What is Chroma Key?
Chroma key isolates pixels within a selected color range, commonly green or blue, and makes that region transparent. Another image or video layer can then replace the removed background.
How Chroma Key works
A keyer converts a chosen background color into a matte whose values control the opacity of the foreground. Production keying usually combines color-distance selection with edge refinement, hole filling, noise cleanup, and spill suppression rather than applying a single exact-color comparison. The matte then enters a compositing stage, where foreground and replacement imagery must share suitable color, resolution, and alpha conventions to avoid visible seams.
Key facts
- Threshold and softness settings trade background removal against foreground retention; hair, motion blur, reflections, and translucent materials often require partial matte values rather than binary opacity.
- Lossy compression and 4:2:0 sampling reduce color detail around edges, so heavily compressed delivery footage generally yields a rougher key than a less compressed, higher-chroma source.
- Despill changes green or blue contamination on foreground edges without defining transparency. Applying it too aggressively can neutralize legitimate object colors and create gray outlines.
When Chroma Key matters
Use chroma key to automate virtual backgrounds, studio composites, or layered video effects. Uneven lighting, color spill, and foreground colors close to the key color can produce visible failures.