182 lines
5.0 KiB
Markdown
182 lines
5.0 KiB
Markdown
# PDF Layer Extractor for Industrial Diagrams
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Extract colored layers from PDF industrial diagrams with white backgrounds. Automatically handles variable layer counts and antialiasing around text.
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## Features
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- **PDF Support**: Direct PDF processing at configurable DPI
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- **Automatic Layer Detection**: K-means clustering identifies distinct colored layers
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- **Handles Antialiasing**: Tolerates color mixing around text and fine details
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- **Variable Layer Counts**: Auto-detects all colored layers
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- **Strict White Filtering**: Pure white (255,255,255) treated as background only
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- **High Quality Output**: Each layer saved as transparent PNG
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## Installation
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```bash
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pip install -r requirements.txt
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```
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## Quick Start
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```bash
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# Basic usage
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python layer_extractor.py diagram.pdf
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# Higher resolution
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python layer_extractor.py diagram.pdf --dpi 600
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# Extract to specific folder
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python layer_extractor.py diagram.pdf -o my_layers/
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```
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## Usage
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### Basic Command
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```bash
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python layer_extractor.py diagram.pdf
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```
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Output: `output/diagram_layer1_255_000_000.png`, `output/diagram_layer2_000_000_255.png`, etc.
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### Common Options
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```bash
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# High resolution rendering (better for detailed diagrams)
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python layer_extractor.py diagram.pdf --dpi 600
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# Adjust color tolerance (for antialiasing issues)
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python layer_extractor.py diagram.pdf -t 40
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# Extract only top 3 layers
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python layer_extractor.py diagram.pdf -n 3
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# Custom output directory
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python layer_extractor.py diagram.pdf -o layers/
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```
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## Parameters
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- `--dpi` (default: 300) - PDF rendering resolution
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- 300: Standard quality, faster
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- 600: High quality, larger files
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- 150: Draft quality, quick preview
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- `-t, --tolerance` (default: 30) - Color matching tolerance (0-100 scale)
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- **10-15**: Very strict, only nearly identical colors
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- **20-25**: Strict, minimal antialiasing
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- **30**: Default, handles moderate antialiasing (RECOMMENDED)
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- **40-50**: Lenient, good for heavy antialiasing around text
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- **60+**: Very lenient, may blur layer boundaries
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- `-n, --n-layers` - Extract specific number of layers (default: auto-detect)
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- `-m, --min-pixels` (default: 100) - Minimum pixels to consider a valid layer
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## How It Works
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1. **PDF Rendering**: Converts PDF to high-resolution image at specified DPI
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2. **Color Analysis**: Uses K-means clustering on pixel colors
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3. **White Filtering**: Removes pure white background (RGB ≥ 250,250,250)
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4. **Layer Extraction**: For each color, creates a mask of similar pixels
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5. **Alpha Blending**: Handles antialiasing with gradient transparency
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6. **Output**: Saves each layer as transparent PNG
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## Output Format
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Files are named: `{pdf_name}_layer{N}_{R}_{G}_{B}.png`
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Example:
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```
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output/
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├── piping_diagram_layer1_220_050_050.png (Red layer)
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├── piping_diagram_layer2_050_100_220.png (Blue layer)
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└── piping_diagram_layer3_050_180_050.png (Green layer)
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```
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## Troubleshooting
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### Colors bleeding between layers (antialiasing issue)
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**Problem**: Gray pixels from antialiasing appearing in wrong layer, especially around black text on gray layers
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**Explanation**: When black text (0,0,0) sits on a gray layer (150,150,150), antialiasing creates intermediate grays (75,75,75, 100,100,100, etc.) that are far from both black and gray in color space.
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**Solution**: Increase tolerance to capture these intermediate colors
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```bash
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# For moderate antialiasing (default, usually works)
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python layer_extractor.py diagram.pdf -t 30
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# For heavy antialiasing (small text, compressed PDFs)
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python layer_extractor.py diagram.pdf -t 45
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# For extreme cases (very compressed or low quality)
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python layer_extractor.py diagram.pdf -t 60
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```
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### Missing fine details
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**Problem**: Thin lines or small text not captured
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**Solution**: Increase tolerance or DPI
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```bash
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python layer_extractor.py diagram.pdf -t 40 --dpi 600
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```
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### Too many layers detected
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**Problem**: Small color artifacts creating extra layers
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**Solution**: Increase minimum pixel threshold
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```bash
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python layer_extractor.py diagram.pdf -m 500
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```
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### Blurry output
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**Problem**: Output quality not good enough
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**Solution**: Increase DPI
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```bash
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python layer_extractor.py diagram.pdf --dpi 600
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```
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## Examples
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### Standard industrial diagram
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```bash
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python layer_extractor.py electrical_schematic.pdf
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```
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### High-detail mechanical drawing
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```bash
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python layer_extractor.py mechanical_drawing.pdf --dpi 600 -t 25
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```
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### Diagram with known 4 layers
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```bash
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python layer_extractor.py hvac_diagram.pdf -n 4
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```
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### Compressed/low-quality PDF
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```bash
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python layer_extractor.py scanned_diagram.pdf -t 50 --dpi 300
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```
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## Tips
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1. **Start with defaults** - They work for most diagrams
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2. **Check first** - Run once and review output before batch processing
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3. **DPI vs File Size** - Higher DPI = better quality but larger files
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4. **Tolerance tuning** - Adjust by ±5-10 at a time
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5. **Layer count** - Use `-n` if you know exact number for faster processing
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## Requirements
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- Python 3.7+
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- PyMuPDF (PDF rendering)
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- Pillow (image processing)
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- NumPy (array operations)
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- scikit-learn (color clustering)
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