Adobe Premiere Pro CS6 - Manual (Page 461)

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proportion to their degree of transparency.
Some software lets you specify the background color with which the channels are premultiplied; otherwise, the background color is usually black or
white.
Straight channels retain more accurate color information than premultiplied channels. Premultiplied channels are compatible with a wider range of
programs, such as Apple QuickTime Player. Often, the choice of whether to use images with straight or premultiplied channels has been made
before you receive the assets to edit and composite. Premiere Pro and After Effects recognize both straight and premultiplied channels, but only
the first alpha channel they encounter in a file containing multiple alpha channels. Adobe Flash recognizes only premultiplied alpha channels.
About keying
Keying is defining transparency by a particular color value (with a color key or chroma key) or brightness value (with a luminance key) in an image.
When you key out a value, all pixels that have similar colors or luminance values become transparent.
Keying makes it easy to replace a background of a consistent color or brightness with another image, an especially useful technique when you
work with objects too complex to mask easily. The technique of keying out a background of a consistent color is often called bluescreening or
greenscreening, although you don’t have to use blue or green; you can use any solid color for a background.
Difference keying defines transparency with respect to a particular baseline background image. Instead of keying out a single-color screen, you
can key out an arbitrary background.
Keying in Premiere Pro is performed with keying effects. For more information, see Keying effects.
Blend clips with a Garbage Matte effect
You can use a Garbage Matte effect to blend images. For more information about using the Garbage Matte effect, see Eight-Point, Four-Point,
and Sixteen-Point Garbage Matte effects.
Blend clips with a matte using the Track Matte Key effect
You can blend clips with a matte (typically, a black and white image, or an image from the Titler.) using the Track Matte Key effect. For more
information, see the article, Track Matte Key effect.
This video shows how to create a track matte effect.
Specify clip opacity in a Timeline panel
1. Expand the view of a track, if necessary, by clicking the triangle next to the track name to expand its options.
2. If necessary, click the Show Keyframes button , or the Hide Keyframes button , and choose Show Opacity Handles from the menu. A
horizontal opacity control rubber band appears in all the clips of the track.
Note: If no keyframes exist on the track, the rubber band appears as a straight horizontal line across the entire track.
3. In a Timeline panel, do one of the following:
Select the Selection tool, and drag the opacity control rubber band up or down.
Select the Pen tool, and drag the opacity control rubber band up or down.
The opacity value and current time appear as a tool tip as you drag.
4. (Optional) To animate the Opacity effect over time, first set keyframes. Select the Pen tool. Ctrl-click (Windows) or Command-click (Mac OS)
on the opacity control rubber band with the Pen tool wherever you want to set a keyframe. Then drag each keyframe up or down to set its
value. For example, to fade a clip in, create a keyframe at the beginning of the clip and another a few seconds later. Drag the first down to
the bottom of the clip at 0 opacity. Drag the second up to 100%.
For information about adjusting opacity in the Effect Controls tab in the Source panel, see “Opacity” on the page: Fixed effects.
You can use either the Selection tool or the Pen tool to move keyframes or Opacity handles. To adjust the smoothness of the animation,
change the keyframe interpolation from linear to Bezier.
Compositing tips
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, 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.
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