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Lesson 2. About Digital Video Editing > Understanding transparency and superimp...

Understanding transparency and superimposing

Transparency allows a clip (or any portion of a clip) to reveal a second, underlying clip, so that you can create composites, transitions, or other effects. A variety of transparency types are available in Premiere. The transparency types are described in this section.

Matte or mask

An image that specifies transparent or semitransparent areas for another image. For example, if you want to superimpose an object in one clip over the background of another clip, you can use a mask to remove the background of the first clip. You can use other still-image or motion graphics software (such as Adobe Photoshop or Adobe After Effects®) to create a still-image or moving (traveling) matte and apply it to a clip in your Premiere project. A mask works like a film negative; black areas are transparent, white areas are opaque, and gray areas are semitransparent—darker areas are more transparent than lighter areas. You can use shades of gray to create feathered (soft-edged) or graduated masks.

Alpha channel

Color in an RGB video image is stored in three color channels—one red, one green, and one blue. An image can also contain a mask in a fourth channel called the alpha channel. By keeping an image together with its mask, you don't have to manage two separate files. (Sometimes, however, saving a mask as a separate file can be useful; such as when creating a track matte effect, because the mask must be placed in a separate track in Premiere's Timeline.

A 32-bit frame has four 8-bit channels: red, green, blue, and an alpha channel mask.

Programs such as Adobe Photoshop and Adobe After Effects let you paint or draw a mask and use the alpha channel to keep the mask with the image or movie. Premiere uses the alpha channel for compositing.

Photoshop image (left) contains an alpha channel mask (center) which Premiere uses to composite the subject against another background (right).


Finds pixels in an image that match a specified color or brightness and makes those pixels transparent or semitransparent. For example, if you have a clip of a weatherman standing in front of a blue-screen background, you can key out the blue and replace it with a weather map.


Allows you to control the degree of overall transparency for a clip. You can use opacity to fade a clip in or out.

With Premiere, you can combine the transparency options described here. For example, you can use a matte to remove the background from one clip and superimpose it over a second clip, and then use opacity to fade-in the first clip's visible area.

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