|Creating a file with alpha from a flat image file.|
A lot of times when producing a video I will ask the client for their logo and I'll get back a graphic file with the logo matted over a background color. If I want to use this graphic, it's always best if it has an alpha channel before I bring it into an editing application.
|The logo from which I will be extracting an alpha channel.|
Keep in mind that I work on a Mac, if you are using Windows, the COMMAND key on the Mac does what the CTRL key does on Windows and the OPTION key on Mac is the same as the ALT key on Windows.
|The Channels tab in Photoshop.|
Since the logo I am working with in this example is made up of 2 colors, white and orange, I will make a copy of the Red channel. The goal is to make all of the opaque parts of the image white. If necessary, use Levels… under the Image > Adjustments menu to bake sure the opaque parts are 100% white and the transparent parts are 100% black.
Use this finished channel to Load Selection (COMMAND-CLICK on the channel), select the RGB (COMMAND-2) channel and go back to the Layers tab. It's now time to create a solid layer for each color used. When you create a solid with a selection, the solid will fill that selection by way of a mask. On my example, I use white for the first color, then I duplicate that solid and place it below the original graphic and monitor only the layer that has the original graphic. This allows me to sample the orange color in my logo.
|Removing the orange spark.|
|The final logo with an alpha channel.|
You now have a clean logo with an alpha channel. When you key this over your video, there will be no halo effect around the edges.