Workshop

Review the questions and answers in this section to try to sharpen your Premiere alpha channel and matte compositing skills. Also, take a few moments to tackle my short quiz and the exercises.

Q&A

Q1:	I want to use the QuickTime Cloud and Fire effects on a clip, but when I apply them to the clip all I see is the effect. My clip disappears. What's up?
A1:	The QuickTime Cloud and Fire video effects create their own animated clip. Basically whatever clip you apply them to merely tells these effects how long to run. To use them with a clip, you need to apply them to a separate clip. It can be any clip, but to simplify things, create a color matte and apply the effects to it. That clip needs to be on a superimposing video track above the background clip on the timeline.
Q2:	I tried using the difference matte but when I move the Similarity slider, my actor disappears, not the background scene. Why?
A2:	The difference matte is an odd duck. It looks for differences between two images and removes them. But that's not what you want to do. You want to remove similarities . Therefore, check the Reverse Key box to do just that.

Quiz

1:	When would you use a black or white alpha matte instead of an alpha channel transparency?
A1:	Most graphic images with alpha channels have straight alpha channels. When you use Alpha Channel Transparency on them, the edges of the graphics will be sharply detailed. Use black or white alpha mattes for graphics with premultiplied alpha channels ”black for graphics with black backgrounds; white for white backgrounds.
2:	If black areas of an alpha channel are transparent, why is black text on a graphic with an alpha channel opaque ?
A2:	The color of the graphic does not set opacity. The color of the alpha channel does. Typically artists create graphics and build an alpha channel stencil to match the graphic's borders. In that alpha channel layer, areas beneath the graphic are white to ensure the graphic remains opaque no matter what color it is.
3:	What's the difference between an image matte and a track matte?
A3:	You apply an image matte directly to a clip by opening that clip's Transparency Settings dialog box, selecting Image Matte, and choosing a matte. Using a track matte is sort of an indirect process. You place it on a video track directly above the clip to which you want to apply it. Then you open that clip's Transparency Settings dialog box and select Track Matte. You don't need to choose the matte because Premiere knows you're referring to whatever image is on the next higher track. You use track mattes to create traveling or moving mattes.

Exercises

1:	Create a four-segment split screen. That means making three mattes with black covering three- quarters of each one. Then place the same person/object in each quadrant of the same scene.
2:	Create a track/traveling matte that actually follows action. You'll need to make a matte with a simple shape ”a black rectangle for instance. Put a clip with something moving through it on Video 1 and a color matte on Video 2. Place the matte on Video 3. Apply a track matte transparency to the Video 2 clip. Apply motion to the matte on Video 3. You'll need to view the clip in the Motion Settings preview window and add keyframes using the Motion Settings timeline. I'll go over this in detail in Hour 16. Good luck.
3:	Tape a clear blue sky and then use the QuickTime Cloud video effect several times to add multiple clouds to it. Give each cloud motion to have them all move through the scene with the semblance of coordinated behavior.