Difference Matte Help

I’m working on a video for a friend. I’m trying to take out the background by doing a “difference matte” effect, but there is no green screen. I know it is possible to do this with nodes but have no idea how to. Could someone post a tutorial or link to one please?

Very difficult to do unless the scene is shot properly. Sounds like the “fix it in post” dilemma.

But here might be some useful intel:
http://www.digitalvideofuel.com/transwogreen.htm
http://forums.creativecow.net/thread/2/923637

As I understand it difference mattes rarely work because the margin of error is so ridiculously small. Video compression or film grain can be enough to torpedo a difference matte.
http://forums.macrumors.com/showthread.php?t=223415

Oooh: http://help.adobe.com/en_US/AfterEffects/9.0/WS3878526689cb91655866c1103a9d3c597-7b4ba.html

I think you’ve confused color difference matte with difference matte. Regular difference mattes are rarely useful except for garbage matting (paraphrased from our bible.)

Have you considered rotoscoping, mind numbing and painful I know.

http://www.gregnotzelman.com/pages_vfx/pages_prj_vfx/blend_roto_nw.html

How good is you’re video source, the compression, interlaced and speed of movement in and out of the frame, that will have an effect on the quality and effectiveness of the difference matte I’d guess.

see 8th video tut in the album http://www.vimeo.com/album/16278

You might also consider Claxa for rotoscoping. You simply outline the object in one frame and the software modifies it for each frame and creates the matte.

http://www.patchmaker.net/Claxa/

I’ve had pretty good luck with that.

Another option if you want to continue to try the difference matte route is the CineGobsKeyer.

http://www.cinegobs.com/

It allows you to add several mattes together and is pretty easy to use.

Both are freeware, but are Windows only, I’m afraid.