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Chroma Key

Chroma Key · screenshot coming soon

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What this node does

Chroma Key removes a solid backdrop color (green screen, blue screen, or any custom color you pick) from a video and turns it into transparency or a matte. It works like a fast chroma keyer in After Effects or Premiere: pick the screen color, widen or tighten how much of that color is treated as “background”, soften the edge, and clean up the green/blue fringe (spill) that bleeds onto your subject. Input and output are COMFYTV_VIDEO. It has a ▶ Run — the key is computed by ffmpeg/PyAV, so processing happens when you run the node, not live.

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When to use it

  • You shot a person or product on a green/blue screen and want to drop them onto a new background.
  • You need a quick, reliable key without the extra controls of a full keyer.
  • You want a matte (grayscale mask) to feed a compositing or mixing step downstream.

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Parameters

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key_color

The backdrop color to remove, as a hex string. Default #00FF00 (pure green). Set it to your actual screen color — use #0000FF-ish for a blue screen, or sample the exact green from your footage for a cleaner key.

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similarity

How close a pixel’s color must be to key_color to count as background. Range 0.01–1.0, default 0.1. Raise it if parts of the screen are left behind; lower it if it starts eating into your subject.

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blend

Edge softness — how gradually pixels near the threshold fade from opaque to transparent. Range 0.0–1.0, default 0.05. A little blend gives a smoother, less jagged edge; too much makes the whole edge hazy.

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despill_mix

How strongly to remove the leftover screen color that reflects onto your subject (green/blue fringe on hair and edges). Range 0.0–1.0, default 0.5. Turn it up if edges look green; turn it down if skin tones go too gray.

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despill_expand

Grows the despill region outward from the keyed edge so more of the fringe is treated. Range 0.0–1.0, default 0.0. Nudge up when spill reaches beyond the immediate edge.

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output

What the node emits. alpha (default) produces a video with a real transparency channel; matte produces a grayscale mask (white = keep, black = remove). Note that alpha output needs a PyAV build with the VP9 encoder; if it errors, switch to matte.

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Outputs

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Tips

  • If alpha output fails with an encoder error, use matte and combine it downstream with Key Mix.
  • For difficult keys (uneven lighting, fine hair, motion blur) reach for PIK Keyer or Keyer, which expose finer controls.
  • To interoperate with native ComfyUI nodes, insert a Bridge. See bridges.md.
  • PIK Keyer — image-based (IBK-style) keyer with clean-plate and garbage-mask inputs for tougher shots.
  • Keyer — luma/chroma keyer with independent tolerance and softness on both sides.
  • Despill — dedicated spill suppression when you only need to clean fringe.
  • Key Mix — composite the keyed foreground over a new background using the matte.