Grass Valley Indigo AV Mixer v.1.2.2 - Manual (Page 54)

54 INDIGO AV Mixer User Manual
Section 5 — Basic Operation
The terms foreground and background are often a source of confusion
when used for chroma keys. Foreground refers to the people or objects in
a chroma key scene that are in front of the colored backdrop. Background
refers to the scene that will replace the backing color (same as a linear or
luminance key) in the final picture. Background does not refer to the back-
drop of the foreground scene.
Chroma keys are performed by suppressing the backing color in the fore-
ground scene, cutting a hole in the background, and then combining the
two processed signals. When conditions are ideal, complete suppression
of the backing color is possible and the hole cut in the background will
match the suppressed foreground, permitting these two signals to be
added successfully.