So I'm working on a clip (shot with a GL2) where I make a car explode in post (who hasn't done that, right?), but I'm having problems with something. It's really all one shot (no green screen involved), and then I duplicated the foreground and masked it, put the explosion over the background, and watched it. My problem is the guy in the foreground is moving so much and with sparatic (sp?) movements that it's hard to mask without it looking like a bad greenscreening. Any ideas of how to solve this?

I tried bringing in the mask by a few, and then feathering it out by a mere 1 or 2 (which was a drastic difference) to give it that "glow around" feel from the explosion, but it still is rough. I'm not looking for hollywood production here, but I want to be happy with it before I show it to even my friends.

im just thinkning here and had thought about this before but did you try keying with the colour picker. take out the surrounding perimeter of him this way, instead of masking.

you may need to apply the effect a few times, each with a slightly different picked colour. In theory this method could be used to isolate any element from any footage. I suppose its down to the vibrancy and contast of the differing colours(related to tolerance), quality of footage (ideally HD but anyway) and patience.

maybe worth a try?

use the inner-outer key: you've already drawn/animated the mask which is the most tedious part of that effect.

I'm not familiar with inner-outer key. Can you explain a little further?

I'm not familiar with inner-outer key. Can you explain a little further? I learned about it from a private-citizen's tutorial online about it, but the site didn't jump out of a google.

The adobe website gives us:
http://livedocs.adobe.com/en_US/AfterEffects/8.0/help.html?content=WS3878526689cb91655866c1103a9d3c597-7b47.html
(You've got to click the plus-sign next to "Use the Inner/Outer Key effect")

Basically, you trace the inside edge of your object with a bezier poly (create a mask on the footage layer to be keyed) and tell the effect to use that mask (once the mask is drawn, it's name will appear in list in the effect controls) to define the boundaries of your obejct. You can refine it by tracing a mask outside the object's edge as well. Colors that cross pixels the inner bezier are kept, colors that cross the outer bezier are discarded. Kinda like a magnetic lasso for keying.

Hey thanks! I actually went in, tightened the mask, and added a glow to the explosion which made it seem a lot better. Then with a simple addition of the wiggler and a motion blur, no one will be the wiser. :-)

cool, glad you got a good result

edit

found that tutorial, probably read about it here...

http://www.creativemac.com/2003/01_jan/tutorials/innerouterkey.htm

Oh wow, I had no idea how incredible this was! Brilliant!

do you still have to keyframe or motion analyze the footage to keep the garbage matte in place? for instance the smoke....it changes constantly as it flows so does the keyer know to keep the color range that you have previously told it? thanks.

do you still have to keyframe or motion analyze the footage to keep the garbage matte in place? for instance the smoke....it changes constantly as it flows so does the keyer know to keep the color range that you have previously told it? thanks.
Yep, that's the downside for me. You have to manually animate the mask to match your footage, so I've ended up using the various color-based keying options instead. But then I mostly get my footage against green-screens. Honestly, I'm not sure that the smoke example is the most practical-- it was shot against a solid background so it should be a fairly simple color-key requireing no mask animation-- but it is a good demonstration of how well inner-outer works on fuzzy edges.

That's what I was curious about as well. I didn't understand why they didn't just use keylight to get that background out. So this can be used if the smoke was actually outdoors and you wanted to use it later?

That's what I was curious about as well. I didn't understand why they didn't just use keylight to get that background out. So this can be used if the smoke was actually outdoors and you wanted to use it later?


I'm not sure keylight was available when those tutorials were posted. (and if you know of any good keylight tuts, I'd love to see them...) I've not tried it, but the implication is that inner-outer would be better than your other (slim) options for lifting just the smoke from a complex bg.