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Chapter 13. Super-imposing Clips > Using the Chroma Key

Using the Chroma Key

All the chrominance-based keys work essentially the same way, although the chroma key is the most flexible.

To use the chroma key:

1.
Select a clip in a superimpose track, and choose Clip > Video Options > Transparency (Figure 13.33).

Figure 13.33. Select a clip in a superimpose track, and choose Clip > Video Options > Transparency.


The Transparency Settings dialog box appears.

2.
From the Key Type pull-down menu of the Transparency Settings dialog box, choose Chroma (Figure 13.34).

Figure 13.34. Choose Chroma from the Key Type pull-down menu.


3.
In the Color section of the Transparency Settings dialog box, choose a key color by doing either of the following:

  • To select a color from the thumbnail image, click in the thumbnail image.

    The eyedropper tool appears, and the selected color appears in the color swatch above the thumbnail (Figure 13.35).

    Figure 13.35. Choose a key color by clicking in the thumbnail image (shown here) or open the color picker by clicking the color swatch.

  • To choose a color from the color picker, click the color swatch over the thumbnail image.

The color picker appears. Select a color and click OK to set the key color and return to the Transparency Settings dialog box.

4.
To adjust the key, drag the sliders:

Similarity—to increase or decrease the range of colors similar to the key color that are keyed out.

Blend—to blend the clip with the underlying clip.

Threshold—to control the amount of shadows that you keep in the range of key colors.

Cutoff—to darken or lighten shadows.

Don't drag the Cutoff beyond the Threshold, or you will invert the gray and transparent pixels.

Smoothing—to antialias (smooth) the edges of the opaque areas.

5.
Preview the effects of your adjustments in the sample frame (Figure 13.36).

Figure 13.36. Adjust the key with the slider controls, and preview the effect in the sample frame.


6.
When you are satisfied with the adjustments, click OK to close the Transparency Settings dialog box and apply the settings.


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