Keying (chroma key / luma key) / 去背／鍵控 — theatre and live events glossary

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Keying (chroma key / luma key) 去背／鍵控

video

Making part of an image transparent so another source shows through it. Chroma key removes a specific colour — green or blue screen. Luma key removes a brightness range instead, which is why it still works on footage with no coloured screen at all: titles on black, or pulling a bright practical light through a layer.

中文

將畫面的一部分變成透明，讓另一個訊號透出。色鍵（chroma key）看顏色，亮度鍵（luma key）看亮度。

Easy to get wrong

Calling for "a key" on comms doesn't say which technique. If the background isn't a clean solid colour, chroma key won't pull it — you need luma key or a different composite instead.

Sources

Chroma key — Wikipedia primary
A Glossary of Live Production Buzzwords — B&H Photo Video / eXplora
Video Post-Production Workflow Guide: Keying — Frame.io

Understand the mechanism

Node graphs and game engines How it all runs together

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