Deploying an alpha channel as a layer mask

- [Narrator] In this movie,…I'll show you how to deploy an alpha channel as a layer mask…and I use the word deploy because…until you convert the alpha channel into a layer mask…it's not an active member of the composition,…it's just more or less sitting here.…Now, I want you to notice that you can…switch between the various channels using keyboard shortcuts…and these are shortcuts that Adobe includes by default…and so, if you press control two, or command two on a Mac,…you'll switch back to the full color composite image…at which point you may notice…that the red, green, and blue channels are all selected…because they are active ingredients in the full color image.…

If I press control three, or command three on a Mac,…I switch to the red channel and so forth.…Now it's not essential that you memorize these shortcuts…because, after all,…you can see them here inside the channels panel…but they do work when the channels panel is hidden as well.…So for example, pressing control four,…or command four on a Mac,…switches to the green channel.…