Adobe PREMIERE 5 User Manual page 278

270 CHAPTER 8
Superimposing and Compositing with Transparency
To get the most predictable results, you should choose a grayscale image for your image matte,
unless you want to alter colors in the clip. Any color in the image matte removes the same level
of color from the clip you are keying. For example, white areas in the clip that correspond to
red areas in the image matte will appear blue-green (since white in an RGB image is composed
of 100% red, 100% blue and 100% green); because red is also made transparent in the clip, only
blue and green colors would remain at their original values.
Choose
to the white areas of the image are superimposed on clips in lower tracks.The image acts as a
filter between the clips.
Reverse Key
correspond to the black areas of the image are superimposed on clips in lower tracks.
Difference Matte
The Difference Matte creates transparency by comparing a specified image with a specified clip
and then eliminating areas in the clip that match those in the image. Though you can use this
key to create special effects, you can also use it to key out a static background by selecting the
Reverse Key option.
In this way, you can remove a static background behind a moving object (such as a person
walking past a stage set), and place the person against a different background. Very often the
specified image is simply a frame of background footage (before the moving object has entered
the scene). For this reason, the Difference Matte is best used in this way for scenes that have
been shot with a stationary camera.
To replace a static background behind a moving object:
1 Find a frame of your clip that consists only of the static background.
2 Save this background frame as an image file. For information about saving a frame,
see "Exporting a still image" on page 328.
3 Place the video clip in a superimpose track, select it, and then choose Clip > Video >
Transparency.
For Key Type, choose Difference Matte.
4
Click to select an image. Portions of the clip in the superimpose track that correspond
Click to reverse transparency. Portions of the clip in the superimpose track that