The alpha channel is home to the mask

Now that you know how the color bearing channels work, it's time to introduce…you to the non-color bearing channels which are known as Alpha Channels.…I explain why they're called Alpha channels in the very next movie, but for our…purposes Alpha channels contain masks.…Let's imagine a simple scenario.…You start with a standard rectangular selection where you have to convert that…selection to an Alpha Channel, everything inside the rectangle would be white…and everything outside would be black, so just as everything inside the…selection is selected and everything outside is protected, where an alpha…channel is concerned white means selected and black means protected.…

So whatever modification you apply, whether you're moving or re-coloring or…rendering something utterly unrecognizable, it will only happen to the area…represented in white, but masking is not all black and white and alpha channel…is a grayscale image.…Those grays translate to subtle transitions, soft edges, gradient fades and…