Lege - 1.4.1

Releases are updated with every new version --> https://github.com/LegeApp/Lege/releases/

Turn scanned PDFs (or page-image folders) into clean, compact files that read great on e-ink.

Lege is a document-processing app (CLI + desktop GUI) that converts scanned documents into reader-optimized PDF or DjVu, focusing on better readability, smaller output size, and fast page turns on e-ink devices. It uses layout-aware processing to treat text-like areas differently from image-like areas, so you can keep diagrams/photos while compressing text aggressively.

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What you can do with it

• Convert scanned PDFs → optimized PDF

  • Mixed-content output (compressed text base + image overlays where needed).

• Convert scanned PDFs → DjVu

  • Very strong compression for compatible readers (especially e-ink + KOReader).

• Optional searchable text (OCR)

  • Linux/macOS: Tesseract backend
  • Windows: WinRT OCR backend

• Smart page cleanup

  • Margin workflows (none / standardize-and-center / crop-and-resize)
  • Optional deskew / orientation correction
  • Device/target-size presets for common e-ink screens

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Interfaces

• CLI: guided interactive mode (no args) + direct command modes
• GUI: Dioxus desktop app using the same processing core; queue-based workflow with progress + cancel

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Quick start

Build (from source)

git clone https://github.com/LegeApp/Lege.git
cd Lege
cargo build --release

You’ll get:

• CLI: target/release/lege
• GUI (Dioxus): target/release/lege-gui (name may vary by workspace config)

Run

# simplest: optimized PDF output
lege input.pdf

# DjVu output (optionally with OCR)
lege input.pdf --output-format djvu --ocr

# process a page range
lege input.pdf --pages 10-50

the CLI also supports an interactive guided mode when run without arguments.

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Inputs and outputs

Inputs

• PDF files (with optional page range selection)
• Image-folder mode for sequential page images (used for batch/page-image workflows)
• Debug modes for exporting rendered pages / crops (useful for model and pipeline inspection)

Outputs

• PDF: mixed region encoding (compressed bi-level text + preserved image regions as overlays)
• DjVu: native Rust encoder with JB2 (bi-level) + IW44 (continuous-tone) layering

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External Dependencies

Lege requires several external files to be placed alongside the executables:

Required for all platforms:

ONNX Models (AI inference):

• yolo-layout.onnx - Layout detection (Linux production model)
• paddle-layout.onnx - Layout detection (legacy/non-Linux fallback)
• paddle-rotate.onnx - Page orientation detection
• paddle-deskew.onnx - Page deskew correction
• sauvola.onnx - Adaptive binarization

Platform-specific GPU libraries:

Windows:

• DirectML.dll - DirectML acceleration provider
• onnxruntime.dll - ONNX Runtime main library
• onnxruntime_providers_shared.dll - Shared provider library
• pdfium.dll - PDF rendering engine

Linux:

• libonnxruntime.so - ONNX Runtime
• libonnxruntime_providers_shared.so - Provider library
• libwebgpu_dawn.so - WebGPU/Vulkan backend
• libpdfium.so - PDF rendering engine
• eng.traineddata - Tesseract English language data (for OCR)

macOS:

• libonnxruntime.dylib - ONNX Runtime
• libpdfium.dylib - PDF rendering engine
• Tesseract language data (system installation)

Technical details

High-level pipeline

Lege is an end-to-end document transformation system with distinct pipelines for PDF and DjVu output.

Core stages

1. Render pages (PDF → images) using PDFium (with thread-safety guardrails).

2. Layout inference (optional): run an ONNX layout model on a low-res render; map detections into text-like vs image-like buckets.

3. Region processing

   • Text regions: binarize + encode with bi-level codecs
   • Image regions: preserve/encode separately; composite as overlays where applicable
   • Optional OCR integration at region or page level

4. Assemble output

   • PDF writer actor: ordered page finalize into a single PDF
   • DjVu writer actor: out-of-order page submission + multipage finalize

PDF pipeline vs DjVu pipeline

PDF pipeline (src/pipeline/pdf_tokio_pipeline.rs)

Implemented as a multi-stage async pipeline with bounded channels and configurable concurrency:

• render → inference → CPU page processing → ordered writer/finalizer
• supports page ranges and optional two-pass margin normalization

DjVu pipeline (src/pipeline/djvu_pipeline.rs)

Separate pipeline to match DjVu constraints:

• similar render/inference conceptually
• produces DjVu page payloads submitted to a DjVu writer actor
• supports layered JB2/IW44 output, and optional hidden text

Layout detection

Lege can run layout detection to segment a page into regions and apply different encoding strategies. The exact classes depend on the model used (the existing README references a PaddleX-style detector).

When layout detection is disabled, Lege follows a more uniform “whole-page” processing strategy.

Binarization and image treatment

• Text-like regions are typically converted to 1-bit (bi-level) using adaptive binarization logic in the encoding layer.
• Image-like regions can be preserved/encoded separately and overlaid onto the output (so photos/diagrams don’t get crushed into 1-bit).

Dithering can be used for halftone/image handling depending on the chosen mode and encoder strategy.

OCR and text layers

OCR is optional:

• Linux/macOS: Tesseract
• Windows: WinRT OCR

Strategy:

• prefer bounded region OCR when layout segmentation is workable
• fall back to tiled or full-page OCR as needed
• when OCR is disabled, Lege can optionally reuse/extract text from PDFs that already have a text layer to synthesize a text overlay where possible

Encoding formats and where they’re used

Lege uses a dedicated encoding crate (Legencode) for in-memory processing and multiple output encoders, and a dedicated native DjVu encoder (DJVULibRust) for DjVu generation.

Bi-level / “text compression” codecs

• JBIG2 (via a Rust port under Legencode)
• CCITT Group 4 (fax-style bi-level compression)

Continuous-tone codecs

• JPEG (used for cover/photo regions in common paths)
• DjVu IW44 (continuous-tone layer inside DjVu)

Performance and operability features

• Concurrent pipeline with bounded channels/backpressure
• Cancellation + progress tracking shared by CLI and GUI
• Runtime dependency discovery (models/libs) via executable-adjacent paths, env vars, and platform fallback dirs

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Workspace layout

Lege is a Rust workspace with multiple crates:

• src/ — main app + pipeline orchestration (CLI core)
• Legencode/ — encoding + binarization + region utilities
• DJVULibRust/ — native DjVu encoder crate
• GUI/Dioxus/ — desktop GUI frontend

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Related Projects

License

GPL-3.0. See LICENSE. Third-party licenses are documented under docs/.

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