Alpha channel is a channel in a still image that defines a certain quality about an image. In an RGB image, for example, there's a Red channel, a Green channel, and a Blue channel. Then, you can add an additional channel called an alpha channel.
You can tell Premiere to use the alpha channel of a still image to determine what parts are transparent and what parts aren't.
Alpha channels are only on stills -- not video.
For example, you want a spaceship flying by the moon. You make a still image of the moon and save it as a bitmap or a pct or whatever. Bring that into Premiere and place it on Video 1. Stretch the duration for, oh, 30 seconds.
Then, in Photoshop, you make a picture of a spaceship, but you build an alpha channel around it. Save it in a file format
that supports alpha channels and then import it into Premiere, placing it on Video 2, above your moon. Tell Premiere to define transparency on that image by using the alpha channel (Video >> Transparency >> Alpha Channel). Now, you can use Image Pan or Video >> Motion to move the spaceship and wherever your alpha channel was cut, you'll see the moon behind.
Spacey!
Cheers,
![[monkey] [monkey] [monkey]](/data/assets/smilies/monkey.gif)
Edward
"Cut a hole in the door. Hang a flap. Criminy, why didn't I think of this earlier?!" -- inventor of the cat door