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To use an Alpha Channel in an overlay:
1. Background clip
2. Alpha channel
3. Overlay clip
4. Result
Using Gamma correction
Gamma refers to the gray values of a color which contribute to the levels of
highlight and shading that appear in an image. The Gamma graph is a visual guide
which allows you to change these values and thus affect changes in the highlights
and shadows, as well as change the midrange or midtone values. If you move the
gamma value higher up the graph, you darken the clip whereas moving it lower
lightens it. You can move the thumbtacks that appear along both the X and Y axis
to give you better control over which highlights and shadows are affected. The Y
axis thumbtacks represent the possible changes you can make to the grays of the
original clip. The X axis thumbtacks work similarly except they restrict you to
changing only the midtone grays of the original clip, leaving the areas with strong
highlights and shadows untouched.
CHAPTER 4: ADDING EFFECTS AND TITLES 113
1. Place a video clip into the Video1 track.
2. Place a video clip which was created with an
alpha Channel (for example, a CG Infinity file)
into the Video2 track.
3. Right-click on the clip in Video2 and select
Overlay Options to open up the Overlay
Options dialog box.
4. In the Type drop-down box, select Alpha
Channel.
At this point, the areas specified in the channel are
immediately keyed out. If the preview image does
not change, then the overlay clip does not contain
an Alpha Channel. Click OK.
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