Chroma Key

Chroma keying isolates a foreground subject by identifying a uniform background color (typically green or blue) and making it transparent. The keyer calculates the difference between the screen color and the foreground pixels, generating a matte that determines opacity per pixel. In After Effects, Keylight (built-in, developed by The Foundry) is the standard. A practical starting configuration: set Screen Colour by eyedroppering the most representative green area, then adjust Screen Balance to 70% (the default 100% often over-suppresses), and edge feathering between 1.5–3 pixels to soften the matte boundary without losing fine detail. For hair and transparency, switch the View to Intermediate Result and tune the Screen Matte > Clip Black to ~15 and Clip White to ~70 as a baseline — these values choke the matte to eliminate noise in transparent areas while preserving semi-transparent strands.

Green screens are standard because camera sensors have twice as many green photosites as red or blue in the Bayer pattern, giving the highest chroma resolution on the green channel. But green produces more spill on fair skin and blonde hair — the reflected green light contaminates edges in ways that are difficult to correct without destroying skin tone accuracy. Blue screen works better for blonde hair because the blue channel has less natural overlap with warm skin tones, making spill suppression less destructive. DaVinci Resolve offers two primary keyers: the Delta Keyer (built into the Color page, uses a 3D color difference algorithm) and the 3D Keyer (found in Fusion, samples a 3D color volume). For fine hair detail, the Delta Keyer's Softness and Cleanup parameters give more control over edge quality than the 3D Keyer's global tolerance slider. The hard constraint: H.264 4:2:0 footage contains only half the chroma resolution of the luma channel. This means the keyer is working with interpolated color data at the edges. No keyer, no matter how advanced, can extract clean hair edges from footage that does not have the chroma information to begin with. Shoot 4:2:2 (ProRes) or 4:4:4 (RAW) if your project involves compositing.