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[Question] How to seperate moving foreground from static bg

https://forum.blackmagicdesign.com/viewtopic.php?f=22&t=72135

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[Question] How to seperate moving foreground from static bg

PostPosted: Wed Apr 11, 2018 2:57 pm
by JoeSchroecker
Hello,

I had Fusion on my radar since forever, but never really made the step to actually use it, so I want to change that on a small project I'm currently working on. But I can't find any tutorials do point me in the right direction. Maybe I'm not using the right terms or it is so basic todo that nobody thinks of explaining it:

Situation: I have a moving foreground (eg. running person short hair) in front of a fairly static background (e.g. wall). now I want to set a Text between foreground and background. I also have a empty plate shot of the background.

how can I seperate them without rotoscoping? in AE there is a tool "roto assist" which can be a big help. How would i do something similar with Fusion? Or at least whats the terminology to search for?

Thanks a lot!

Re: [Question] How to seperate moving foreground from static

PostPosted: Wed Apr 11, 2018 3:13 pm
by michael vorberg
The best result will be to rotoscope the person, maybe tracking and the roto assist feature in the polyline/bezier mask can help.

But for a fast start you could try to use a difference key, if you have the same background with the same camera movement


Rotoscope will should give you a better mask, if done right. There is a reason why a whole roto department exists in major vfx studios

Re: [Question] How to seperate moving foreground from static

PostPosted: Thu Apr 12, 2018 8:57 am
by JoeSchroecker
Ah ok, I would have bet that there is a smarter way by now with sophisticated software, but it seems not.

I will try the difference way, then I hate to waste hours on rotoscoping

Re: [Question] How to seperate moving foreground from static

PostPosted: Thu Apr 12, 2018 9:06 am
by alan bovine
JoeSchroecker wrote:Ah ok, I would have bet that there is a smarter way by now with sophisticated software, but it seems not.

I will try the difference way, then I hate to waste hours on rotoscoping


If you can find a better way you'll be rich. Sadly none of the auto tools are as accurate and stable as good'ol roto.

Re: [Question] How to seperate moving foreground from static

PostPosted: Thu Apr 12, 2018 9:09 am
by Sander de Regt
JoeSchroecker wrote:Ah ok, I would have bet that there is a smarter way by now with sophisticated software, but it seems not.

I will try the difference way, then I hate to waste hours on rotoscoping

How much of the frame will the Text fill? If it's just a title and it's actually running, then this shouldn't take too long to roto. Certainly not hours. If it's a complete screen, then yes it will take some time.
But if you don't want to spend time on roto, spend more time on planning :-)