> ## Documentation Index
> Fetch the complete documentation index at: https://comfytv.org/llms.txt
> Use this file to discover all available pages before exploring further.
# Chroma Key
> Pull a green- or blue-screen key out of a clip with built-in spill suppression, in one pass.
## 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.
## 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.
## Parameters
### 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.
### 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.
### 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.
### 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.
### 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.
### 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`.
## Outputs
| Output | Type | Meaning |
| --------- | --------------- | ------------------------------------------------------------------- |
| **video** | `COMFYTV_VIDEO` | The keyed clip: transparent (`alpha`) or grayscale matte (`matte`). |
## 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](https://github.com/jtydhr88/ComfyTV/blob/main/docs/bridges.md).
## Related nodes
* **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.