Notice of Meeting - ACES Gamut Mapping VWG - Meeting #36 - 12/3/2020

ACES Gamut Mapping VWG Meeting #36

Thursday, December 3, 2020
9:30am - 10:30am Pacific Time (UTC-5:30pm)

Please join us for the next meeting of this virtual working group (VWG). Future meeting dates for this month include:

  • 12/10
  • 12/17 (TBD?)

Dropbox Paper link for this group:

We will be using the same GoToMeeting url and phone numbers as in previous groups.
You may join via computer/smartphone (preferred) which will allow you to see any presentations or documents that are shared or you can join using a telephone which will be an audio only experience.

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Things to watch out for:

  • PR with usage comments for the CTL
  • Decision around the power compression setting
  • Documentation Deliverable for comments


  • Should we have a separate CTL for inverse?
    • Most CTL is this way
    • But it would increase duplication of code, and also possibly encourage the use?
    • Group decided to keep it a single file with parameter for inverse
  • Is the power setting of 1.2 our true default?
    • When we’re talking about HDR, should our default be higher? Feedback was that in SDR, hard to tell the difference between the power settings, but in HDR, much more obvious.
    • Should the default be the highest option at 1.3 to maintain the most saturation?
  • Should we add a comment in the CTL to note that the algorithm should be used directly after the IDT, before any other work?
    • Group consensus is yes, we are fine to add comments in the CTL
    • It’s not an official standard, we can put ideal usage in the code
    • If the CTL is the only thing someone sees, it should be explicit
  • Should it even be called an LMT (LMT appears in the TransformID)?
    • @hbrendel - people will use it where they feel like it’s needed, we should account for that
    • But in VFX, should be earlier in the chain and then work is done
    • What would we call it instead?
    • @matthias.scharfenber : not sure we should invent a new term, it still fits most of the characteristics of an LMT
    • Definition of an LMT: “User determined creative transform”, last thing before the RRT in all block diagrams
    • @Alexander_Forsythe : does it fit into the pre-grade box? But that doesn’t have an official name
    • @joseph : we never anticipated pre-grade being CTL, so there is no technical category for it
    • @Giardiello : should we call it a CSC (Color Space Conversion)?
    • @carolalynn / @matthias.scharfenber : the encoding and primaries are not changing - the scene values are just “moving”
    • @KevinJW : what about Scene Modification Transform? SMT already exists.
    • @joseph : we can always revisit this down the road, as we look into updates to transform IDs, etc.
  • @Thomas_Mansencal : should talk about handing over code to the Academy
    • @sdyer : there is precedent from earlier groups to have other repos on the aces dev github, we should be able to move things over, just figuring out how to segment the work
    • Might be moving to ReadTheDocs for documentation, so aren’t going to worry about format of documentation deliverable for now.

Recording and Transcript