The ATSC “System Standard” (Document A/300) is the central guiding document in the ATSC 3.0 suite of standards. Updated annually, it details the most recent versions of the ATSC 3.0 standards in force for that year and provides general informative guidance about the standards. The latest version, ATSC A/300:2022-04 “System Standard,” passed the ATSC membership ballot on April 8 and has now been published on the ATSC website.
One of the informative portions of A/300 modified in its newest version is the section on High Dynamic Range (HDR) video. Several HDR technologies are documented in the ATSC 3.0 Standard on Video (Document A/341. Until the current version, the only guidance the System Standard had about selecting a particular HDR system was in section 5.1.14:
“All ATSC 3.0 terrestrial and hybrid television services emitted within a given region should use one High Dynamic Range (HDR) system selected for that region from those defined in A/341.”
The newest version of A/300 now provides more HDR information and guidance:
“All ATSC 3.0 terrestrial and hybrid television services emitted within a given region should use one High Dynamic Range (HDR) system selected for that region from those defined in A/341 (i.e., PQ or HLG). Emission of SL-HDR1 derived from a PQ source is considered to be based on an underlying PQ transfer function. The North American Broadcasters Association (NABA) has recommended : “That systems based on an underlying PQ-based HDR transfer function (SMPTE ST 2084) with optional static (SMPTE ST 2086) and/or dynamic metadata (SMPTE ST 2094) be used for ATSC 3.0 program emission in North America.2
Footnote 2: This is a non-binding recommendation from a trade association.”
Reference 47 in the above paragraph is listed in the Informative References (Section 2.2) and refers to the North American Broadcasters Association (NABA) HDR Emission Format Recommendation, issued in August 2021. NABA is a trade association dealing with technical, operational, and regulatory issues affecting North American broadcasters headquartered in Toronto, Canada. In early 2021 NABA formed an HDR Study Group (chaired by NAB’s Senior Vice President, Technology, Lynn Claudy) to survey and discuss the current and likely future state of the multi-industry landscape on HDR technologies.
It was clear to the group that multiple HDR systems would co-exist, and conversions will be performed. However, any conversion adds complexity and is imperfect. “Round-trip” conversions, where system A is converted to system B and then back to system A, should particularly be avoided, and “round-trip” plus additional conversions may reduce quality and introduce color shifts. The group noted that while content can go through a conversion reasonably well under certain circumstances, the typical end result is likely to exhibit the worst aspects of each system – conversion never makes things better.
The study group ultimately reached a consensus on a preferred approach, which was then refined by NABA’s Technical Committee and its Board of Directors and released at the beginning of August 2021. The full Recommendation is shown below. More information on the rationale for the Recommendation can be found on the NABA website.
It is important to note that this is a recommendation on emission only, and it does not address HDR in production. It is also only a recommendation, meaning it is not a requirement. As one can likely tell by the process followed, this subject was given heavy consideration by NABA and the ATSC, and I believe it is likely to be followed. HDR is a significant benefit of adopting Ultra HD, and this recommendation on emission is expected to aid in the deployment of Ultra HD in the years ahead.