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Using the Keylight filter in After Effects

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Table of Contents

  1. Introduction
  2. Using the Keylight filter
  • PDF Version

    • Using the Keylight filter

    Follow these steps to create an alpha channel video using the Keylight filter:

    1. Open the GS_02.aep file in the Zip file at the top of this tutorial. When the file opens, open the Effects & Presets panel, twirl down the Keying category, and drag a copy of the Keylight filter onto the Comp. When you release the mouse, the Keylight controls—shown in Figure 1—will appear in the Effect Controls panel. If you examine them, the first thing that will occur to you is that all of the filters and controls used in the previous exercise are in the panel. We told you this filter was industrial strength!

       

      The Keylight filter

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      Figure 1: The Keylight filter is applied to the video in the Comp window, and the controls are ready to be used.

      Note: Another way of applying the filter is to click the Comp and then select Effect > Keying > Keylight.

    2. Click the eyedropper and click the green background. The first thing you will notice is all the green disappears. If you toggle the transparency, you will see that the green is essentially gone. Unfortunately, it would be a huge mistake on your part to think “My job is done.” Not quite. If you select Status from the View pull-down, you will see there is still a lot of work that needs to be done. The Status view, much like in Adobe® Photoshop®, shows you the mask. There is still a lot of gray in the Comp. The view should only have two colors: the subject should be pure white and the background should be pure black. Return to the Final Result view.
    3. Twirl down the Screen Pre Blur control and set the Pre Blur value to 2. What this control does is to blur the matte. If you use DV footage, the pixels in the image can be rather blocky, and this control tends to give you a much smoother edge before you “pull” the key. You can see the effect by selecting the Combined Matte view and dragging the slider.
    4. The next step in the process is to deal with those gray pixels you saw earlier. Switch to the Screen Matte view and twirl down the Screen Matte control. The controls you will be using are the Clip Black and Clip White controls. The Clip Black control functions very much like the Magic Wand tool in Photoshop and Fireworks. Moving the slider to the right increases the tolerance value and increases the size of the area covered in black pixels. Drag the Clip Black slider to a value of about 35. You will notice, as you drag this slider, a few gray artifacts appear in the white area of the mask. Twirl down the Clip White control and drag the slider to a value of 56. The gray pixels in the white, as shown in Figure 2, have disappeared, and you have a solid black-and-white mask.

       

      the mask

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      Figure 2: The mask is looking pretty good.

    5. The next step is to shrink the mask a bit to ensure you don’t have an odd-looking edge around the key. Twirl down the Screen Shrink/Grow control and set the value to -.5 to shrink the mask. You don’t need a big value here. Remember, finesse is what counts when keying, not brute force.
    6. The final step is to deal with the spill. The neat thing about Keylight is that it does manage this for you as you are working. It will find the spill and replace it with a default gray color. To see this at work, change the view to Intermediate Result and zoom in on an edge. You will see the spill. Change the view back to Final Result, and you will see the green is replaced with the gray. To refine this even more, twirl down the Screen Despot White control and change Replace Method to Hard Color. The result of this will be a softer blend of the green color being replaced.
    7. Click in the Screen Despot White Color chip to open the Color Picker. Choose a green from the hue bar and when the color appears in the Color Picker, choose a green that is somewhere between full green and gray (see Figure 3).

       

      spill suppression

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      Figure 3: Dealing with spill suppression.

    8. Save the project.

    Where to go from here

    For more information about working with After Effects and Flash, check out the following articles:

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