using single RGB channel as black and white mask

[donaldm49566304]

How can I remove the blue channel from a some footage to use it as a black and white mask? So easy in Photoshop but I can't figure it out or find a tutorial for it in after effects.

[Rick Gerard]

There are several ways to use the blue channel for a matte. Probably the easiest is to use Set Channels. 

Here I have turned off all of the color channels and am setting the Alpha Chanel of the layer to Blue.

You can even point to another layer.  Let us know if that does not do it for you. There are several other ways to manipulate channels in After Effects.

[donaldm49566304]

Wow, a reply from an Adobe Legend!

Thanks, that works well.