Yeah that’s exactly what i do but i don’t seem to get the BG coming through. Could it be a despill issue?
As long as you are using master key with only the green being targeted it should be ok.
Worst case would be building it manually
I built it manually and had more success with adjusting the the 2d histogram but the results were far from the plate.
I have an example that I think has a similar issue to the one you are experiencing @Ben :
This is a screen grab of my subtract node from my IBK setup. LHS is my clean plate with my matte multiplied. Middle is my original plate and the RHS is my green subtraction.
Can you see the strange dark blue edge?
See what it does to my comp:
Copy, what about adding a cc after the comp and grading back a bit of a soft matte of where the key would be
Can you take a look at the red channel of your green screen plate?
Does that highlight the same problem area?
I dont think i have the same issue but sometimes the car window has a similar line but is red as opposed to blue
An IBK seems to pull the key alright but the green subtraction creates that horrible negative black edge.
If I were you I would take the alpha output but try a totally different green suppression. IBK is making a real mess of that edge. If you are using MK you will need to reduce the luma a significant amount to match the background plate.
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Yeah i cant put my finger on what is causing the issue. Did you denoise the plate first?
Could it be how the plates has been handled in DI? Maybe the raw would yield better results?
Have you tried putting a clamp on your matte?
Yeah. It’s not that. It is caused by the green subtract. That part seems to cause negative values. Even if the matte is clamped.
Not negative values (edit- not negative in the alpha. IBK green subtract did cause those black negative values). Not ACES. Just a very tricky green screen key.
The background is so dark it is almost black and you will struggle comping black into any green screen.
I would be prepared to rebuild the hair and soft edges. Anything that has a soft fall off into the green screen will give you a bright edge when comp’d over the dark background.
Try grading down the plate but I think that you will end up rebuilding.
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Initial thought was you’re using the result output on the ibk with it set to comp/premutiplied and have adjusted the red and blue sliders on the ibk too far. Using only the matte output and a seperate branch with whatever despill you want shouldn’t give you any funky edges
@Ben if you can share a small snippet I can look at it Saturday morning.
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Sorry Randy I’ve only just seen this message. Mich appreciated
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What version of Flame are you running?
Still on 2019 
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And what colorspacr are these exrs?
They should be ACES AP0. Thanks for taking a look, the sequemces has been the pain of my life over the last few days haha