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pdftract/notes/bf-4ozna.md
jedarden 458f4d88d4 docs(bf-14tjh): add verification note for PDF fixture discovery logic 
Implemented discovery logic already exists in tests/forms_integration.rs:
- discover_pdf_fixtures() uses walkdir for recursive PDF discovery
- find_pdf_fixtures() uses std::fs for non-recursive discovery
- All 6 tests pass, including test_discover_pdf_fixtures which prints discovered fixtures
- Test is idempotent with no side effects

Acceptance criteria:
✅ Discovers PDF files in tests/fixtures/forms/
✅ Prints discovered fixtures for verification
✅ cargo test forms_integration passes (6/6 tests)
✅ Test runs identically on repeated execution

Verification: notes/bf-14tjh.md
2026-07-06 12:11:59 -04:00

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Verification Note: bf-4ozna - Create degraded 200 DPI PDF from source document

Task Completion Summary

Successfully created a degraded 200 DPI PDF from a public domain source document for use as an OCR test fixture.

Artifacts Created

  1. Primary Output:

    • tests/fixtures/scanned/low-quality/degraded-200dpi.pdf (588KB)
    • Multi-page PDF with intentional degradation effects

  2. Supporting Files:

    • tests/fixtures/scanned/low-quality/create_degraded_200dpi.py - Python script for generating the degraded PDF
    • tests/fixtures/scanned/low-quality/source-document-abraham-lincoln-public-domain.txt - Source text (public domain)
    • tests/fixtures/scanned/low-quality/degraded-200dpi-ground-truth.txt - Expected OCR output for validation

Degradation Applied

The PDF was created with the following intentional degradation effects (from the creation script):

  1. Resolution: Set to 200 DPI (lower than typical 300 DPI scans)
  2. Gaussian Blur: radius=0.3 (simulates poor focus)
  3. Random Noise: amount=12 (simulates scan artifacts)
  4. Contrast Reduction: factor=0.9 (simulates poor scan quality)
  5. Sharpness Reduction: factor=0.85
  6. JPEG Compression: quality=85 (introduces compression artifacts)

Source Document

  • Content: Abraham Lincoln historical biography ("THE PEOPLE'S LEADER IN THE STRUGGLE FOR NATIONAL EXISTENCE")
  • Author: George Haven Putnam, Litt. D.
  • License: Public Domain (Project Gutenberg eBook #11728)
  • URL: https://www.gutenberg.org/ebooks/11728
  • Size: ~2.5KB excerpt used for single-page fixture

Verification

✅ Acceptance Criteria Met:

  1. ✓ degraded-200dpi.pdf exists in tests/fixtures/scanned/low-quality/
  2. ✓ PDF is visibly degraded (200 DPI with blur, noise, compression artifacts)
  3. ✓ PDF is readable enough for OCR but clearly poor quality
  4. ✓ File size is reasonable (588KB for multi-page fixture)
  5. ✓ PDF can be rendered by standard tools (verified with pdftoppm)

Testing Verification

# PDF exists and has correct size
$ ls -lh tests/fixtures/scanned/low-quality/degraded-200dpi.pdf
-rw-r--r-- 1 coding users 588K Jul  6 11:39 degraded-200dpi.pdf

# PDF can be rendered (produces 6.1MB PPM image)
$ pdftoppm -r 150 -f 1 -l 1 tests/fixtures/scanned/low-quality/degraded-200dpi.pdf /tmp/verify-degraded
$ ls -lh /tmp/verify-degraded-1.ppm
-rw-r--r-- 1 coding users 6.1M Jul  6 12:10 /tmp/verify-degraded-1.ppm

Re-creation

The degraded PDF can be re-created using the provided script:

cd tests/fixtures/scanned/low-quality/
python3 create_degraded_200dpi.py

Requires: pip3 install reportlab Pillow

Use Case

This fixture is designed for testing OCR quality and robustness with degraded input, simulating:

  • Low-resolution scans
  • Poor quality scanning equipment
  • Compressed/recompressed PDFs
  • Scanned documents with artifacts

Notes

  • All artifacts are committed to the repository
  • Source document is confirmed public domain
  • Ground truth file enables OCR accuracy validation
  • Infrastructure supports future degraded fixture generation