70 lines
2.4 KiB
Markdown
70 lines
2.4 KiB
Markdown
# Algorithm Overview {#algorithm-overview}
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This page provides a high-level overview of how Quagga2 processes images to detect and decode barcodes.
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## Processing Pipeline {#processing-pipeline}
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Quagga2 processes each frame through a multi-stage pipeline:
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```
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Input Image → Preprocessing → Localization → Decoding → Result
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```
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### 1. Preprocessing {#preprocessing}
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- **Scaling**: Image is resized based on `inputStream.size`
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- **Grayscale conversion**: Color image converted to grayscale
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- **Area cropping**: If `inputStream.area` is set, crop to that region
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### 2. Localization {#localization}
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When `locate: true` (default):
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1. **Binarization**: Convert to black/white using Otsu's method
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2. **Grid division**: Split image into patches
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3. **Skeletonization**: Extract line structures
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4. **Pattern analysis**: Find barcode-like patterns
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5. **Bounding box**: Calculate barcode region
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See [How Barcode Localization Works](how-barcode-localization-works.md) for detailed explanation.
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### 3. Decoding {#decoding}
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1. **Scanline extraction**: Sample pixels along detected barcode
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2. **Pattern matching**: Match bar/space patterns to barcode format
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3. **Character decoding**: Convert patterns to characters
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4. **Checksum validation**: Verify barcode integrity
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## Key Algorithms {#key-algorithms}
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### Otsu's Method {#otsus-method}
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Automatic threshold selection for binarization. Adapts to varying lighting conditions by analyzing the image histogram.
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### Connected Component Labeling {#connected-component-labeling}
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Groups adjacent pixels into distinct regions. Used during localization to identify potential barcode patterns.
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### Image Moments {#image-moments}
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Mathematical technique to calculate orientation and position of detected patterns.
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## Performance Characteristics {#performance-characteristics}
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| Factor | Impact | Mitigation |
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|--------|--------|------------|
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| Image size | Linear increase | Use `inputStream.size` |
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| Number of readers | Linear increase | Only enable needed readers |
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| Localization | ~60% of processing time | Use `locate: false` if position known |
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| Half sampling | 4x faster | Keep `halfSample: true` |
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## Related {#related}
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- [How Barcode Localization Works](how-barcode-localization-works.md) - Detailed localization explanation
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- [Architecture](architecture.md) - Code structure overview
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- [Optimize Performance](../how-to-guides/optimize-performance.md) - Performance tuning
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---
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[← Back to Explanation](index.md)
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