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ACES Output Transforms VWG 

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Meeting #119, September 20th, 1pm PT


Kevin Wheatley
Scott Dyer
Nick Shaw

Daniel Brylka
Christopher Jerome
Jeffrey D Mathias
Willem Nagtglas
Pekka Riikonen
Daniele Siragusano
Christian Wieberg-Nielsen

Meeting Notes

  • Kevin Wheatley: Luke and Alex apologize for their absence. Alex published the combination of his an Pekka's work. Jeffrey posted about seeing some NaNs, but Alex did do this in a rush. 
  • Pekka Riikonen: I think NaNs come from compress mode.
  • Kevin Wheatley: We need to trace values through to find the source of NaNs.
  • Pekka Riikonen: The quadratic in the gamut mapper can also produce NaNs.
  • Kevin Wheatley: We could look at other quadratic formulae. Or are there no roots there.
  • Pekka Riikonen: Limiting M makes NaNs go away.
  • Nick Shaw: The quadratic solve finds the angle for the compression vector which hits the J axis at a particular point. But outside the intended range there may be no solution which intersects at the right point.
  • Kevin Wheatley: Did anybody look at v44 and 44b?
  • Scott Dyer: I had a look. But didn't have a chance to do side by side with HDR. I saw some NaN/LUT artifacts, which I'm sure we can fix.
  • Kevin Wheatley: Our experiments are to match HDR and SDR and 709 and P3. Then we look at the problematic images, and check they are better than before.
  • Christopher Jerome: I think the ARRI bar image where P3 clipped before 709, it's now about equal.
  • Kevin Wheatley: Hopefully in the coming weeks we can kill the obvious bugs, then noodle with parameters to help with any discrepancies. It would be helpful if people can comment on problem images in the DRT thread on ACES Central.
  • Christopher Jerome: Added control over when something hits the boundary and at what angle would help.
  • Kevin Wheatley: Any tests people think should be done that they can't do themselves.
  • Pekka Riikonen: HDR SDR comparison. I will push some small tweaks I've made to parameters and algorithms in v44.
  • DS: Should 44 and 44b reach the mastering space bounds? They struggle to hit the red corner. Are we still wanting to hit the corners?
  • Pekka Riikonen: Hit or get very close. 44 expands colorfulness more, where the previous version maybe went over. In 44b the locus reach mode compresses more.
[Daniele showed in Baselight that it wasn't hitting the Rec.709 red corner]
  • Nick Shaw: I could be the LUT shaper is limiting it. That is the same one we've always used, and the DRT has changed.
  • Kevin Wheatley: We want to hit 709 and P3 would be nice. We controls, particularly in the gamut mapping that may help.
  • Nick Shaw: One thing is saw in the new Resolve 18.6 is custom DCTL ODTs can be tagged with their color space, for OS color management and metadata. At IBC I mentioned we were using Blink not DCTL for prototyping, because Blink offers an init() function where DCTL runs everything per pixel. Nothing was promised, but I was told adding an init() to DCTL was not impossible. Maybe if we show them our use case example.
[Pekka showed a 3D JMh plot of v44b]
  • Pekka Riikonen: It doesn't hit the red corner in the Blink either. This is locus reach. AP1 reach is better. It's still missing a bit along the cyan edge.
  • Kevin Wheatley: That makes sense given display encodings cut a lot of the green to blue area off.

Meeting #118, September 13th, 1pm PT


Alex Fry
Kevin Wheatley