Extract Alpha ·

A Claude Code plugin that removes backgrounds from AI-generated images using two-pass difference matting.

The Problem

AI image generators (Gemini, DALL-E, Midjourney, etc.) often don't support transparent backgrounds. You get a PNG with a solid white or black background baked in.

The Solution

Generate the same image twice — once on white, once on black. The difference between the two reveals the exact transparency of every pixel:

• Fully opaque pixels look identical on both backgrounds
• Fully transparent pixels show pure white vs pure black
• Semi-transparent pixels show proportional differences

Math: alpha = 1 - colorDistance(whiteImg, blackImg) / maxDistance

This produces pixel-perfect alpha extraction — no AI guessing, no edge artifacts.

Quick Install

/install furic/extract-alpha

That's it — the plugin installs both skills automatically.

Manual Install

If you prefer to install manually:

git clone https://github.com/furic/extract-alpha.git
mkdir -p ~/.claude/skills/extract-alpha
cp extract-alpha/skills/extract/SKILL.md ~/.claude/skills/extract-alpha/SKILL.md

Requirements

• Python 3 with Pillow installed (pip install Pillow)

Skills

This plugin provides two skills:

/extract-alpha:extract — Extract transparency

Processes a white/black background image pair and outputs a transparent PNG.

/extract-alpha:extract path/to/image_white.png

Accepts any of these file path forms:

• {name}_white.png — automatically finds the matching {name}_black.png
• {name}_black.png — automatically finds the matching {name}_white.png
• {name}.png — looks for both {name}_white.png and {name}_black.png

Output: {name}.png with full transparency, saved alongside the input files.

/extract-alpha:prompt — Generate image prompts

Generates a pair of AI image prompts (white + black background) ready for alpha extraction.

/extract-alpha:prompt a dragon logo for my fantasy game

This outputs two ready-to-use prompts:

1. Prompt 1 — A detailed image generation prompt with a white background
2. Prompt 2 — A follow-up prompt to swap to black background

Workflow

Option A: Use the prompt skill (recommended)

1. Run /extract-alpha:prompt <description> to generate the prompt pair
2. Send Prompt 1 to your AI image generator (Gemini, ChatGPT, etc.)
3. Save the result as {name}_white.png
4. In the same conversation, send Prompt 2
5. Save the result as {name}_black.png
6. Run /extract-alpha:extract {name}_white.png

Option B: Write prompts manually

Add this line at the end of your image prompt:

- On a pure solid white #FFFFFF background

Then send a follow-up in the same conversation:

Change the white background to a solid pure black #000000. Keep everything else exactly unchanged.

Save the results as {name}_white.png and {name}_black.png, then run /extract-alpha:extract.

Why the same conversation? The AI retains context about the exact image it just created, so only the background changes. Generating two separate images from scratch produces inconsistent results.

How It Works

1. Load both white-background and black-background images
2. For each pixel, calculate the color distance between the two versions
3. Derive alpha: alpha = 1 - distance / maxDistance
4. Recover original RGB: rgb = blackImg_rgb / alpha
5. Output RGBA image with extracted transparency

The script handles minor size differences between images (common with AI generators) by cropping to the smaller dimensions.

License

MIT