Screen Print Color Separator

Made for Ryley

A minimal web app to convert a logo/image into screen print-ready color separations. Upload an image and the app will:

• Auto-detect the number of colors using an elbow method in a LAB-like color space
• Generate per-color plates with cleaned/dilated masks for films
• Generate an optional underbase with adjustable spread
• Provide colorized previews and original-color layers
• Package everything into a ZIP with a manifest and a composite that matches the source

Features

• Automatic color count (up to 8)
• Perceptual clustering (LAB-like transform, k-means)
• Cleaned print plates: min-area removal and optional dilation
• Underbase generation with adjustable spread
• Original-color layers to reconstruct the exact image
• Colorized layers for quick review
• Single-click ZIP download with organized folders

How it works

1. The image is converted to RGBA and sampled in a LAB-like color space
2. The optimal number of colors is estimated via an elbow method on SSE vs K
3. K-means clusters the sampled points, then the full image is labeled by nearest cluster
4. Two sets of masks are produced:
   • Raw masks: used to slice original per-pixel color layers (perfect visual composite)
   • Production masks: optional cleanup (min-area), and dilation for registration/bleed
5. Exports:
   • layers_original/: original per-pixel RGBA per cluster (stacks to the exact original)
   • layers_color/: flat color per cluster for visual reference
   • plates_black/: opaque black plates for film positives
   • underbase/: white and black variants (optional)
   • composite.png: layers_original composited server-side (reference)

Output ZIP structure

• layers_original/
• layers_color/
• plates_black/
• underbase/ (optional)
• composite.png
• README.txt

Requirements

• Python 3.10+

Install dependencies:

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Run locally

export PORT=5050
python app.py
# Open http://localhost:5050

Usage

• Upload PNG/JPG/WebP
• Options:
  • Plate expand px: dilates production masks for registration tolerance
  • Min area (px): removes tiny specks from production masks
  • Underbase: adds a solid underbase with configurable spread
• Press Process and download the ZIP

Photoshop recomposite

• Import all images from layers_original/ as layers
• Blend mode Normal, opacity 100%, order as-is
• Ensure sRGB workflow without profile conversion
• Result should match composite.png and the original

Notes for screen printing

• Use plates_black/ for film positives
• layers_color/ previews assist visual checks and spot-color naming
• underbase/ gives both white and black variants; adjust spread based on garment and ink
• If your artwork includes gradients/anti-aliasing, keep layers_original/ for reference and use halftones when burning screens

Limitations

• Clustering is unsupervised; complex photos may separate into more plates than ideal
• The LAB-like transform is an approximation to avoid heavy native dependencies
• No RIP/halftone generation; use your shop’s RIP settings

Security

• Uploads are processed in-memory and written under runs/<uuid>/
• runs/ is ignored by git and not intended for permanent storage

License

MIT