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To use a blue screen effect in an overlay:
1. Insert the video clip that you want to be in the background into the Va or
the Vb track.
2. Insert a video clip shot with a blue screen in the background into an
overlay track, V1 for example.
3. Right-click on the overlay clip (the blue screen clip) and select Overlay
Options. The Overlay Options dialog box opens up.
4. Click on the Type list and select Blue Screen.
5. Click the Eyedropper on the blue portion of the clip in the Overlay clip
box.
6. The underlying clip will appear behind the overlay clip, in the blue screen
areas and in the Overlay preview box. (If the blue screen is not totally
replaced by the underlying clip, increase the Similarity value.)
7. Click OK and preview the clip.
Understanding Alpha Channels
One of the most powerful methods of creating transparent overlays involves
using Alpha Channels. This technical term simply means an area or areas
of an image that have been selected to be transparent in an image or video.
In many ways, an Alpha Channel is the same as a color key and could be
based on a color in a clip. Many image editing programs allow you to create
and save Alpha Channels and it is the technique employed by CG Infinity to
control transparency. TGA and TIF image files both support Alpha Channel
transparency and make excellent overlays. Because you can control the level
of transparency with 256 levels of gray, Alpha Channels are also used in
Video Paint anytime you use a matte, as well as in transition effects such
as wipes and dissolves. Most overlays in MediaStudio Pro take advantage of
Alpha Channel. Because this is such a powerful and effective technique, it is
always recommended that you insert your CG Infinity project files directly
into Video Editor (instead of rendering first and then inserting the resulting
AVI file) and use the Alpha Channel for the overlay.
VIDEO EDITOR: CHAPTER THREE
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