Mastering: HDR masters, SDR derivations and Dolby Vision metadata

Mastering is the stage at which the graded picture becomes a set of definitive files: the HDR master, the SDR version and the metadata that tells displays how to show them. CINE-310 covered the craft of grading in HDR and making SDR trims. This lesson looks at the technical side of the same work: how the HDR master is defined, how SDR versions are derived, how Dolby Vision analysis and trim metadata work, how MaxCLL and MaxFALL are measured and what the cinematographer should check before approving the master. The values below are common examples from public guidelines; the current specification for your production always takes precedence.

What makes a master

A master is the highest-quality finished version of the picture from which all other versions are made. For a premium HDR streaming title, the master is typically:

• Graded on a reference display, often a 1,000-nit P3-D65 PQ display, in a controlled grading suite.
• Rendered at the delivery resolution, usually 3,840 × 2,160, at the project frame rate, from the conformed timeline with final VFX.
• Stored as high-bit-depth image files, such as 16-bit TIFF or OpenEXR sequences, or as lossless or high-quality compressed files, depending on the service.
• Accompanied by metadata describing the mastering display, MaxCLL, MaxFALL and, often, Dolby Vision dynamic metadata.
• Paired with an SDR version, either derived through metadata or rendered separately.

Netflix's public Dolby Vision mastering guidelines, for example, have described a workflow in which the HDR master is graded on a P3-D65 PQ display of at least 1,000 nits and Dolby Vision metadata is generated for the SDR and other target displays. Other services use similar approaches.

HDR-first and SDR-first workflows

There are two broad ways to build an HDR and SDR pair.

• HDR first: the colourist grades the HDR master, then makes SDR trims, often using Dolby Vision tools to derive an SDR version automatically and then adjust it. This is the usual approach for premium streaming originals.
• SDR first: the colourist grades SDR, then creates an HDR version, sometimes by expanding the SDR grade. This is less common for new streaming originals but may appear on mixed or legacy projects.

HDR-first workflows keep the most information in the master. The risk is that SDR becomes an afterthought; the cinematographer should insist on a proper SDR review, because many viewers will see that version.

Dolby Vision analysis and trims

Dolby Vision adds dynamic metadata to a PQ master. The process usually runs like this:

• Analysis: software measures each shot and records its minimum, average and maximum brightness. In Dolby Vision terms, these measurements are called Level 1 (L1) metadata.
• Trims: the colourist reviews the automatically mapped version for a target display, typically a 100-nit SDR Rec. 709 display, and adjusts parameters such as lift, gamma, gain, saturation and chroma for each shot. These adjustments are stored as trim metadata. Older metadata versions call them Level 2 (L2); the current version 4.0 metadata uses Level 8 (L8) trims, which allow trims for more target displays and add more controls.
• Other levels: Level 5 (L5) records the active picture area, such as letterbox bars; Level 6 (L6) records static values such as MaxCLL and MaxFALL for HDR10 compatibility; other levels describe the mastering display and content type.
• Output: the master files plus a metadata file, often an XML file, that is delivered with the picture or embedded in an IMF package.

A Dolby Vision television reads the metadata and maps each shot to its own capability, using the trims as guidance. The SDR version can be rendered from the same master and metadata.

Measuring MaxCLL and MaxFALL

MaxCLL and MaxFALL are calculated from the finished master, not guessed. For each frame, software converts every pixel to luminance in nits, using the maximum of the red, green and blue components as defined in CTA-861.3. It records the brightest pixel and the average of all pixels in the frame. MaxCLL is the highest brightest-pixel value across the programme; MaxFALL is the highest frame average.

Common mastering limits

Services often set limits or expectations for mastered values. Examples include:

• Peak luminance within the mastering display's range: no pixel above the reference display's peak, such as 1,000 nits, because nobody saw it.
• Colours within the mastering gamut: no colours outside P3-D65 when the master is graded on a P3 display.
• Reasonable MaxFALL: very high frame averages may be uncomfortable for viewers and may cause televisions to dim the picture to protect their panels.
• Accurate metadata: MaxCLL and MaxFALL values that match the content, not defaults copied from a template.
• Legal or full range as specified, with no unexpected clipping at the top or bottom of the signal.

These are checked in QC (Lesson 9). The cinematographer can help by keeping practical lights, windows and specular highlights within the mastering range in the grade, and by asking the colourist to use soft clips or roll-offs rather than hard clipping.

The SDR version

The SDR version is usually SDR Rec. 709 (BT.1886 display gamma, about 100 nits reference), delivered as a separate file or derived from Dolby Vision metadata. Even when derived automatically, it needs review.

• Check that skin tones, key colours and important dark details are preserved.
• Watch for highlights that look clipped or flat, and saturated lights that shift hue.
• Confirm that captions and graphics fit and that letterboxing is correct.
• Review on a calibrated SDR display at the reference brightness.

Some services ask for SDR versions in other forms, such as an SDR P3 version for theatrical use or an SDR Rec. 709 file for archive and broadcast partners. The deliverables list will say which.

Other derived versions

From one HDR master and metadata, finishing teams may produce:

• HDR10: PQ video with static metadata, derived from the Dolby Vision master.
• HDR10+: where requested, with its own dynamic metadata generated by analysis.
• HLG: for broadcast partners, by converting the PQ master to HLG with a standard transform.
• Theatrical versions: P3 DCI or P3-D65 versions for cinema screenings, often at 48 nits for SDR cinema.
• Lower-resolution versions: HD files for partners who need them, usually created from the 4K master.

Each derived version should be checked; conversions can change contrast, colour or highlights in unexpected ways.

What the cinematographer should check before approval

Before signing off, the cinematographer should review:

• The HDR master on the reference display, at least key scenes and any shots with practical lights, windows, sun or fire.
• The SDR version on a calibrated SDR display.
• A sample of shots on a consumer HDR television, in a calibrated or neutral mode, to see how tone mapping affects the look.
• MaxCLL, MaxFALL and gamut reports, to catch values outside the mastering range.
• The active picture area and letterboxing, especially for 2.39:1 or 2.00:1 frames in a 16:9 container.

Write down the review notes and any changes agreed. If the cinematographer cannot attend the final mastering, agree in advance on remote review links with calibrated displays, and identify a trusted colourist or post supervisor who can make final calls.