To the ODT Virtual Working Group,
The ACES leadership team would like to express our appreciation for your participation in the process of planning the future direction of ACES Output Transforms and for improving support of HDR workflows and displays. In particular, we’d like to that the chairs of the Virtual Working Group, Thad Beier and Bill Mandel, for their leadership of this work. While there is more investigative work to do, we feel enough consensus was reached to propose rolling out a useful collection of enhancements in the near term. The proposed enhancements will be released as part of a “point release” in the next couple of months.
In this point release, we propose to deliver a few often-requested Output Device Transforms. These ODTs include:
- SDR ODTs for P3 devices with a D65 calibration white point:
- SDR ODTs with P3 D65 and Rec.709 gamut limiting in a Rec.2020 container:
- HDR Output Transforms built with the proposed Single Stage Tone Scale algorithm and parameterized output model (more on this below) with presets for:
- Dolby Cinema Projector (P3D65_ST2084_108nits)
- Design, testing and recommended usage documentation
Through the discussions in the Virtual Working Group, it became clear that producing HDR Output Device Transforms using ACES 1.0’s discrete, two-stage tone scale is difficult, limiting and results in fairly inelegant math. To address these issues, an alternative Single Stage Tone Scale algorithm was proposed as a means to more directly generate output transform tone scales while preserving the important conceptual construct of the Reference Rendering Transform (RRT). We believe the Single Stage Tone Scale algorithm provides a simpler, more intuitive and mathematically elegant means of supporting devices with a wide variety of dynamic ranges while conforming to core ACES design principles.
This point release will also introduce additional improvements to the HDR ODTs such as a unified parametric output transform model that substantially improves algorithmic consistency. On a historical note, the HDR ODTs included with the ACES 1.0 release were created prior to the general availability of professional HDR mastering displays. Therefore, these ODTs have been subject to an enhanced level of scrutiny under production conditions since ACES 1.0 was released. Based on the feedback received and the Virtual Working Group discussions, there are clearly improvements that can and should be made now. Given the preliminary nature of the ACES 1.0 HDR ODTs, we feel that it’s reasonable to replace those transforms, as well as add newly-requested HDR transforms, with the new-and-improved HDR ODTs that implement the unified parametric output transform model along with the Single Stage Tone Scale. In order to minimize market disruption and equipment manufacturer impact, the parameters will not be exposed to end-users at this time. Once the field performance of the new ODT model is verified, it will be considered for SDR transforms and for end-user parameter setting. And as always, the original v1.0 HDR ODTs will always be available on github for shows that used them.
We invite you to post your thoughts on the proposed rollout, the included features, and the release timeframe within the next 7 days. Again, we appreciate your contributions and look forward to your continued collaboration.