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Lesson 4. Color and Opacity > Applying the Blue Screen opacity key

Applying the Blue Screen opacity key

The two most commonly used opacity keys are Blue Screen and Green Screen. These keys are generally used to substitute the background of one video clip with another. They are favored because they do not interfere with skin tones. For example, TV news programs regularly use blue screens to display footage of the current topic behind the newscaster.

If you use a blue or green background when videotaping footage and plan to key it out using the Blue or Green Screen key, make sure everything that is to remain opaque is a color other than your key color. For example, if you film a newscaster in front of a blue backdrop and the newscaster is wearing a blue tie, the tie will become transparent along with the background when you apply the Blue Screen key to the footage.

Blue Screen opacity with blue tie and with white tie

Now you'll add a clip to the Video 2 track and apply the Blue Screen key and the Chroma key.

In the Project window, double-click Sequence Ex to make it active in the Timeline.

Select the Color bin and choose File > Import. Select Storefront1.psd and click Open.

The Import Layered File dialog box appears. Select Choose Layer.

In the Choose Layer menu choose Bluescreen. Click OK.

Insert Bluescreen/Storefront1.psd at the beginning of the Video 2 track in the Timeline.

Make the duration equal to the duration of Opening.avi (00;00;06;05) by selecting Bluescreen/Storefront1.psd, choosing Clip > Speed/Duration, typing 605 in the duration field, and clicking OK.

Scrub in the Effect Controls window to see that Bluescreen/Storefront1.psd covers Opening.avi.

Go to the Effects palette and type blue in the Contains area. The Blue Screen Key effect appears. (Or, expand the Keying folder within the Video Effects folder and locate the Blue Screen Key effect.)

Select the Blue Screen Key effect and drag it to Bluescreen/Storefront1.psd in the Video 2 track of the Timeline window.

Click on Bluescreen/Storefront1.psd in the Timeline and then go to the Effect Controls window.

Click the triangle next to the Blue Screen Key effect to view its settings.

The Threshold and Cutoff sliders in the Effect Control palette alter the shadows and the extent of color selected and removed.

Scrub in the Effect Controls window, to see how much of the blue background has been keyed out.

Notice how the blue background carries over slightly. To enhance the appearance of the clip by removing all of this blue background, you'll adjust the Threshold slider.

Click in the box next to the Threshold area and type 83.0 or drag the Threshold slider to 83.0.

Notice how the background colors become saturated and more true. This is because you're removing more of the lingering blue value from the selected clip. You can see the effect in the Program view.

Preview the blue screen opacity effect by using Real-Time playback or by scrubbing through the Timeline.

Save the project.

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