… for Apple Motion
Tip #433: Why Display Alpha Channels
The alpha channel displays the transparency in a clip.
One of the options in the top right corner of the Motion Viewer is the ability to display the alpha channel of the current project. (You’ll find it in the menu under the color square.) But, why would you need this?
The alpha channel, like the red, blue and green channels, displays the amount of transparency associated with each pixel. For instance, in this screen shot, does the gradient in the top, color, image fade to black or transparent? It’s impossible to tell.
However, when you look at the bottom image, which displays transparency, it is easy to see that the image fades from solid black (transparent) to solid white (opaque). (Shades of gray represent differing amounts of translucency.)
Remember, the alpha channel doesn’t show color, it shows transparency.