Thursday, May 7, 2020
5:00pm - 6:00pm PT (Los Angeles time / UTC-12:00am)
Please join us for the next meeting of this virtual working group (VWG). Future meeting dates for this month include:
5/14/20 9:30am
5/21/20 5pm
5/28/20 9:30am
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.
Please note that meetings are recorded and transcribed and open to the public. By participating you are agreeing to the ACESCentral Virtual Working Group Participation Guidelines
Audio Only
You can also dial in using your phone.
Dial the closest number to your location and then follow the prompts to enter the access code. United States: +1 (669) 224-3319 Access Code: 241-798-885
Note - there was a lot of all over the place discussion this meeting, if you want the real context, it would be a good one to listen to the recording.
@LarsB - exposure invariance only possible without limiting input/output - we need to make make clear we are talking about scene-referred in the Progress Report so display limits are not relevant
List things that are out of scope in Progress Report
Is exposure invariance truly necessary? Lars points out luminance might change - but for scene-referred, luminance can be negative and therefore not useful.
@joachim.zell brought up chromatic aberration - nice to have reference images here, but not really an issue for a gamut mapping algorithm
How do we deal with way out of gamut red but in gamut green? This is actually the most common problem. @carolalynn : this is where the safety gamut comes into play
How do we identify what is ‘right’ or ‘good’? Discussion around camera manufacturers color pipeline vs aces for visual reference
Lars - working on a 2020 to r709 mapping, cyan is the hardest. What are the hardest colors in ACES to map? Group responded with blues for sure.
@Troy_James_Sobotka proposed that a macbeth chart would be a good place to start for colors we care about? At least as a ground truth - macbeth colors should not ever be affected by our algorithm as a base level of acceptability. 190 or 24 chart?
What do we do with values outside of AP0? Do we clamp? Treat them as valid?
JZ - do we need a golden eye group? Present mapped images and see what people think - maybe eventually, after our own group has done visual/measurable testing
@Thomas_Mansencal raised a grading operator downstream of gamut mapping to ‘steer’ hues back on track. Matthias’ Nuke script has this option, but it’s global – introduces new artefacts when qualified. This is problematic for the zone of trust.
We need to remember that there will normally be grading as well. So if our gamut mapper ‘heals’ the image so it is easier for the colorist to get to where they want, that’s a big improvement on the current situation.
JzAzBz uses the Reinhart tonemapping equation:
Jz = ((1 + d) Iz)/(1 + d Iz) - d0
It can be applied to other single-channel remapping such as saturation.
It can be extended with a linear section at the bottom, for the “safe zone”
It can be set to map one range to another range.
It is trivially invertible.
