Digital chroma keying differs from its analogue equivalent in that it can key uniquely from any one of the 16 million colours represented in the component digital domain. It is then possible to key from relatively subdued colors, rather than relying on highly saturated colours that can cause colour spill problems on the foreground. A high-quality digital chroma keyer examines each of the three components of the picture and generates a linear key for each. These are then combined into a composite linear key for the final keying operation. The use of three keys allows much greater subtlety of selection than does a chrominance-only key.