Keying issues -> my first foray into colour mgmt 😫

[Unclextacy]

Hi guys, getting some shitty edges as soon as I comp some well-shot green screen over a purple background, and I suspect I’ve stuffed up my colour settings.
Forgive me, I’m a total colour n00b.

So I’ve started a project in 2026.2.2, and selected Aces 2.0 as my default project setting. First mistake, but I really need to learn this stuff so why the hell not.
My footage is 6k Sony Venice, and inside Action it inherits the SLog 3 Venice-S-Gamut3.cine LUT.
My viewer is ACES SDR 100 nits by default. I’ve got a purple gradient in the BG managed to the Venice LUT so they match. Trouble is - I’m getting a horrid pink edge around my key. Why is that and how do I fix it?

Thanks!

despilled fill:

result (with some grading via image node/CW etc):

[Ryland]

@Unclextacy

I’ve got a purple gradient in the BG managed to the Venice LUT so they match.

Can you explain this part a bit more? What is the source colorspace of the purple gradient? What transform are you using to push it to sLog?

[Unclextacy]

Thanks Ryland, I changed it in the Gradient node prefs menu.

[Unclextacy]

Actually Ryland - your question made me think that was the problem, and so I set the CM inside the menu to ‘from source’ and then did the conversion inside a CM node instead, and it’s fixed! Thankyou! Why did it do that though?

[Ryland]

Not super familiar with the gradient node. I just played around with it for a few minutes to try and make a purple gradient and I pretty quickly got myself into a place where the values were exceeding one. Log values over one generally don’t play nice. Probably something to do with that, but since I rarely comp in Log, use the color picker for creating colors, or use gradient, I’m not really sure.

[Ryland]

I never really stopped to think about it before, but I guess color source and gradient don’t really have a colorspace? They’re just raw values so the Tagging menu is just about how theyre being displayed to you through the viewer. If you set RGB to .5 and cycle through the tags it will adjust the display values but the working values don’t change. My guess then is that you had values either over one or below zero and applying an input transform from aces to sLog brought those values back into a range where they would play nicely with your source image.

[Unclextacy]

Thanks for that, I figured it was a illegal colour thing and did initially try clamping but none of that made any difference at all. I don’t really know enough about colour but at least I know enough to get by now, thanks again!

[Ryland]

As a wise woman once told me, “Colorspace never takes a day off.”

[johnt]

A little gotcha with the gradient node in linear space (not sure if you are doing it in linear or rec) high luma levels print through into the gradient if attached to the clip.