Color Difference Key (PB only)

This Key creates transparency from opposite starting points by dividing an image into two mattes, Matte Partial A and Matte Partial B. Matte Partial B bases the transparency on the specified key color, and Matte Partial A bases transparency on areas of the image that do not contain a second, different color. By combining the two mattes into a third matte, called the alpha() matte, the Color Difference Key creates well-defined transparency values.

The Color Difference Key produces high-quality keying for all well-lit footage items shot against a bluescreen or greenscreen and works especially well with images that contain transparent or semitransparent areas, such as smoke, shadows, or glass.


A. Original image thumbnail B. White eyedropper C. Matte controls D. Thumbnail eyedropper E. Black eyedropper F. Matte thumbnail G. Matte buttons H. View I. Key Color swatch and eyedropper J. Color Matching Accuracy

To apply the Color Difference Key:

1. Select the layer you want to make transparent, and then choose Effect > Keying > Color Difference Key.
2. In the Effect Controls window, choose Matte Corrected from the View menu. To view and compare the source image, both partial mattes, and the final matte at the same time, choose [A, B, Matte] Corrected, Final from the View menu. Other views available in the View menu are described in step 10.
3. Select the appropriate key color in one of the following ways:
• To key out a bluescreen, use the default blue color.
• To key out a non-bluescreen, select a key color in one of the following ways:

Thumbnail eyedropper

Select and then click in the Composition window or the original image thumbnail on an appropriate area.

Key Color eyedropper

Select and then click in the Composition or Layer window on an appropriate area.

Key Color swatch

Click to select a color from the specified color space.

Note: The eyedropper tools move the sliders accordingly. Use the sliders in step 9 to fine-tune the keying results.

4. Click the matte button to display the final combined matte in the matte thumbnail.
5. Select the Black eyedropper, and then click inside the matte thumbnail on the lightest area of black to specify transparent regions. The transparency values in the thumbnail and Composition window are adjusted.

6. Select the White eyedropper, and then click inside the matte thumbnail on the darkest area of white to specify opaque regions. The opaque values in the thumbnail and the Composition window are adjusted.


To produce the best possible key, make the black and white areas as different as you can so that the image retains as many shades of gray as possible.

7. Select a matching accuracy from the Color Matching Accuracy menu. Choose Faster unless you are using a screen that is not a primary color, such as orange. For those screens, choose More Accurate, which increases rendering time but produces better results.
8. If you need to further adjust transparency values, repeat steps 5 and 6 for one or both of the partial mattes. Click the Partial Matte B button or the Partial Matte A button to select a partial matte, and then repeat the steps.
9. Adjust transparency values for each partial matte and for the final matte by dragging one or more of the following slider bars in the Matte Controls section:
• Black slider bars adjust the transparency levels of each matte. You can adjust the same levels using the Black eyedropper.
• White slider bars adjust the opaque levels of each matte. You can adjust the same levels using the White eyedropper.
• Gamma slider bars control how closely the transparency values follow a linear progression. At a value of 1 (the default), the progression is linear. Other values produce nonlinear progressions for particular adjustments or visual effects.
10. When adjusting individual mattes, you can choose the following views from the View menu to compare the mattes with and without adjustments:
• Choose Uncorrected to view a matte without adjustments made by the slider bars in step 9.
• Choose Corrected to view a matte with all adjustments made by the slider bars in step 9.
11. Before closing the Effect Controls window, select Final Output from the View menu. Final Output must be selected for After Effects to render the transparency.

To remove traces of reflected key color from the image, apply Spill Suppressor using Better for Color Accuracy. If the image still has a lot of color, apply the Simple Choker or Matte Choker matte tool. For more information, see Simple Choker (PB only) or Matte Choker (PB only).