Final Cut Pro: Using Video and Graphics Clips with Alpha Channels

In Final Cut Pro, alpha channels define areas of transparency in a video clip or still image. Regular clips only have three information channels. Those channels are red, green and blue. An alpha channel is an additional channel. The level of transparency that is applied to your video clip or still image is determined by the levels of black and white that are on the grayscale that an alpha channel uses.

Working with Alpha Channels

When working with alpha channels in Final Cut Pro, any clip that has an alpha channel in it must be on a higher numbered video track than the other tracks in your project. Clips that have alpha channels in them can be edited just like you would edit any other clip in the sequence. Whenever you import a still image into Final Cut Pro, the program will automatically set the Alpha properties for that clip.

Types of Alpha Channels

There are three different types of alpha channels. The straight alpha channel only contains pixels that were rendered for an image with no background. With the straight alpha channel, the background in your video clip or still image will appear black. If you are compositing and layering your project, straight alpha channels will work well for you because projects that contain straight alpha channels are easier to composite.

The black alpha channel is also often referred to as the premultiplied with black alpha channel. If you are familiar with drawing channels in Adobe Photoshop, you should be familiar with the black alpha channel, as most channels drawn in Photoshop are premultiplied. With the black alpha channel, your entire video clip or still image will be precomposited against black.

The white alpha channel is very similar to the black alpha channel. The only difference is that instead of your video clip or still image being precomposited against black, your video clip or still image will be precomposited against against white. The white alpha channel is often referred to as the premultiplied with white alpha channel.

Using the Item Properties Window

By using the Item Properties window, you are able to change the alpha channel that was assigned to your clip by Final Cut Pro. To bring the Item Properties window up, you must open the Browser and select the clip. With the clip selected, go to Edit then Item Properties then Format. You can also bring the Item Properties window up by pressing Command and 9. With the Item Properties window open, Control-click on the Alpha row, which is located in the Clip column. From there, you will be able to use the shortcut menu to select the alpha channel that you wish to use. If you would like to remove an alpha channel from your clip, select the None/Ignore option.

Using the Browser

You can also use the Browser to change the alpha channel that was assigned to your clip by Final Cut Pro. To do this, all you have to do is Control-click on the Alpha column. The shortcut menu that appears will allow you to choose one of the above alpha channels.

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