Opacity rendered differently over transparency than over solid colours

[RobBarrett]

I'm posting this as a bug, but please change it to a Discussion if this is intended behaviour.

I've noticed that when animating the opacity of a layer, the apparent level of opacity is rendered differently against an actual background colour compared to against a transparent background with the comp's BG set to that same colour.

I'm not sure that's explained clearly, but I think the attached video demonstrates this better.

I could imagine that there are proper technical reasons for this difference, but without this knowledge, it feels unexpected that these render differently.

[David.Arbor]

Hey @RobBarrett!

I tried to reproduce your issue and wasn't able to (i.e. the examples faded identically), so it made me think this was a color management or gamma thing.

Sure enough, I can reproduce your issue if the "Blend colors using 1.0 gamma" box is checked. Is that the case for you? If so, then this would be expected behavior, and turning the box off to blend values using a 2.2 gamma should produce visually identical results.

Thanks,
- David, After Effects Engineering Team

[RobBarrett]

Thanks, that makes sense, and I'm seeing the same here. I changed that setting a couple of weeks ago, when we were talking on Slack about the new Unmult effect, and forgot to reset it! Just to confirm, is the default setting for this to be unchecked?

[David.Arbor]

Ah, that's right. Yeah, enabling it definitely makes your composites with Unmult look better.
But yes, the default is unchecked.

- David, After Effects Engineering Team