“HDR grades which offer little, to no benefit over SDR, will be rejected”

The following excerpts are from Technical Specification for the Delivery of Content Sky UK, the UK’s largest pay-TV broadcaster.

Primary Image-Acquisition

To ensure viewers observe a noticeable improvement in resolution between the different definition tiers (e.g., HD and UHD) as well as SDR and HDR, the minimum camera requirements in Table 1 must be met for the commission type and format. 

Colour Bit Depth

16-bit capture is encouraged for higher-end Scripted Production.

• To limit visible banding, Productions which will require significant changes to luminance or colour saturation, either due to stylistic choice or due to the challenging nature of a production which may hinder consistently accurate exposure, must capture at a greater bit-depth than what is listed in Table 1.

Dynamic Range

Whilst there are various methods to measure dynamic range, the stops of dynamic range listed in Table 1 are included for guidance.

Post-Production Visual Pipeline

Scripted Productions:

A ≥ 12-bit colour depth must be maintained from the camera to the grade.

High Dynamic Range

• The HDR version should be graded using the PQ EOTF. Approval is required to use the HLG EOTF.
• The HDR content must be delivered to Sky in the same HDR format in which it was graded. It is not acceptable to convert from one HDR format to another between the grade and delivery.
• The grades must look stylistically similar across the SDR and HDR formats, particularly with regards to midtones.
• HDR grades must offer a perceptual increase in dynamic range over SDR. Transient overshoots that exceed SDR levels, which are detectable on equipment but barely perceivable to viewers, do not qualify.
• Where appropriate, the HDR grade should utilise the wider colour gamut available, with chromaticity that exceeds what is available in BT.709.

Speak to your Sky contact ahead of being commissioned if the intended look will not utilise HDR’s increased dynamic range, as an additional HDR grade may not be required. HDR grades which offer little, to no benefit over SDR, will be rejected.

Where the creative intent results in a single episode that does not exhibit the benefits HDR offers, when the rest of the series does (e.g., a flashback episode with a muted grade), Sky should be informed ahead of delivery to avoid incorrect rejection of the individual episode.

The term HDR10 is not used in this document. HDR10 is a consumer format that is explicitly 10-bit, whilst deliverables sent to Sky can have a greater bit-depth. HDR10 is also often understood to have a chroma sub- sampling of 4:2:0, which is not acceptable for deliverables sent to Sky. The terms PQ (Perceptual Quantization) and HLG (Hybrid Log-Gamma), as defined in BT.2100, are used to denote the specific HDR formats which Sky can accept.

Additional HDR Information

HDR Grading Guidance

Consideration must be given to providing the optimum HDR image. To avoid an overly reserved approach to what HDR offers, the initial grade should be completed on the HDR version, with the SDR grade being completed afterwards. The full luminance range of the HDR grading monitor may be used.