To add practical fire, explosions, smoke or other footage not containing an Alpha channel is normally a challenge. A normal Math Composite Add function would cause areas of the background to get brighter. This is bad. Using a key of some type would most likely generate unwanted edge fringing. This is also bad. The Holdout Composite is a two-layer/track effect that effectively composites images such as fire, explosions and smoke. This plug-in first creates a luminance matte of the foreground and pastes it as black (or other color) over the background. You then use one of the Blend Modes to place the foreground over the “held out background”.