diff --git a/notes/pdftract-2b7ff.md b/notes/pdftract-2b7ff.md new file mode 100644 index 0000000..cee8a3a --- /dev/null +++ b/notes/pdftract-2b7ff.md @@ -0,0 +1,56 @@ +# Verification Note: pdftract-2b7ff + +## Bead: image_coverage_fraction signal evaluator + +## Status: PASS ✅ + +The `image_coverage_fraction` signal evaluator was already implemented in the codebase at `/home/coding/pdftract/crates/pdftract-core/src/classify.rs` (lines 359-413). + +## Implementation Details + +### Signature +```rust +pub fn image_coverage_fraction(ctx: &PageContext) -> Option +``` + +### Algorithm +1. Compute page area: `page_area_pt2 = ctx.width * ctx.height` +2. Guard against zero/negative page area (returns `None`) +3. Sum all `image_xobject_areas` to get total image coverage +4. Compute coverage fraction: `total_image_area / page_area_pt2` +5. Clamp to `[0.0, 1.0]` to handle overlapping images defensively +6. If `coverage_fraction > 0.85`: return `Some(Vote::scanned(0.85))` + +### Trade-offs Documented in Code +The implementation uses `sum` instead of `union` for simplicity, with a clear comment noting: +- 5 overlapping copies of one image = sum of 5x area but union is 1x area +- This is acceptable for the 0.85 threshold (conservative signal) +- Revisit with Klee's algorithm (~O(N log N)) if accuracy demands + +## Acceptance Criteria Verification + +| AC | Status | Notes | +|---|--------|-------| +| Page with one image covering 90% area → Some(Vote { 0.85, Scanned }) | ✅ PASS | Lines 2698-2713 test this exact case | +| Page with multiple small images totaling 50% → None | ✅ PASS | Lines 2715-2730 test this exact case | +| Page with no images → None | ✅ PASS | Lines 2732-2743 test this exact case | +| Coverage clamped to 1.0 on overlapping images | ✅ PASS | Lines 2745-2766 test 5x overlapping images | + +## Additional Tests Verified + +| Test Case | Status | +|-----------|--------| +| Exactly 85% threshold (just above) | ✅ PASS (lines 2769-2783) | +| Just below 85% threshold | ✅ PASS (lines 2785-2797) | +| Zero page area | ✅ PASS (lines 2799-2810) | +| Negative page area | ✅ PASS (lines 2812-2823) | +| Multiple images totaling 90% | ✅ PASS (lines 2839-2856) | + +## Conclusion + +The implementation is complete, correct, and thoroughly tested. All acceptance criteria pass. The bead is ready to close. + +## Files Reviewed + +- `/home/coding/pdftract/crates/pdftract-core/src/classify.rs` - Main implementation (lines 359-413) +- `/home/coding/pdftract/crates/pdftract-core/src/classify.rs` - Tests (lines 2696-2889)