ulpi-io Image Processing
Process images for web development. Generate a Pillow script adapted to the user's environment and specific needs.
Prerequisites
Pillow is usually pre-installed. If not:
pip install Pillow
If Pillow is unavailable, adapt using alternatives:
| Alternative | Platform | Install | Capabilities |
|---|---|---|---|
sips |
macOS (built-in) | None | Resize, convert (no trim/OG) |
sharp |
Node.js | npm install sharp |
Full feature set |
ffmpeg |
Cross-platform | brew install ffmpeg |
Resize, convert |
Capabilities
Generate a Python script using Pillow for any of these operations. See references/pillow-patterns.md for implementation patterns, especially RGBA-to-JPG compositing and cross-platform font discovery.
Resize
Scale to specific dimensions or by width/height (maintain aspect ratio if only one given). Use Image.LANCZOS for high-quality downscaling.
Convert Format
Convert between PNG, JPG, WebP. Handle RGBA-to-JPG by compositing onto white background. Apply format-specific quality settings (WebP: 85, JPG: 90, PNG: optimize).
Trim Whitespace
Auto-crop surrounding whitespace from logos and icons. Convert to RGBA first, then use getbbox() to find content bounds.
Thumbnail
Fit within max dimensions while maintaining aspect ratio. Use img.thumbnail((size, size), Image.LANCZOS).
Optimise for Web
Resize + compress in one step. Convert to WebP for best compression. Typical settings: width 1920, quality 85.
OG Card (1200x630)
Generate Open Graph card with title/subtitle overlay on a background image or solid colour. Apply semi-transparent overlay for text readability. Centre text horizontally.
Common Workflows
Logo Cleanup (client-supplied JPG with white background)
- Trim whitespace
- Convert to PNG (for transparency)
- Create favicon-sized version (thumbnail at 512px)
Prepare Hero Image for Production
Resize to max width 1920, convert to WebP, compress at quality 85.
Batch Process
For multiple images, generate a single script that loops over all files rather than processing one at a time.
Pipeline with Gemini Image Gen
Generate images with the gemini-image-gen skill, then process them:
- Generate with Gemini (raw PNG output)
- User picks favourite
- Optimise: resize to target width, convert to WebP, compress
Output Format Guide
| Use case | Format | Why |
|---|---|---|
| Photos, hero images | WebP | Best compression, wide browser support |
| Logos, icons (need transparency) | PNG | Lossless, supports alpha |
| Fallback for older browsers | JPG | Universal support |
| Thumbnails | WebP or JPG | Small file size priority |
| OG cards | PNG | Social platforms handle PNG best |
Reference Files
| When | Read |
|---|---|
| Implementing any Pillow operation | references/pillow-patterns.md |