Adobe PREMIERE PRO 2, Руководство пользователя, Страница: 362 / 448

ADOBE PREMIERE PRO 2.0
User Guide
356
alpha channel in the Program Monitor, white areas indicate opacity, black indicates transparency, and gray indicates
partial transparency. Because an alpha channel uses shades of gray to store transparency information, some effects
can apply a grayscale image (or the luminosity values of a color image) to an alpha channel.
Mask
Describes the process of modifying an alpha channel; sometimes used as another word for alpha channel .
Matte
Defines or modifies the transparent areas of its clip or another clip. A matte can be a file or channel. You might
use a matte when you have a channel or clip that defines the desired area of transparency better than the alpha
channel, or when a clip doesn’t include an alpha channel.
Keying
Defines transparency by a particular color (chroma key) or brightness value (luminance key) in an image.
Pixels matching the key color become transparent. Use keying to remove a background of a uniform color, such as a
blue or green screen.
Separated color channels (left), the alpha channel (center), and all color channels viewed together (right)
See also
“About transparency” on page 354
“About alpha channels and mattes” on page 354
“To choose a display mode” on page 101
Compositing clips
Each video track in the Timeline panel contains an alpha channel that stores transparency information. All video
track frames are completely transparent except where you’ve added opaque content such as video, still images, or
titles. You can make areas of opaque content partially or completely transparent by adjusting a clip’s alpha channel
or applying a matte or key to a clip. Clips on upper tracks cover clips on lower tracks except where alpha channels
indicate transparency. Adobe Premiere Pro composites clips from the lowest track up, and the final video frame is a
composite of clips on all visible tracks. Areas where all tracks are empty or transparent appear black. If necessary, you
can use the File > Interpret Footage command to change how Adobe Premiere Pro interprets a clip’s alpha channel
throughout a project.
Keep the following guidelines in mind when compositing clips and tracks:
•
If you want to apply the same amount of transparency to an entire clip, simply adjust the clip’s opacity in the Effect
Controls panel.
•
It’s often most efficient to import a source file already containing an alpha channel defining the areas that you want
to be transparent. Because the transparency information is stored with the file, Adobe Premiere Pro preserves and
displays the clip with its transparency in all sequences where you use the file as a clip.
•
If a clip’s source file doesn’t contain an alpha channel, you must manually apply transparency to individual clip
instances where you want transparency. You can apply transparency to a video clip in a sequence by adjusting clip
opacity or by applying effects.