Question about Video backgrounds?

Most editing tools allow for basic keying. There is even the free cinegobs keyer, which is quite good.

However these all depend on you having planned for this ahead of time, and having shot the video of you in front of a green or blue screen , with proper lighting etc.

While you can sometimes extract something after the fact using rotoscoping or difference keying, it is generally a lot harder to do, takes a lot more effort, and produces lower quality results.

I think lowell meant that "difference" means chromakeying...You'll never be the only difference without a greenscreen. This is why greenscreens are so popular and heavily used. You can be in Egypt in one shot and Hoboken the next. You can be on a large virtual set. But the short answer to your question is, unfortunatley, no. You'll need to shoot in greenscreen first...then switch the backgrounds in post. The only alternative I can think of is cutting yourself out frame by frame...(unfortunately, all frames would turn out slightly different)...and then switch backgrounds to whatever. But at 30 frames per second, this obviously would be a huge time-consuming task for even a few seconds.

Or you can rotoscope (i.e. draw mattes for every frame).
http://www.voidix.com/Rotoscope.html

Originally Posted by lowellriggsiam

zoobie, there is a function in Sony Vegas called "difference" that makes comparisons from one picture to another without chromakeying, simply eliminating everything but the differences bewteen the images. So if I took a picture from in front of my house and another with me in front of it "difference" would remove eveything but me as I were the the only thing different.

It is rare that difference gets a clean separation but it certainly helps with manual matte creation. Even a small lighting difference (e.g. a cloud filtering the sun) will ruin a difference matte. Green screen chromakey is much more reliable.

I took a peek at difference masking. The methodology makes brain surgery look easy. The tutorial also tells how to fix bad spots where the separation doesn't quite work. Too bad it can't be simplified...I may be tempted to mess with it.
http://www.sundancemediagroup.com/articles/dayvids/difference_masking_in_sony_vegas.htm
I'm going into a video studio with talent this winter to goof with their green screen. The only thing I don't like is that it usually cuts off their legs because they don't want anyone walking on it.

At this point, I'm just looking for a studio big enough for the talent to run around in...which is the fun part.
Seems you need a bunch of room for the camera to be backed away from the green screen for those crazy wide-angle shots

PS - You know, I just read the OP's post again. If your "plane white wall" is pretty much evenly lit, you could just key that out with software.

PSS - I see where Tubetape.com has become an advertiser here at VH...They've got some good stuff...like that green screen costume with hood...with better prices than most