Image Region Remove Key Color App

Image Region Remove Key Color App

Paint a region mask in a local Gradio UI, then remove key-color pixels only inside that region (global keying scoped to the brush). Preserves white/light subject pixels outside the paint strokes.

Use after [image-remove-white-background](../image-remove-white-background/SKILL.md) when edge flood fill leaves enclosed white islands (e.g. gaps inside a silhouette).

Rules

When this skill applies, read and follow [skill-dependency-manager](../../rules/skill-dependency-manager.md) — run scripts as documented, install missing tools into .dependency/.

• Run app.py through the image-region-remove-key-color-app manifest entry (.dependency/image-region-remove-key-color-app/.venv/). Never use host python, py, python3, or any interpreter outside .dependency/.
• Do not hand-write a one-off Gradio app — use the bundled script.
• populated: false is not a reason to skip. Install first, set populated: true, retry the same command.
• This skill is interactive: launch the UI, give the user the local URL, wait for them to paint / Apply / Download.

Setup (first run)

From project root:

.dependency/python/python -m venv .dependency/image-region-remove-key-color-app/.venv
.dependency/image-region-remove-key-color-app/.venv/Scripts/python -m pip install Pillow gradio

If python -m venv fails (missing venv / ensurepip), create the env with virtualenv from another populated skill venv, then install packages into the new env:

.dependency/rembg/.venv/Scripts/python -m pip install virtualenv
.dependency/rembg/.venv/Scripts/python -m virtualenv .dependency/image-region-remove-key-color-app/.venv
.dependency/image-region-remove-key-color-app/.venv/Scripts/python -m pip install Pillow gradio

Register in .dependency/manifest.json:

"image-region-remove-key-color-app": {
  "populated": true,
  "bin": ".dependency/image-region-remove-key-color-app/.venv/Scripts/python.exe"
}

Use bin/python on Unix.

Quick Start

# Preload an image (opens http://127.0.0.1:7860)
.dependency/image-region-remove-key-color-app/.venv/Scripts/python \
  .cursor/skills/image-region-remove-key-color-app/scripts/app.py \
  path/to/sprite.png

# Custom port
.dependency/image-region-remove-key-color-app/.venv/Scripts/python \
  .cursor/skills/image-region-remove-key-color-app/scripts/app.py \
  path/to/sprite.png \
  --port 7861

Download uses the same filename as the source (forced .png). No share / no save-to-disk folder.

UI workflow

1. Upload the image via the file control (or preload via CLI) — do not drop into the editor canvas.
2. Transparent areas appear as gray in the editor (download still has real alpha).
3. Paint over local white / chroma patches to remove.
4. Choose Key color / tolerance / feather if needed.
5. Click Apply → preview (gray = transparent).
6. Click Download → browser download with the original name.
7. Click Stop server when done (or Ctrl+C in the terminal).

Key color

Use the UI color picker (default #FFFFFF). CLI --preset only sets the initial color and tolerance:

| --preset | Key color | Default tolerance | |------------|-----------|-------------------| | white (default) | #FFFFFF | 25 | | green | #00FF00 | 40 | | magenta | #FF00FF | 40 |

Agent workflow

1. When — user needs selective / painted removal of flat key-color patches; full-image global would damage white subjects; border/both left enclosed islands.
2. Ensure deps — manifest entry + venv with Pillow + Gradio.
3. Launch — run app.py with the user image path; prefer --no-browser if the agent cannot open a GUI browser, and print http://127.0.0.1:.
4. Hand off — tell the user to paint, Apply, then Download (same filename as source).
5. Verify — after the user confirms download, they are done; do not overwrite sources.
6. Stop — click Stop server in the UI, or terminate the Gradio process when the user is done.

Defaults

| Option | Default | Notes | |--------|---------|-------| | Download name | same as source (.png) | Prepared on Apply via DownloadButton | | --preset | white | Match the batch key skill | | --tolerance | preset-specific | Raise for gray fringes | | --feather | 2 | Softens hole edges inside the paint mask | | --port | 7860 | Change if busy | | Share | off | share=False; no share UI |

Troubleshooting

| Issue | Fix | |-------|-----| | Manifest / venv missing | Follow Setup; update manifest | | No paint strokes found | Brush visibly over the white islands; ensure strokes are on the editor layers | | Subject holes outside paint | Only paint the background islands — strokes gate keying | | Leftover fringe in region | Raise tolerance by 5–10 | | Port in use | Pass --port 7861 (etc.) | | Gradio import error | Reinstall in the skill venv: pip install -U Pillow gradio |

Related

• Full-image / batch keying: [image-remove-white-background](../image-remove-white-background/SKILL.md)
• AI matting: [image-remove-background](../image-remove-background/SKILL.md)

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: godot-fun
• Source: godot-fun/godot-framework
• License: MIT

Install and usage instructions live in the source repository linked above.