Keying and motion-tracking in After Effects

[Cracker Funk]

Two questions here. I know that I'm capable of pulling off both things, I'm just not entirely sure of the best way to do it (and I need to figure it out, cuz I'm already halfway through shooting).

I'll start with the simpler and easier of the two tasks. I want to key out not just my background, but do a reverse-key, so that I can replace my subject with a solid color, or any other video I so choose. Here's an example of what I'm talking about:

https://vimeo.com/94112398
PW: indietalk

This was a quick-and-dirty test shot. I achieved the black-on-white silhouette simply by exporting the matte view. I then tried to take this video and key out either black or white, but for some reason wasn't able to do that. At least, I wasn't able to do it using keylight. I tried a couple different plugins, and was able to achieve desired goal, but it looked crappy. I'm hoping to keep this within keylight, and I'm hoping to minimize the number of exports I have to do.

Any ideas?

Okay, now for the more complicated question -- I'm shooting actors on a green-screen, and I'm going to place them within a miniature set. And the kicker -- I'm using a crap-ton of dolly shots, and I don't have any automated computer equipment to make the full-size and miniature movements match. I'm keeping the movements slow and simple, and am relying on math and a steady hand to keep the camera movements in close proximity to each other.

I feel confident that I can keep the movement close to each other, but of course it won't be perfect. Thinking I'm gonna need motion-tracking to line up the shots. Here's my question --

Do you think I should simply line one shot on top of the other, with a few tracking points? Keep It Simple, Stupid?

Or, should I create a virtual plane and then lay both shots on top of that?

Your thoughts are much appreciated, and any links to useful tutorials would be rad. Thanks!

 

[Caidh Mor]

1) If you've already gotten a clear black and white, then just Luma matte that footage, it'll key out the white perfectly.

2) Personally I'd just lay the two layers atop one another. Just make sure that, if possible, you set your tracking markers up the same distance away as you want the background elements to be; it'll save you a ton of time.

 

[WalterB]

Indeed: Luma matte (or inversed)
You don't even need to export: then you can used the keylayer as Alpha matte (but if the project is big it can slow things down compared to an exported and imported black and white video).

Otherwise use extract: it's a luminance key effect.

 

[jax_rox]

1) as has been said, luma matte/key. I'm sure there's a simpler way to do it all in one in key light, but it's probably been 2 years since I've opened up AE for anything other than the occasional warp stabilization so I'm not really sure where to point you.

2) I think I'm assuming correctly if I assume that you'll be doing two dolly moves and trying to match them up later?
What will you be shooting on? Any chance you could go with something with a bit higher resolution (GH4k?)?. If you shoot in higher resolution, framing to take into account some post re-framing, you could potentially shoot still frames, and do the entire dolly move in post. Otherwise, you could still do the dolly move, but the extra res would allow you a bit of wiggle to match them up better.

 

[Cracker Funk]

Cool, luma matte it is. I haven't done it yet, but since three of you are telling me the same thing, it sounds like that's clearly the way to go. Thanks!

Jax, you assume correctly. There's a full-size dolly move, and a miniature dolly move, and I need to match them up. I can't do a fake-dolly in post because for these particular shots, it's essential that images in our peripheral move in a true 3d environment (plus, I'm almost done shooting the full-size shots).

Though I can't shoot at a higher res that you suggest, I'm actually already kinda on the same page as you, just in the opposite direction. I decided, beforehand, that the final video would be 720p. I'm shooting at 1080p, giving myself plenty of wiggle-room for cropping (and motion-tracking).

As for motion-tracking, I'm planning on following the good-ol' video copilot. Any alternative suggestions?