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Extract person in front of projector using blending mode?
Hi there!
I have a simple setup: Filming a guy talking and his powerpoint presentation. Lighting is very unfavorable in such a setup and the choice of aperture is tricky because either the presenter is too dark or the screen is too bright. So I decided to set the aperture for the presenter and will replace the overexposed presentation in post.
Now the issue is, the presenter walked a few times in front of the screen and when I put the powerpoint in a layer above the video, he will then disappear behind. Which doesn’t look good.
So I could just mask him out and put that on the top layer. But this would take me forever.
The camera is on a tripod and doesn’t move. I have footage of the background without presenter. Is there a way to extract the presenter from the background? I thought about blending modes for example.
The result should be a transparent video with only the presenter.
In short: I want take away all content that is the same as the background layer.
Thanks for your help!
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5 Replies
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Try the effect called “Difference Matte”. You can freeze frame the clean background on another layer and use that to extract the person.
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If there’s major contrast between the subject and the screen, a luma matte might also be possible. Can you post a screen grab so we can see what you’re working with?
In practice, I find Difference Mattes to be unreliable in almost all situations, because as soon as the camera shakes a little, you’re hosed–every single pixel will be slightly different than the source frame.
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Hi!
Yea i think that’s the effect I am after! But I tried to apply it but I don’t get the result needed.
So I have two layers. Bottom layer: The original video where I freeze frame a clean image without the presenter, leaving just the plain background.
The top layer with the difference matte effect. I choose the bottom layer as masking layer. But thats doesn’t show me anything useful.
What am I doing wrong?
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You may need to precompose the freeze-framed layer using “move all attributes”. Then turn off the precomp.
Duplicate your presenter footage. The bottom copy is your background. Top copy is the extracted presenter. The difference matte goes on the top copy. Choose the precomposed freeze-frame in the “Difference Layer” dropdown.
You powerpoint can now go between the presenter layers.
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Precomposing did the trick!
Thanks for all your help! This is exactly what I was looking for!
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