Animation Question

Quick question.
My goal is to get the wings behind the girl, as if they were coming out of her back.
Is there a way to cut out her shoulders and put the wings behind her?
Can I do this in FCPX or do I need to get a different application to do these types of edits?(Are these types of edits even possible?)
discussions.apple.com/message/24806141#24806141
This is the link to the photo

discussions.apple.com/message/24806141#24806141

You'll need a plugin that can make a mask shape out of her shoulder/torso and be able to track any subtle movements (or if there's a camera move). Something like SliceX would work. Duplicate the shot, mask out her body, and place it as a layer on top. The wings would be on a layer below that, and finally the original shot would be on the bottom layer.

But honestly, the thing that will make this most look like the wings are in the scene would be the lighting and modeling of the wings. Currently, they don't look very convincing, but of course doing it better would require more effects expertise/expense. Also, the compositing would be better done in a program more specialized for that, like Motion, After Effects, Flame, etc. It just depends on what you deem to be "acceptable."

Would Motion 5 Work to do the masking?

Several things.

If your talent and camera does very little movement...then you can mask the talent and get a pretty good track from the tracker in motion.

To make your wings look better, you have to bring the look of your camera into your wings. so, for instance your camera has a lot of grain to it. So, add some grain to the wings. Also, the camera doesn't have the best focus, so maybe blur your wings a bit. There is also too much color in the wings compared to the footage, so if your can maybe desaturate the colors a bit or some other way to lose some of the colors. Also adding some lights to your wings in a 3d group, and put some objects in the lights way that would resemble the trees, that way maybe you can get more realistic light on the wings.

If you can rebuild the wings in a 3d program, then the bones of the wings could use a better looking texture applied to them.

The wings fitting in is not the problem, as I have a pretty good idea how to make them fit in.
My problem is that I don't know how to mask the shoulder. It sounds like Slice X and/or motion is my best bet?

SliceX is one way. Manually keyframing a mask in Motion is another. I would try this, if I had the clip to work with myself, as an experiment.

Make a copy of the clip above itself.
Must the bottom copy temporarily.
Garbage matte out everything except the shoulders, head, chest area of the girl.
Apply an HSL keying mask to the top image, masking out the color of the clothing on her shoulders.
Invert that mask.
Add wings between the two original clip copies.
Turn the bottom one back on.

Just a thought. Will depend on how well you can key out the color of the clothing covering her shoulders, arms, chest, etc.