PDFRedlines

Fast PDF redline extraction via a Rust NIF (MuPDF).

Usage

{:ok, result} = PDFRedlines.extract_redlines("/path/to/document.pdf")
# %PDFRedlines.Result{redlines: [%PDFRedlines.Redline{...}, ...]}

What Are Redlines?

Redlines are tracked changes embedded in PDFs, typically represented as:

• Deletions: colored text with a strikethrough line through the middle.
• Insertions: colored text with an underline below the text.

This library detects those visual signals and converts them into structured entries (deletion, insertion, or paired change).

Notes

• This library is intentionally small and focused on the minimal API we need.
• Precompiled NIFs are published in GitHub Releases; set PDF_REDLINES_BUILD=1 to force a local build.

Configuration

You can pass a keyword list or map to tune detection thresholds:

• :red_r_min
• :red_g_max
• :red_b_max
• :blue_r_max
• :blue_g_max
• :blue_b_min
• :formatting_bar_height_max
• :formatting_bar_width_min
• :line_bar_height_max
• :line_bar_width_min
• :stroke_line_y_tolerance
• :stroke_line_width_min
• :line_break_height_ratio
• :same_line_y_tolerance
• :merge_x_gap_max
• :merge_line_height_min_ratio
• :merge_line_height_max_ratio
• :margin_end_ratio
• :margin_start_ratio
• :pair_x_gap_max
• :page_width_fallback
• :line_height_fallback

Tuning Guide (Quick)

• If strikethroughs are missed, try increasing:
  • :formatting_bar_height_max
  • :stroke_line_width_min (if lines are thicker)
• If underlines are missed, try increasing:
  • :line_bar_height_max
  • :line_bar_width_min
• If colors are missed, widen:
  • :red_r_min (lower for lighter reds)
  • :blue_b_min (lower for lighter blues)
• If line wrapping isn’t merged, adjust:
  • :merge_line_height_min_ratio, :merge_line_height_max_ratio
  • :margin_start_ratio, :margin_end_ratio

Parity Test (Optional)

There is an optional parity test that compares Rust/MuPDF results against the Python/PyMuPDF implementation. It is skipped by default.

Run it with:

TEST_PDF_REDLINES_PARITY=true mix test test/redlines_parity_test.exs

Inputs are read from PDF_REDLINES_TEST_DIR (defaults to test/fixtures/pdfs).

Performance

Extraction runs entirely in a Rust NIF on a dirty scheduler. Benchmarked on real-world documents (M1 Mac):

Even the worst case (large scanned documents) finishes under 700 ms.

Benchmarks

Run a basic benchmark across a folder of PDFs:

PDF_REDLINES_BUILD=1 mix pdf_redlines.bench

You can customize:

• PDF_REDLINES_TEST_DIR (default test/fixtures/pdfs)
• PDF_REDLINES_BENCH_REPEATS (default 3)

Development

To compile the Rust sources along with the library, you can set the RUSTLER_PRECOMPILED_FORCE_BUILD_ALL env variable to 1, e.g.:

RUSTLER_PRECOMPILED_FORCE_BUILD_ALL=1 mix compile

License

MIT