Brent Perteet
2719ec244d
Created split_png_by_brightness.py to split rasterized logos into separate SVG files by color for Underground Magnetics logo conversion. Key features: - OpenCV contour hierarchy detection for proper hole handling - Letters with enclosed shapes (d, o, g, etc.) now render correctly - Tight brightness thresholds to avoid antialiasing artifacts - Automatic bounding box cropping for optimal file sizes - Black text: brightness < 40 (236k pixels, 21 shape groups) - Grey icon: brightness 108-118 (119k pixels, 2 shape groups) Results: - um_black.svg: 6.1KB, 3070x233px (was 139KB, 3613x391px) - um_grey.svg: 728B, 413x390px (was 253KB, 3613x391px) Files: - split_png_by_brightness.py: Main color separation tool - IMPROVEMENTS.md: Detailed changelog and comparison - README_underground_magnetics.md: Usage documentation - underground-magnetics.eps: Source logo file - um_black.svg: Separated black text (cropped) - um_grey.svg: Separated grey icon (cropped) - requirements.txt: Added opencv-python dependency 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
2.0 KiB
2.0 KiB
Improvements to split_png_by_brightness.py
Version 2 Fixes
1. Proper Hole Handling
Problem: Letters with enclosed shapes (like "d", "o", "g") were missing their holes, making them appear filled.
Solution:
- Switched from
scikit-imagecontour detection to OpenCV'scv2.findContourswithRETR_CCOMPmode - This detects contour hierarchy (parent/child relationships)
- Holes are now included in the same SVG path as their parent contour
- Using
fill-rule="evenodd"properly renders the holes
2. Better Color Detection
Problem: Antialiasing pixels around edges were being included, creating artifacts and incorrect bounding boxes.
Solution:
- Changed from single threshold to tight ranges
- Black text: brightness < 40 (was < 50)
- Grey icon: brightness 108-118 (was 80-120)
- This excludes antialiased edge pixels and prevents the grey icon from spanning the full image width
3. Automatic Bounding Box Cropping
Problem: SVG files contained a lot of empty space.
Solution:
- Added automatic cropping to bounding box by default
- Each SVG is sized to fit its content exactly
--no-cropflag available if full canvas is needed
Results
Before (v1):
- um_black.svg: 139K, 27 separate paths, many filled letters
- um_grey.svg: 253K, 1609 paths, antialiasing artifacts, full width (3613px)
After (v2):
- um_black.svg: 6.1K, 21 shape groups with proper holes, cropped to 3070x233
- um_grey.svg: 728B, 2 shape groups, clean edges, cropped to 413x390
Dependencies Added
- opencv-python==4.13.0.92
Default Parameters
- Black threshold: < 40 brightness
- Grey range: 108-118 brightness
- Cropping: enabled by default
Usage
# Default (optimized for Underground Magnetics logo)
python split_png_by_brightness.py input.png --prefix output
# Custom thresholds
python split_png_by_brightness.py input.png \
--dark-threshold 40 \
--mid-min 108 \
--mid-max 118
# Disable cropping
python split_png_by_brightness.py input.png --no-crop