After Effects: Background Replacement

[fitch.j]

I'm aware this isn't the type of thing a lot of people on these boards deal with but i thought it's worth a shot to see if anyone could offer some suggestions.

I have some footage that i'm working on, and as part of the comp i need to do a background + sky replacement. I have the sky and background image that i am using, i've blended it into the comp and tracked it correctly so that it looks seamless when overlayed over the sky of the original.

I have some people in the shot who i need to show through onto this. The original though was to Roto each person for each frame and create a mask on the sky layer and have it subtract, therefore allowing them to show through, however with 2 people in shot, and for quite some frames, that is a whole lot of roto to do. I was wondering if because the background is still, i could have after effects recognise the background, and key it out leaving a layer with just the people.

I have attached some screenshots to make it easier for you to see what i am attempting to do. One of the original, One of the BG overlayed, and one of one person (badly) roto'd through.

Any help would be MUCH appreciated.

Thanks,

Jon

[guns1inger]

If you have not done the videocopilot thing, you should. If you use after effects for more than a simple line of text then there is something there you will use. The site is hosted by Andrew Kramer, who did title design for Fringe and the recent Star Trek movie, amongst other things.

The two specific tutorials you want are the very first tutorial Andrew put up on the site ; http://www.videocopilot.net/tutorials/basic_sky_replacement/ and then the advanced version, which extends these techniques ; http://www.videocopilot.net/tutorials/advanced_sky_replacement/

I doubt you will be able to avoid rotoscoping, but check a few of the other tutorials and you will be surprised at how loose some of the roto'ing can be and still work.

Lots of goodies, including free plugins and presets. Bookmark it now.

[fitch.j]

Yup VC is great, i've been using their products for almost a year now, I've also posted the same question on the forums over there so seeing what responses i get there as well. I'll rewatch the advanced sky replacement tut again but as far as i can remember there was nothing about keying in there from a still BG to extract the movement.