Green Screen Remover (Chroma Key)

Filmed in front of a green or blue screen? This tool removes the screen colour (chroma keying) and puts a new background behind your subject — a photo, another video or a plain colour — or saves the video with a transparent background for editing or for the web. It finds the exact shade of your screen by itself from the edges of the picture, softens the edges and removes the green tint that spills onto hair and skin. Check one frame first, then process the whole clip. It runs in your browser, so nothing is uploaded.

How to use this tool

1. Choose the green-screen video and, optionally, a background picture or video (otherwise a colour is used).
2. Keep "Find it automatically", or pick pure green, pure blue or a custom colour.
3. Look at the preview frame: raise the similarity if bits of the screen remain, lower it if parts of the subject disappear.
4. Choose the output, untick "Preview only" and run again; download the result.

Formula

A pixel becomes transparent when its colour distance to the screen colour is below the similarity; edge softness fades the pixels just above it

Keying is done on the colour part of each pixel (ffmpeg chromakey), so shadows on the screen key out as well as the lit parts. "Despill" pulls the green (or blue) reflected onto the subject back to neutral. A background picture or video is scaled to cover the frame and cropped; a shorter background video loops. Transparent WebM uses VP8 with an alpha channel; ProRes 4444 keeps full-quality alpha for editors but is very large — measured at about 1–1.6 bytes per pixel per frame, roughly 0.4–0.7 GB per minute at 640 × 360 and 4–6 GB per minute at 1080p (30 fps) — and the finished file must fit in the memory of the browser tab. The tool estimates 2 bytes per pixel and refuses anything over about 1.2 GB (300 MB on phones), which at 1080p and 30 fps is about 10 seconds.

Example

An evenly lit screen measured as #3c9a52 keys cleanly at similarity 0.12–0.18 with edge softness 0.05. A 30-second 1080p clip on a new photo background is re-encoded at roughly 2–3 frames per second in the browser, so it takes about 5–7 minutes; at 720p it is about twice as fast.