The Chroma Key effect specifies which color or range of colors in the clip becomes transparent. You can use this key for a scene shot against a monochromatic screen, such as a blue or green screen.

The following Chroma Key settings are adjusted in the Effect Controls panel:

Similarity

Broadens or reduces the range of the target color that will be made transparent. Higher values increase the range.

Blend

Blends the clip you are keying out with the underlying clip. Higher values blend more of the clip.

Threshold

Controls the amount of shadows in the range of color you keyed out. Higher values retain more shadows.

Cutoff

Darkens or lightens shadows. Drag to the right to darken shadows, but do not drag beyond the Threshold slider; doing so inverts gray and transparent pixels.

Smoothing

Specifies the amount of anti-aliasing that Adobe Premiere Pro applies to the boundary between transparent and opaque regions. Anti-aliasing blends pixels to produce softer, smoother edges. Choose None to produce sharp edges, with no anti-aliasing. This option is useful when you want to preserve sharp lines, such as those in titles. Choose Low or High to produce different amounts of smoothing.

Mask Only

Displays only the clip’s alpha channel. Black represents transparent areas, white represents opaque areas, and gray represents partially transparent areas.