Notice of Meeting - ACES Gamut Mapping VWG - Meeting #35 - 11/19/2020

Discussions - ACESNext VWG – Gamut Compression/Mapping
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ACES Gamut Mapping VWG Meeting #35

Thursday, November 19, 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:

  • TBD

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Recap:

  • @nick has a first version of the CTL deliverable, PR here for comment.
  • Talked a bit more through the despill issue brought up by a tester from MPC, all agreed that the benefit for compositors is being to apply at will - upstream and downstream operations will be necessary
  • Documentation:
    • Technical doc - specs, math, how it works
    • User documentation - examples, use cases, things to watch out for
    • @joachim.zell: it should be intuitive, easy to understand, pave our own path so to speak. Should find a guinea pig not familiar to read through the docs.
    • @sdyer : quick 1 min videos would be really useful. But for now, focus on design decisions and outcomes.
  • How do we “archive” the work of the group - github repo, working docs, research, etc
  • It was generally agreed that wider “open” testing would not give useful feedback
  • Implementation group: looking for participants from software vendors, etc, as well as soliciting volunteers for leaders :wink:

Recording and Transcript

1 Like
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Hi,
Sorry I could not attend the last meetings.

Just wanted to throw two things:
1)

You do a very great job on this, I can only applaud to all of you.

  1. Regarding Despill:

A tri-component camera follows the same physical rules in terms of colour mixing as the human observer, this means all Grassman’s laws are true for a camera as well, as long as we only use 3x3 matrices in the camera processing.

For our case here it means a mixture of two colours will always be on a straight line between the two colours (on a chromaticity plane). It cannot be somewhere else. So if we have a green background and brown (yellow) hair, all motion-blurred pixels lie exactly on a line (in chromaticity plane) connecting the hair and the green background.
If we apply a non-linear transformation to the image (like the compress Gamut) we destroy this behaviour. Therefore it is expected that things which rely on linearity will not work so great with gamut compressed images, and hence it is a good choice to have gamut compression as an optional component.

This is one of the major reasons I also strongly dislike the idea of more complex IDTs backed into the footage, it would produce unideal images for VFX and other processes which rely on Grassman’s laws.

6 Likes
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Said it already but repeating again: Good job team! :slight_smile:

1 Like