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Difference mask or differential mask - keying against a static, locked shot

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Adam Sherds
Difference mask or differential mask - keying against a static, locked shot
on Apr 6, 2018 at 3:53:26 am

Hi, Everyone.

I'm trying to do what some call a "difference mask" or "differential mask" in Final Cut Pro or Motion.

I have a locked shot, an empty plate frame with no movement, and footage where an object moves. I'd like to create a mask that tracks the moving object.

If this isn't doable in Final Cut Pro, maybe it's doable in Motion? Either is fine, though easier if it can be done natively in FCP. Fallback is Premiere, so if that's the only way and someone here happens to know of a discussion on it....

Ultimate goals:
1) place one moving object into a slightly different version of the same footage
2) color correct just the moving objects in other shots without rotoscoping.

Can someone please either suggest a workflow or plugin (preferably free or lower cost), else point me to an existing discussion on how to do this? Or suggest other search terms so I can find this? Guessing this is answered somewhere, but so far has been hard to find.

To illustrate the goal, I've included two pics below.
— The first is the empty plate (i.e. background) on which I'd like to use a keyer that automatically sets this as baseline.
— The second shows an item moving. I'd like to auto-create a tracked mask that follows that moving object (without manually rotoscoping and moving 40+ mask points).

I think the Kinect or similar game systems have games like this, where everyone leaves the room, it gets a baseline before picture, and then it can key everyone into a different background location.

If you know how to do this or of a good discussion on it somewhere, I'd appreciate it!

Thank you.





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Jeremy Garchow
Re: Difference mask or differential mask - keying against a static, locked shot
on Apr 6, 2018 at 8:57:02 pm

Are you saying you want to move the mixer around?

I’m a bit unsure of what you are trying to do. From what I can gather, you want to separate the mixer from the background which is the desk, box, and wall?

A difference mask may help, but it won’t be all you will need.


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Adam Sherds
Re: Difference mask or differential mask - keying against a static, locked shot
on Apr 6, 2018 at 11:14:08 pm

Hi, Jeremy.

Yes, would like a mask that stays tracked on any moving objects or any objects not in the empty plate shot.

Goals include...
  • color correction on just one item or items not in empty shot
  • adding/removing items
  • taking the moving item from one clip to another (e.g. a take with slightly different bkground lighting to match takes)

Thanks.


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Adam Sherds
Re: Difference mask or differential mask - keying against a static, locked shot
on Apr 13, 2018 at 11:15:55 pm

Jeremy and others.... So does anyone know how one can do a difference mask please?


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Jeremy Garchow
Re: Difference mask or differential mask - keying against a static, locked shot
on Apr 14, 2018 at 12:43:59 am

MochaPro is fantastic for tracking/roto

Mocha technology is present in an FCPX plugin called Track X (and Slice X).

Mocha combined with after effects or another composting application will offer the most flexibility, but it’s a fairly steep learning curve.


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Simon Ubsdell
Re: Difference mask or differential mask - keying against a static, locked shot
on Apr 14, 2018 at 9:24:17 pm

It's a pain to do this in FCP X but very easy in Motion.

Here's a sample project to show how it's done.

12352_differencematte.zip

Essentially all you need to do is layer the two versions of your shot and set the blend mode of the upper layer to Difference. Use the Channel Mixer on the group to create a luminance only version. Then use a Threshold filter (or a simple Levels) to adjust the resulting "matte".

All you then need to do it apply the matte to the element that you want to cut out by creating an Image Mask for that layer and then adding the group with the difference matte to the Image Mask source well and setting the Source Channel to Luminance.

Simon Ubsdell
tokyo productions
hawaiki


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