To separate a subject from a background, you can either:
1. shoot in front of a greenscreen/bluescreen, then key out the background in postproduction
You can also key out a background that is much darker or brighter than your subject, but it usually takes a little more work, because often your subject will have pixels that are darker and/or lighter than the background, so there there will be holes in your subject that must be “patched” with a garbage matte. If your subject is not moving much, this is much easier than if you have to do a lot of keyframing on the matte.
*NOTE: there an excellent section on lighting a greenscreen on this DVD:
2. have a team of rotoscopers (or just you) manually “cut” the subject out of the background frame by frame
There are advanced tools that help rotoscopers, but consider how long it takes to do a decent job cutting a subject out of the background in Photoshop. Now multiply that by 30 and you have one second of footage.
So, if it takes you 5 minutes per frame, that’s 150 minutes per second of final footage. For a ten second sequence, that’s 1500 minutes, or about 25 hours of work. For a national spot, this is probably worth it!
For a minute of final footage, plan for 150 hours of work! A team of three people could get this done in a week.
If you’re using Final Cut Pro, you might need more than 8 points, sadly.