Scott Dyer: It's great to see many people who don't usually attend. We want toto plan our work towards an implementation of the group's algorithm that works for everybody's performance needs in a way that coordinates with what people may already have implemented, so it plays nicely moving forward. What are the needs? And what are the options to fulfill those. with minimal impact?
Nick Shaw: Before we start that I'll just mention, I found why my DCTL is not quite in sync with the CTL. I hadn't kept up with the change that was made to the CTL to vary lower hull gamma with peak luminance. I don't think the v60 Blink has that either, as my DCTL matches that. When I make the change it matches the CTL. I'll test more tomorrow then push the change.
Kevin Wheatley: That change is already in OCIO. We should fix the v60 Blink. What initial thoughts do implementers have? Shall we start with OCIO?
Carol Payne: We release an OCIO implementers' preview in OCIO 2.4.0 in October. There is still optimization to be done, but we wanted to get it out there. We had planned to do a full release in 2.4.1 this week, but there is still work to do. The ACES 2 config's won't be built in, but are available for download. We now plan a 2.4.2 release in early March. We would like to talk to other implementers about the optimizations we are considering, as we want the optimizations to be agreed on by this group.
Doug Walker: ACES 1 was a LUT implementation in OCIO. This caused issues especially for bright colors. In OCIOv2 we moved to a functional shader based implementation. We'd like to have the same for ACES 2.
Kevin Wheatley: Worth noting that OCIO has a GPU and CPU path.
Doug Walker: So ACES 2 is in 2.4.0 now, and we've done some speed tests on the CPU path and it's 3 to 8x slower than ACES 1, depending on hardware. GPU profiling is harder. The algorithm is more compute intensive than ACES 1, and there have been suggestions here about possible optimizations, and we've been exploring some in OCIO.
Scott Dyer: We know some optimizations may change pixel output. If we decide those are desirable, we want to do it once and in a way everybody agrees on. Those wouldn't change the look, but we would need to update the test images.
Kevin Wheatley: I was just clarifying in the chat that OCIO has split the configs into a D65 and ACES white'D60' config. We felt users would need one or the other. But configs with both can be made.
Daniele Siragusano: You want to not suggest D65 and D60 in a mixed environment, and have one or the other for both cinema and TV?
Kevin Wheatley: That was the feedback we had. In VFX you are using one or the other.
Carol Payne: This is OCIO specific. In finishing you might need both.
Doug Walker: The generator produces 3 configs – D65, D60 and one with everything. People can customize as they want.
Carol Payne: We want to make it clear so people don't get confused. SO we want sensible defaults, and encourage people to make a conscious choice.
Alex Fry: J asks if we should refer to it as ACES white rather than D60?
Nick Shaw: Might that make it sound as if it is the ACES default that people should use?"D60 sim" already confuses people.
J. Schulte: I'm calling a spade a spade. We here know the difference, but as we broaden the audience it's a good thing for people to call it the right thing.
Alex Fry: Does it need a better name?
Scott Dyer: In the documentation we refer to it as the ACES white point, and make clear that calling it D60 is shorthand. But it's a longer discussion, not for this meeting.
Daniele Siragusano: There are implications if you want to support it more generally.
Kevin Wheatley: Any other implementers have experiences they want to share?
Scott Dyer: Anybody else experience the speed issues OCIO mention.
Patrick Renner: We are currently baking LUTs, but we've noticed LUTs don't hold up so well for ACES 2, so we need to look at other options, one of which is OCIO. It feels the route we took was the right one, because otherwise we would be seeing the same issues OCIO is. So we are just observing for now.
Daniele Siragusano: We haven't started an implementation either, because ti is clear things will change. Rather than everyone doing different optimizations, it seems better if one party goes ahead and makes the obvious optimizations, and we follow. Or it will take another 100 meetings! OCIO is kind of the reference that's used in VFX, so it's more important for us to match that than the CTL.
ACES Output Transforms VWG
Meeting #174, December 11th, 1pm PT
[Meeting Recording]
Attendees
Meeting Notes