This is more of an advanced chroma-keying (or “Green Screen/Blue Screen”) project, as is done almost entirely in After Effects CS4, but doesn’t require any external or third-party plug-ins. Only Keylight, which ships with the software. There are several tutorials out there that show you how to get a simple Green Screen background keyed-out but what if your actor is “sandwiched” between two planes, like peeking around a corner? That’s where you will need to shoot it with both green and blue screen planes.
I chose this Santa footage for this project, because it utilizes both Green Screen (for the background) and Blue Screen (for the foreground) all in one shot. This complex keying shot uses two passes with the Keylight chroma-keyer in After Effects CS4 to accomplish the “sandwich” of Santa between the two screens.
I first needed to line-up the green screen footage layer with the background layers used in this composite, so I set a guide on the edge of the door and moved/rotated the green screen footage to line up the edge of the blue panel with the guide. I then create a large feathered mask around the live action portion of the screen footage as a “garbage matte”.
I then use the Keylight keyer filter on the green background and fine-tune the settings to get the best possible key of the Santa character. (Oooh… he looks a little pissed here, doesn’t he?) 
Next I use the Keylight filter on the blue foreground panel and adjust to accommodate for the shadows from his hands, so the door shows through.
Lastly, I use the Levels filter to adjust the color of the keyed character to attain the best color and lighting for the composited scene.
You can see the before/after video of this process in the movie link below:
NOTE: YouTube screws up the first few seconds by over-compressing the video, but it clears up – just let it keep running!
To see this tutorial in step-by-step detail, you can get my new training DVD here: “Learning After Effects CS4″ from PhotoshopCAFE.com
In future articles, I will cover tips on shooting a good Green Screen on a budget (who doesn’t need THAT?!!)
Also – you can check out my Blog for more Photoshop and After Effects tips & tricks here: http://AfterEffectsandPhotoshop.com
Cheers!
Jeff
