The short answer
Yes. You can pull a green screen out of a photo or a video without downloading a single app. Load the file into a browser-based keyer, tell it which color is the screen, and export a file that already has a transparent background. The whole thing runs in the page — the pixels are processed on your device and never uploaded anywhere, and there's no account to make.
How the cutout is decided
The tool looks at every pixel's color and measures how far it is from the screen color. Concretely it takes the Euclidean distance between that pixel's red, green, and blue values and the key color, then divides by 441.673 (that's √3 × 255) so the result lands on a 0–1 scale: 0 means "exactly the screen color" and 1 means "nothing like it." Pixels at or below the threshold become fully transparent; pixels well above it stay fully opaque; and there's a built-in 0.06 ramp between the two so the edge isn't a single hard line. One number — the key color plus the threshold — is doing all the work, and because only the alpha channel changes, the subject's own colors are left exactly as they were.
- Shrink erodes the kept area inward by a few pixels. That's what eats the thin green rim (spill) that clings to a subject on real footage.
- Smooth blurs the transparency edge by a few pixels so the silhouette looks less jagged.
Setting the key color
The default key is pure green (#00ff00). If your screen isn't green, switch to the blue preset or use the eyedropper: click the screen in the preview and the tool samples that exact pixel as the new key. The eyedropper is the most reliable choice for uneven lighting, since it grabs the actual color under the cursor rather than a fixed preset, and a closer key means fewer wrong pixels get removed.
Threshold: how much to take
Threshold is the similarity cutoff, shown as a percentage and starting at 18%. Lower it and only colors very close to the key disappear; raise it and a wider band of near-key colors is cut away. There's no single right value — it depends on how evenly the screen is lit and how close the subject's own colors sit to green. If part of your subject shares the screen color, keep the threshold low and let shrink clean the edge instead. If the background still isn't fully gone, nudge the threshold up a little and watch the preview. If the screen is lit unevenly, a single threshold may leave darker patches — raise it slightly and add a touch of smooth to disguise the seam.
Smoothing and shrinking
Begin from the defaults (shrink 2 px, smooth 4 px) and change one at a time. More shrink kills more halo but also eats into fine detail like hair; more smooth softens the outline but can fog a crisp edge. They pull in opposite directions, so tune by eye rather than maxing both.
Images versus video
For a still image the work is immediate: the page keys the image at its full resolution and shows a live preview while you drag the sliders, then you download one transparent PNG. The live preview is the reason image work feels instant. Image and video share the same algorithm and the same three sliders, so once you've tuned a look on a still you can apply the same numbers to the clip.
Video output: WebM or PNG frames
A transparent video needs a codec that can carry an alpha channel, which is why the tool records transparent WebM (VP9 first, then VP8) at 30 fps and 12 Mbps as the default. Because the WebM keeps its alpha, it composites cleanly over any background in a player that honors transparency. Not every browser can record alpha WebM through its media recorder, so when that path is unavailable it falls back to exporting a ZIP of individual transparent PNG frames — one PNG per frame — which any editor can reassemble. WebM is the single-file result; the PNG sequence is the universal fallback when alpha video isn't supported on your machine.
A quick workflow
- Open the page and drop in your file (image or video).
- Set the key color — green preset, blue preset, or eyedropper.
- Leave threshold at 18%, shrink at 2 px, smooth at 4 px to start.
- For video, pick WebM if your browser supports it, otherwise PNG frames.
- Process and download.
The steps above use a browser-based green screen keyer available at greenscreencut.com.
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