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ACES Output Transforms VWG 

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Meeting #31, November 24th, 1pm PT


Alex Fry
Kevin Wheatley
Scott Dyer
Nick Shaw

Rémi Achard
Daniel Brylka
Sean Cooper
Michael De Caria
Zach Lewis
Joe McC
Michael Parsons
James Pickett
Joshua Pines
Matthias Scharfenberg
Daniele Siragusano
Shane Smith

Meeting Notes

  • Kevin Wheatley: The TAC meeting was last week, and we went over the spreadsheet of requirements. We need to categorize which can be met by our three candidates, and how much effort each might require, by the end of the year. We need to feed back to the TAC whether the minimal set of changes would achieve a reasonable proportion of the requirements, so they can consider how much to extend the original deadline. We also want to discuss the meeting cadence between now and the end of January – stay every two week, or maybe every week but perhaps shorter meetings.
  • Joshua Pines: Do people think the TAC's requests are reasonable?
  • Kevin Wheatley: One difficulty we have is availability of people to carry out work.
  • Nick Shaw: It's not too much of an assumption to say were sure we can't achieve all the requirements with a minor tweak to the current Output Transform, is it? Some definitely need a different approach. How do we define meeting is enough of them? Doug Walker's "T-shirt approach"?
  • Kevin Wheatley: The T-shirt sizing measure is about how big a talk something is and the amount of resources needed. But even if we had infinite resources, could a minimal set of tweaks satisfy enough of the requirements? We have three approaches on the table – Minimal tweaks to the current version; Jed's OpenDRT or something based on it; or something based on a CAM. The CAM requires the most work, but given that what Alex did was put together quite quickly, the results look pretty good. The point of the exercise is to see whether we could achieve a reasonable proportion of these requirements if we had a limited deadline imposed on us.
  • Scott Dyer: The original aggressive timeline was set outside our control. This is a very complex problem. And I think the TAC has realised the timeline is unrealistic, so they want to make the problem smaller in the short term. So initially it's an evaluation of if minimal changes is enough to become ACES 2.0. What requirements are showstoppers, so they could set a more realistic timeline. A target date for a release candidates for people to test (which they may not like). So we need to add three columns to the spreadsheet and evaluate each requirement against each candidate.
  • Joshua Pines: Each column would contain either "no" or small/medium/large for how much work it is.
  • Scott Dyer: Some things will require investigation to know how much work is needed.
  • Alex Fry: Tone scale defined for all float values shouldn't be controversial.
  • Nick Shaw: Likewise continuity, although there is obviously no continuous domain between e.g. NaN and infinity.
  • Kevin Wheatley: Perhaps infinity in would produce the same output as MAX_FLOAT in? I think monotonicity is also small.
  • Nick Shaw: Although it does depend on what we define as tone. Increasing luminance could be a decrease in a different "brightness" attribute along some gradients.
  • Alex Fry: I'd say Medium for ZCAM
  • Kevin Wheatley: Even for neutrals?
  • Joshua Pines: It's an under-defined requirement. Is it just luminance?
  • Scott Dyer: Originally the list said "neutral tone scale".
  • Kevin Wheatley: Non-asymptotic is easier with less roll-off, but that ties to less look and needing a default LMT (which nobody objected to last week). We can say medium in this first pass, and revisit it later.
  • Daniele Siragusano: Does tone scale mean for R=G=B?
  • Kevin Wheatley: I think it's some kind of cylinder around R=G=B that  we can consider neutral.
  • Nick Shaw: Is there a metric for a just noticeable difference from neutral?
  • Daniele Siragusano: We could define it backwards from the display referred ACES white point.
  • Kevin Wheatley: But there's some complexity from the fact we never settled on whether you fully adopt the white, or if there could be something else like a bias light in the environment. But for now let's say the colorimetry of the nominal equal value output.
  • Scott Dyer: I'd say neutral tone scale where R=G=B which would result in ACES white at output unless you add additional modifications.
  • Kevin Wheatley: Of course some of our current outputs adapt fully to the display white.