How chroma keying works

Chroma keying (commonly called "green screen") works by identifying pixels in the video frame that are close in color to the selected key color, then replacing those pixels with a background color or image. The threshold control determines how strict or lenient the color matching is.

Tips for a clean key

Use a uniform, well-lit background - shadows and wrinkles create color variation.
Keep the subject away from the background to avoid color spill.
Start with a low threshold and increase it gradually until fringing is minimised.

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Background color choices: green vs. blue

Green is the dominant choice for modern chroma key work because:

Green is the rarest color in human skin tones and hair, minimizing the risk of accidentally keying out parts of the subject.
Digital camera sensors have twice as many green photosites as red or blue (Bayer pattern), making the green channel the cleanest and easiest to key.
Green reflects more light than blue, requiring less lighting power.

Blue screen is preferred when the subject is wearing green, or in certain film contexts where the blue channel is cleaner for specific film stocks or lighting setups. Blue also blends better with the natural sky in outdoor compositing.

Spill suppression

Color spill occurs when green or blue light reflects off the background screen and tints the edges of the subject. It appears as a green halo around hair, shoulders, or translucent clothing. To minimize spill:

Keep the subject as far from the background as possible (2–3 meters minimum).
Avoid tight backgrounds with insufficient lighting - even lighting prevents hot spots.
In post-processing, spill suppression algorithms shift the affected edge pixels toward their complementary color (adding magenta for green spill).

Common mistakes

Uneven lighting: shadows and highlights on the background create different shades of green, making a single color threshold insufficient. Aim for flat, even lighting across the entire background.
Wrinkled background: wrinkles create shadows and uneven color. Stretch the screen taut or use a painted wall or a ring-lit curved backdrop.
Subject too close to background: increases spill and makes it harder to light the subject independently of the background.