A matte is an image used to define or control the transparency of another image. When you pull a key, you generate a matte that defines the transparency of the front source. There are several types of mattes.

Articulate matte A matte whose shape changes over time and is designed to accurately follow the contours of the object to which it corresponds.

Complementary matte The matte that results when the primary matte is inverted.

Difference matte A matte created by subtracting an image in which the subject is present from an otherwise identical image in which the subject is not present.

Edge matte A matte that includes only the outlines or borders of an object.

Fixed or static matte A matte that does not change position or shape over time.

Garbage matte A matte that isolates unwanted elements from the primary element in an image. Garbage mattes are also referred to as garbage masks.

Hold-out matte A matte that prevents a foreground element from completely obscuring an object in the background.

Traveling matte A matte that changes position or shape over time.