CST explicit output gamma Intermediate vs Use timeline

Hi all!
I'm trying to rationally learn some fundamentals of Color Grading in Resolve, v18.1.
One thing I can't manage to justify and led me to reach you out here (I'm afraid I'm a person who can't get pass an unanswered "why" ) is the following:

I have a project set as:

• Color Science: DaVinci YRGB
• Timeline color space: DWG/Intermediate
• Output color space: Rec.709/2.4

I import a scene shot in S-log3.Cine/S-log3.
In the color tab and I add a node, apply a CST and try two scenarios. In both I set Input Color Space and Gamma to S-Log3.Cine/S-Log3.

• In the first scenario I set Output Color Space to DWG and Output Gamma to "Use timeline" (which should be DWG Intermediate, right?).
• In the second I set Output Color Space to DWG and Output Gamma to DaVinci Intermediate

Result, the preview changes quite dramatically.
I wonder why should that be? I would intuitively expect no change whatsoever.

Thank you!

I too have noticed this and am wondering why

I wonder this as well.

Have you checked it hasn't automatically selected one of the "Apply * OOTF" settings?

Probably experiencing what RikshaDriver said. Apply Forward OOTF flipping on is perhaps a 'bug' left by the mechanism from a time before Timeline and Output space were able to be separate things in YRGB and a display space was always expected to be selected.

So how exactly correct in/out CST node settings should look like when one uses 'use timeline' vs. 'use XYZ' if, for example, timeline is DWGI and input/output are Rec709?

If you’re making a CST node sandwich Resolve will add the OOTF to the DWGI and not Timeline when going to 709/2.4, so it’s at least consistent, the result is nearly identical, but the logic is questionable.

Good Luck

If you’re making a CST node sandwich Resolve will add the OOTF to the DWGI and not Timeline when going to 709/2.4, so it’s at least consistent, the result is nearly identical, but the logic is questionable.

I'm sorry but I don't know how to interpret "so it’s at least consistent, the result is nearly identical, but the logic is questionable". We are just trying to find out simple straight answer to what is, I thought, simple straight question what should one use for node sandwich, 'use timeline' or 'use DWGI', and with which settings.

Use DWGI. DWGI isn't a display referred space. When the sandwich uses timeline it inserts the OOTF in the first node (Slog-DWGI) when it should be applied in the second (DWGI-Rec709/2.4). There might be underlying logic or it might be a bug. Either way there is no difference between timeline and DWGI if the OOTF is the same for both.

Good Luck

When the sandwich uses timeline it inserts the OOTF in the first node (Slog-DWGI) when it should be applied in the second (DWGI-Rec709/2.4).

I’m still trying to figure out what exactly I am told I should use. So please let me rephrase my question and illustrate it with screenshots:

I have, say, SGamut3.Cinema+SLog3 footage, I want to grade it on DWGI timeline so I can use color space aware tools, and my output is for YouTube that is expecting Rec709 (Scene). My color management project settings are:

Color science = DaVinci YRGB
Timeline color space = DWGI
Output color space = Rec709 (Scene)

Is everything correct so far?

Next I have node tree. First node is CST with settings in first screenshot. Last node is CST with settings in second screenshot. Are OOTF settings in them correct, please?

CST1.JPG (89.43 KiB) Viewed 1899 times

CST2.JPG (86.3 KiB) Viewed 1899 times

The forward OOTF should only be used when going from scene-referred to display-referred. The inverse only when going from display-referred to scene-referred (Not to be confused with Rec.709(scene)).

So Camera log -> DWGI = no OOTF, both are scene-referred color spaces
DWGI to Rec.709 Gamma 2.4 forward OOTF, as we are going to an SDR display

When you choose Rec.709 also as Gamma which is technically the same as Gamma 2.4, the OOTF is already included and thus doesn't need to be checked separately. It automatically switches on or off depending on which of the 2 gamma options you pick though.

You can also choose to go to timeline instead of DWGI from the camera, this will turn the forward OOTF on, but as explained earlier this seems to be a bug and should manually be turned off again. Going from camera to timeline and from timeline to Rec.709 allows you to globally change your working space without swapping it on all the CSTs. Interesting for doing tests to see how working in various working spaces is for grading with non colorspace aware tools but not recommendable swapping after the fact on actual work.

I think the fact that in theory, if your timeline is set to DaVinci Wide Gamut & DaVinci Intermediate in settings as your Timeline Color Space and you set the Output nodes to DaVinci Wide Gamut, both Timeline and DaVinci Wide Gamut should produce the same result.

When you choose Rec.709 also as Gamma which is technically the same as Gamma 2.4, the OOTF is already included and thus doesn't need to be checked separately. It automatically switches on or off depending on which of the 2 gamma options you pick though.

It is obvious to me I am extremely likely to make mistakes if I try to set OOTF’s manually. Would you say I can trust Resolve to set them automatically correct for me as long as I don’t state ‘use timeline’ but particular color space/gamma?

When you choose Rec.709 also as Gamma which is technically the same as Gamma 2.4 …

You just shattered one of my biggest assumptions and made my head spin and hurt. Rather than taking this thread in off-topic direction I will create new one for that and will, if you don’t mind, send you the link to it.

Thank you again!

Would you say I can trust Resolve to set them automatically correct for me as long as I don’t state ‘use timeline’ but particular color space/gamma?

In theory yes, but never hurts to double check!