You can also use the Luma key to key out light areas by setting Threshold to a low
value and Cutoff to a high value.
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Using the Multiply and Screen keys
The Multiply and Screen keys use an underlying image as a map to determine what part of
the keyed image to make transparent. The Multiply key creates transparency in the areas
of the image that correspond to the bright areas in the underlying image. Conversely, the
Screen key creates transparency in the areas that correspond to the dark areas of the
underlying image. Like the Luma key, the Multiply and Screen keys are most effective
when the image that you are keying contains highly contrasting dark and light areas.
Use these keys to create a subtle superimposition, when the underlying image contains
highly contrasting elements.
Adjust the following settings as necessary:
Opacity
Drag to the right until the opacity of the effect reaches a satisfactory level.
Higher values produce less transparency.
Cutoff
Drag to the right until the opaque area reaches a satisfactory level. Higher values
produce less transparency.
Using matte keys
A matte is a specified still image that you use to determine where to apply an effect to a
clip. You can use matte keys to add traveling mattes or creative superimpositions.
Using the Image Matte key
The Image Matte key determines the areas of transparency for a clip by using a matte
image’s alpha channel or brightness values. To get the most predictable results, 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 appear
blue-green (since white in an RGB image is composed of 100% red, 100% blue, and 100%
green); because red also becomes transparent in the clip, only blue and green colors
remain at their original values.
Adjust the following Image Matte settings as necessary:
Setup
Click to select an image. Portions of the clip in the track that correspond to the
white areas of the image are superimposed on clips in lower tracks.
Composite Using
Select Matte Alpha to composite using the values in the alpha channel
of the image you selected using the Setup button. Select Matte Luma to composite using
the image’s luminance values instead.
Reverse Key
Click to reverse transparency. Portions of the clip in the track that
correspond
to the black areas of the image are superimposed on clips in lower tracks.
Using the Difference Matte key
The Difference Matte key 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.
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In this way, you can replace a static background behind a moving object (such as a person
walking past a stage set). Very often the specified image is simply a frame of background
