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Keylight--'final result' vs manually applying the matte

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Eric Mercado
Keylight--'final result' vs manually applying the matte
on Jan 25, 2018 at 9:10:20 pm

Hey,

So does anybody know a little bit about how the 'Final Result' setting of the Keylight effect works? From what I understand, the basics are that it will send an output that consists of the RGBs premultiplied by the alpha channel (unless of course you check the 'unpremultiply checkbox'). This is great.

Knowing this, I would think that I could instead set the output to 'Combined Matte,' which will send the alpha into each of the RGB channels, and then I could manually grab one of these channels using the "set matte" effect and apply it to the RGBs of the source video and get the same result. However I do not get the same results.

The Keylight "final result" mode gives me a much cleaner result than if I were to use my own "set matte" effect. Does anybody happen to know what that is?

Thank you in advance for any help!


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Dave LaRonde
Re: Keylight--'final result' vs manually applying the matte
on Jan 25, 2018 at 11:33:14 pm
Last Edited By Dave LaRonde on Jan 26, 2018 at 12:31:30 am

I don't think it's much of an advantage to do any of that. The final determining factor for whether or not the alpha-channeled file will be straight or premultipled lies in the AE Output module. The Unmultiply Result just affects the look within Keylight.

I don't see any advantage in jumping through all the hoops of using Set Matte or Channel Combiner, either. Keylight does have pretty darned aggressive spill suppression in Final Result which can create noise in the keyed image, especially in poor lighting conditions. If that's the case, you can still pull a good key -- noise and all -- using the Status view as your guide. Once you have it, it's a snap to use the keyed layer as an Alpha Matte for the same unkeyed clip, then apply spill suppression to the unkeyed clip. Lots easier!

Keylight ain't bad for what it does. If you have to go through all the rigamarole you describe, you probably have poorly-lit footage, highly-compressed footage or both.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Eric Mercado
Re: Keylight--'final result' vs manually applying the matte
on Jan 29, 2018 at 6:21:33 pm

Hey thanks for the reply Dave!

You are correct, the footage that I have is poorly lit with a pretty uneven background that I was trying to deal with (there's a pretty noticeable spotlight on the greenscreen behind the talent).

I come from a Nuke background so I my instinct was to treat the RGBs and Alpha channels separately and then recombine them after all color correction/de-spilling/etc. Something that can be a bit confusing when dealing with After Effect's layers rather than nodes haha. I'm still working on adjusting my workflow within After Effects.

Thank you for your help and suggestions!


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