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Adding luma information from key layer back to composited video

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Scott Rosen
Adding luma information from key layer back to composited video
on Feb 23, 2015 at 5:54:28 pm

Hi all,

Not sure if this is a stupid question or not -- I'm guessing there's an obvious way to do this of which I'm not aware. I'm using AE CS6.

I have a green patch (green gaffer's tape - about 6" x 4") on an actor's black shirt, in a medium shot. The effect I'm going for is to composite video onto this patch, such that the video appears to be part of the shirt.

I'm 90% of the way there -- I'm using perspective corner pin tracking to get the perspective right as the actor moves. I'm scaling up to get enough coverage of the complete patch, then keying the scene so that the composite matches the outline of the green patch. It's fairly convincing in the sense of shape and perspective.

What it's lacking is shadows (e.g. folds in the shirt). What I'd like to do is take the luma information from the green patch and use that as a mask for the composited video. The goal being to reproduce the highlights/shadows of the green patch onto the final composite.

So I have two questions: Am I going about this the right way in the first place? And how can I overlay the shadows from the green keyed area onto the composite?

Thanks in advance!

Scott


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Walter Soyka
Re: Adding luma information from key layer back to composited video
on Feb 24, 2015 at 3:59:00 pm

You could use Shift Channels, taking Red, Green and Blue from the Green channel to get the luminance in the patch. Use a Levels or Curves effect to tweak the values as you like. Use a multiply blend mode to lay the shadows back on.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Scott Rosen
Re: Adding luma information from key layer back to composited video
on Feb 25, 2015 at 5:10:36 am

Thanks Walter, worked better than my solution.

After I posted my question, I ended up getting to a very similar solution, but I used the B&W effect instead of shift channels.

I added another layer of the original source material (with the green patch) above the keyed in layer, but below the source layer. I applied a B&W effect to the intermediate layer, then did a multiply blend on that layer.

B&W resulted in a darker image though.


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Matthew Wood
Re: Adding luma information from key layer back to composited video
on Mar 2, 2015 at 9:58:05 am
Last Edited By Matthew Wood on Mar 2, 2015 at 9:58:40 am

You could reverse key a layer, leaving only the green patch, and use that as a matte.

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