Hi ! Is it possible to extract the alpha channel/ depth channel of a film sequence when using a 3d camera rig for recording ?

Do you mean green screen keying or alpha channel on a pre-matted sequence? Can you explain the application?

If you are handling the left and right as two separate sequences then there shouldn't be any additional issues... just twice as much work.

Yes its possible, you need software to compute depth from stereo images. Ive searched furiously and found only the SVS software from Videre design.

http://www.videredesign.com/vision/svs.htm

They want $600 and the examples look decent, Im just itching to buy it once I get $600 lying around. If you got plenty cash then use The Foundrys Furnace plugin called zdepth $4400.

If anyone knows other alternatives please let us know.