How do you accurately key in Log space inside Resolve?

[Thomas d'Auteuil]

I've seen the episode "Piping a key downstream" in the first color grading course. It makes sense to CST into rec709 to have a more accurate contrast and saturation to key in. However, it's a hassle to send keys to other nodes and potentially risking to break the node structure (I use ripple node changes on big projects).

Is there a way to have a "Log Space Aware" HSL qualifier? What's the best procedure to have accurate keys?

My goal is to have my keying done as cleanly as possible and changing the exposure of that key in log space (ex: bringing up the exposure in the skin).

[Abby Bader]

Most of the times you can key in log without any problem, but different algorithms works for you on different methods.

[Thomas d'Auteuil]

15 hours ago, Abby Bader said:

Most of the times you can key in log without any problem

Usually, it's feasible, but the luma and saturation controls are all crammed up in a tiny zone. It's overly sensitive and imprecise. More often than not, keys are much cleaner (and easier) in rec709. That's why I'm wondering if I'm doing something wrong, like not using the right qualifying tool.

[Rune Felix Holm]

A colorspace aware qualifier would be the best solution. It would make sense to suggest it to BMD on the BMD forum.

As far as I know there is no simple solution other that keying in the timeline colorspace via a cst node.

[Stefan Stark]

I usually have a key piping structure with a CST and a couple of parallel nodes present in a fixed node structures across all clips.

… or you could work in Color Managed Color Science 

But yeah, a color space aware picker would indeed be awsome.

[Thomas d'Auteuil]

@Stefan Stark I totally agree. I tried using the key piping method, but it became too cumbersome on large projects. Instead, I simply got used to be ultraprecise in the luma and saturation selection.

I'll try messaging the people at Blackmagic to suggest a color space aware picker tool.

@Rune Felix Holm For now, I'm strongly considering converting my footage to rec709 in the middle of my node tree. I just don't know anything about how to grade in rec709 without messing up the gamma and introducing ugly tints.

Edited October 21, 2021 by Thomas d'Auteuil

[Rune Felix Holm]

Pipe the mask output from the rec 709 node to your log nodes to stay in log all the way to the lut.

Stefans image shows how to set this up. All that is missing is to connect the key matte output to the log grading nodes.

[Luca Di Gioacchino]

All you're doing by keying is creating a matte which can then be used to perform targeted corrections in whatever color space you wish to work in, so what does it matter if you create that matte in Rec 709? 

 

[Rune Felix Holm]

When you key in rec709 color space keying becomes a lot easier and more precise in a rec 709 project as mentioned in the original post from Thomas.

[Luca Di Gioacchino]

Yes, I know that keying in Rec709 is easier.

[Rune Felix Holm]

Then I don't understand your question. Is there a better way to key log material?

[Luca Di Gioacchino]

No, not really, which is why I said create the matte in Rec 709, then import it and use it a log color space, if that's what you wish to do.