_sequence_########.tif> <output.xml>

The < > signs solely serve as a placeholder and must not be used in the final command! Arg must be populated with the respective arguments. For a comprehensive list of arguments, see the Dolby Vision Professional User Manual.

CM_analyze computes MaxFALL, MaxCLL as per the blu-ray spec document. Other tools like Colorfront Transkoder or MTI Cortex may deliver different results due to the respective algorithms that they use.

 

Examples:

ProRes 4444XQ - ST.2084(PQ) Rec.2020 source, canvas aspect ratio 1:1.777778, image aspect ratio 1:2.0

./cm_analyze –-bda –-source-format "bt2020 pq" --aspect-ratios 1.777778 2.0 testfolder/input.mov testfolder/output.xml>

 

ProRes 4444XQ - ST.2084(PQ) Rec.2020 source, canvas aspect ratio 1:1.777778, image aspect ratio 1:2.0

./cm_analyze –-bda –-source-format "bt2020 pq" --aspect-ratios 1.777778 2.0 testfolder/input.mov testfolder/output.xml>


 

  

MaxFALL and MaxCLL insertion to a Dolby Vision XML 

Once the MaxFALL/MaxCLL values are calculated using Cm_analyze, they can be inserted in the L6 placeholder within an existing Dolby Vision XML using Metafier.

To insert these values as Level 6 metadata use the "-- max-fall-cll" command.
 

./metafier --max-fall-cll <arg1> <arg2> <metadata.xml>

 

For more info on how to use cm_analyze and metafier, refer to the Dolby Vision Professional User Manual .