e6bf3dd290
Implement per-word validation filter for assisted-OCR BrokenVector path. Changes: - Add SpanSource::OcrAssisted variant to hybrid.rs - Add Span::ocr_assisted() helper method - Implement validate_ocr_with_position_hints() in ocr.rs - 5pt distance threshold for position validation - 0.4 confidence cap for rejected words - Linear scan for nearest-neighbor lookup - Add unit tests for validation filter Closes: pdftract-3s2i Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
60 lines
3.1 KiB
Markdown
60 lines
3.1 KiB
Markdown
# pdftract-xzfkt: Caption block classifier - Verification
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## Summary
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Implemented the caption block classifier for Phase 4 layout analysis. The module identifies blocks as captions based on font size, proximity to figures, and column alignment.
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## Implementation
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- **Module**: `crates/pdftract-core/src/layout/caption.rs`
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- **Public API**:
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- `Block` - Block struct with layout properties (kind, text, median_font_size, bbox, column)
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- `PageContext` - Page metrics (page_body_median, line_height, num_columns)
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- `classify_caption(block, prev_block, ctx) -> bool` - Single block classifier
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- `classify_page_captions(blocks, ctx)` - Batch classifier for all blocks on a page
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## Classification Criteria
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A block is classified as a caption when ALL of the following are true:
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1. `block.median_font_size < ctx.page_body_median` (smaller font)
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2. `vertical_distance(block.top, prev_figure.bottom) < 2 * ctx.line_height` (within 2 lines)
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3. `block.column == figure.column` (same column, only checked if num_columns > 1)
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## Test Results
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All 9 unit tests passed:
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- `test_caption_immediately_below_figure` - Caption 1 line below figure → PASS
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- `test_caption_too_far_below_figure` - Caption 3+ lines below → NOT caption
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- `test_caption_font_not_smaller` - Same font size as body → NOT caption
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- `test_caption_different_column` - Two-column layout, different columns → NOT caption
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- `test_no_previous_figure` - No previous block → NOT caption
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- `test_caption_above_figure` - Caption positioned above figure → NOT caption (v0.1.0 limitation)
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- `test_page_classification` - Multi-block page classification → PASS
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- `test_block_accessors` - Block geometry methods → PASS
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## Acceptance Criteria Status
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| Criterion | Status |
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|-----------|--------|
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| Block immediately below Figure, small font, same column → kind: Caption | PASS |
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| Block 5 lines below Figure → NOT Caption | PASS |
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| Block with body-size font below Figure → NOT Caption | PASS |
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| Block in different column from Figure → NOT Caption | PASS |
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| Markdown emission of Caption block (Phase 6.5) | N/A - Future phase |
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## Compilation & Linting
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- `cargo check --all-targets` - PASS
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- `cargo clippy --lib` - PASS (no warnings in layout module)
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- `cargo test --lib caption` - 9/9 tests PASS
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## Files Modified
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- `crates/pdftract-core/src/layout/caption.rs` - New module (277 lines)
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- `crates/pdftract-core/src/layout/mod.rs` - New module file
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- `crates/pdftract-core/src/lib.rs` - Added `pub mod layout;`
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- `clippy.toml` - Fixed invalid configuration option
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## Git Commit
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- Commit: `597f536` (feat(pdftract-xzfkt): implement caption block classifier)
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- Pushed to: `main` branch
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## Notes
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- The classifier works with the assumption that Figure blocks are already detected (sibling bead: figure detection)
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- Caption-above-figure detection is NOT implemented in v0.1.0 per the critical considerations
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- Column membership is assumed to be computed by Phase 4.3 (not yet implemented)
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- Line height is assumed to be computed by Phase 4.2 (not yet implemented)
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- The implementation is self-contained and ready for integration once the Phase 4 pipeline is complete
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