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# About the Keyer

Use the Keyer to make parts of an image transparent by selecting and isolating regions of colour. This process creates an alpha-channel matte, which is then used to composite the image over a new background.

You can create composites by defining transparent regions in a foreground clip, based on a specific range of colour, to reveal a background clip. This keying process is usually performed on footage with a subject in front of a blue or green screen. When you key out a colour, you generate a matte: a black and white template indicating which parts of the image are transparent (black), and which are opaque (white). Using techniques such as softening the edge of mattes, you can refine the results to create realistic composites.

You can also use garbage masks to key out undesired elements in an image. To learn about using garbage masks when pulling a key, see About Garbage Masks.