How do I remove everything except for one color?

[Vaishnav5CFC]

I have a scene from which I'd like to remove everything in the background (the hologram part) and leave the foreground (the black silhouette part) so I have a transparent background. How can I do this? Any help would be appreciated!

[Ann Bens]

Rotoscoping in Ae would be the best option, but you could try the mask from opacity.

[Richard M Knight · Accepted solution]

You could try a luma key but you would end up with the rail as well.

[Vaishnav5CFC]

I actually needed the rail as well. Luma Key worked perfectly, thanks a lot!