🔍 LiveTrans: Privacy-First Real-Time Screen Translation Engine

A sophisticated, local-first desktop translation tool for Linux that provides real-time, context-aware translation of on-screen text. Built with PyQt6, Tesseract OCR, and LibreTranslate, LiveTrans brings professional AR-style translation capabilities to your desktop—entirely offline and privacy-respecting.

No cloud. No data leaks. Just pure local translation.

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✨ Features

Core Capabilities

• Real-Time Translation: Seamlessly translate text visible on your screen with sub-100ms latency
• Context-Aware: Groups spatially-related words before translation to preserve meaning (critical for languages like Japanese)
• Multi-Language Support: English, French, German, Spanish, Japanese, and more
• Privacy-First: All processing happens locally—your screen data never leaves your machine
• Universal Compatibility: Works on any Linux window (VS Code, browsers, PDF readers, terminals, etc.)

Technical Highlights

• Hierarchical Layout Analysis: YOLO-like spatial mapping clusters words into semantic blocks
• Recursive Feedback Prevention: Intelligent "blink-and-capture" prevents the overlay from translating itself
• Optimized Image Processing: Grayscale conversion and 2x upscaling for pixel-perfect OCR accuracy
• Multi-Threaded Pipeline: Separate UI and worker threads keep your interface buttery-smooth
• Smart Caching: Translations are cached to minimize redundant processing and CPU usage
• Coordinate Remapping: Translatable text boxes land exactly where the original text appears

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🚀 Installation

System Dependencies

First, update your package manager and install the required system libraries:

sudo apt-get update
sudo apt-get install -y python3-venv python3-dev build-essential cmake tesseract-ocr libtesseract-dev tesseract-ocr-eng tesseract-ocr-fra tesseract-ocr-deu tesseract-ocr-spa tesseract-ocr-jpn

LibreTranslate Setup (Required)

LiveTrans requires LibreTranslate running as a background service. Start it in a separate terminal before launching the application.

Quick Start (Japanese & English only):

libretranslate --load-only ja,en --port 5000

This will download the required language models on first run.

Recommended (Multi-Language Support): For broader language support, use:

libretranslate --load-only ja,en,zh,ko,fr,es --port 5000

This loads models for: Japanese, English, Chinese, Korean, French, and Spanish.

Note: The first run will download language models (may take a few minutes depending on your internet speed). Subsequent runs will start quickly.

Python Environment Setup

1. Clone or navigate to the project directory:

   cd /path/to/Linux-Translator

2. Create a Python virtual environment:

   python3 -m venv venv

3. Activate the virtual environment:

   source venv/bin/activate

4. Install Python dependencies:

   pip install -r requirements.txt

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📖 Quick Start

Prerequisites

Ensure LibreTranslate is running in a separate terminal before launching the application:

# Terminal 1: Start LibreTranslate (runs indefinitely)
libretranslate --load-only ja,en,zh,ko,fr,es --port 5000

Running the Application

Once LibreTranslate is active and the virtual environment is activated, start LiveTrans in another terminal:

# Terminal 2: Start LiveTrans
source venv/bin/activate
python src/main.py

A translucent overlay window will appear on your screen, ready to capture and translate on-screen text.

Basic Usage

1. Ensure LibreTranslate is Running:

   • Keep it running in a separate terminal (it will run until you stop it)
   • You should see output like "WARNING: Running in debug mode. This is not recommended for production."

2. Launch the Application:

   source venv/bin/activate
   python src/main.py

3. Position the Overlay:

   • Click and drag to move the translation window
   • Click and drag the edges to resize it to the area you want to monitor

4. Select Source & Target Languages:

   • Use the dropdown menus to choose your source language (e.g., Japanese)
   • Choose your target language (e.g., English)

5. Watch the Magic:

   • The application continuously captures your selected area
   • Text is detected via OCR (Tesseract)
   • Translations appear in real-time within the overlay
   • Hover over translations to see original text (if applicable)

6. Stop the Application:

   • Close the overlay window or press Ctrl+C in the terminal
   • Keep LibreTranslate running in its terminal for future use (or stop it with Ctrl+C when done)

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🏗️ Architecture Overview

Multi-Threaded Pipeline

┌─────────────────────────────────────┐
│     Main Thread (UI / PyQt6)        │
│  • Manages ViewportWindow           │
│  • Receives mouse drag/resize input │
│  • Draws translated overlay         │
│  • Emits frame_captured signal      │
└────────────────┬────────────────────┘
                 │ (signals)
                 ▼
┌─────────────────────────────────────┐
│   Worker Thread (OCR/Translation)   │
│  • Awaits frame_captured signal     │
│  • Performs Tesseract OCR           │
│  • Groups words by spatial layout   │
│  • Calls LibreTranslate             │
│  • Emits finished signal            │
└─────────────────────────────────────┘

Key Components

1. The Viewport (viewport.py)

• PyQt6 window displaying the translation overlay
• Handles mouse interactions for window movement/resizing
• Triggers the "blink" mechanism to prevent feedback loops

2. OCR Engine (ocr.py)

• Leverages Tesseract's image_to_data() for word-level detection
• Performs hierarchical layout analysis by grouping words via block/paragraph/line IDs
• Applies pre-processing: grayscale conversion and 2x cubic upscaling
• Remaps coordinates from upscaled image back to original dimension

3. Translation Engine (translator.py)

• Manages LibreTranslate API calls
• Caches translations to avoid redundant processing
• Joins words contextually (no spaces for CJK languages, spaces for others)

4. Main Pipeline (main.py)

• Orchestrates the multi-threaded workflow
• Manages signal/slot connections between UI and Worker threads
• Implements the "blink-and-capture" mechanism

The "Blink-and-Capture" Mechanism

To prevent the overlay from translating itself (recursive feedback):

1. UI sets hide_temp = True → overlay becomes invisible
2. UI repaints the screen (now clean, showing only source text)
3. mss takes a screenshot of the pure original text
4. UI sets hide_temp = False → overlay reappears
5. All this happens in ~50 milliseconds—imperceptible to humans but clean for the OCR engine

Spatial Word Grouping (Hierarchical Layout Analysis)

Instead of treating text as individual words, we group them by:

• block_num: Major content blocks
• par_num: Paragraphs within blocks
• line_num: Lines within paragraphs

This ensures that Japanese text "日本語" is translated as a single semantic unit, not three separate characters with different meanings.

Image Optimization Pipeline

Original Screen Capture
         ▼
[Grayscale Conversion] → Remove color noise
         ▼
[2x Cubic Upscaling]   → Sharpen character edges
         ▼
[Tesseract OCR]        → Detect words + coordinates
         ▼
[Coordinate Remap]     → Convert back to original scale (÷ 2)
         ▼
[Layout Analysis]      → Group by block/paragraph/line
         ▼
[LibreTranslate]       → Translate grouped words
         ▼
[Cache & Display]      → Show translation in overlay

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⚙️ Configuration

Supported Languages

OCR Languages (via Tesseract):

• English (eng)
• French (fra)
• German (deu)
• Spanish (spa)
• Japanese (jpn)
• Additional languages can be installed

Translation Languages (via LibreTranslate):

• English, French, German, Spanish, Japanese, Chinese, Korean, Russian, Portuguese, Italian, Dutch, Polish, Turkish, and more

Adjustable Parameters

Edit the source files to customize:

• Overlay opacity and colors in viewport.py
• OCR processing parameters (upscale factor, grayscale) in ocr.py
• Translation cache size and source mapping in translator.py
• Capture interval and thread priorities in main.py

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🔒 Privacy & Security

• ✅ Zero Cloud Dependency: All processing is local
• ✅ No Data Transmission: Your screen data never leaves your machine
• ✅ Self-Hosted Translation Engine: LibreTranslate runs locally on localhost:5000
• ✅ Open Source: Inspect the code yourself
• ✅ Offline-Capable: After models are downloaded, works entirely offline

Data Flow: Screenshots → Tesseract OCR (local) → LibreTranslate (local) → UI Display. No external API calls.

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📊 Performance Characteristics

Metric	Value
Frame Capture Latency	~20-50ms
OCR Processing	~50-150ms (depends on text density)
Translation Round-Trip	~100-300ms (cached: <1ms)
UI Responsiveness	Real-time (separate thread)
Memory Footprint	~150-300 MB (varies by overlay size)
CPU Usage	Minimal when idle; scales with text density

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🛠️ Troubleshooting

LibreTranslate not running

libretranslate --load-only ja,en,zh,ko,fr,es --port 5000

Ensure this command is running in a separate terminal. If the port is already in use:

libretranslate --load-only ja,en,zh,ko,fr,es --port 5001

(Then update the port in translator.py accordingly)

"Tesseract not found" error

Ensure you installed the system dependencies:

sudo apt-get install tesseract-ocr libtesseract-dev

Low OCR accuracy

• Increase the upscale factor in ocr.py (default is 2x)
• Ensure the captured area has good contrast
• Try adjusting the grayscale threshold

Overlay not appearing

• Check that PyQt6 is installed: pip install PyQt6
• Verify your display server supports the windowing system

Translation not working

• Verify LibreTranslate is running: curl http://localhost:5000/ (should show HTML response)
• Check that the port matches your configuration
• Review logs in the console for error messages
• Ensure required language models are loaded

Performance lag

• Reduce the size of the monitored area
• Disable features temporarily to isolate the bottleneck
• Check system RAM availability
• Ensure LibreTranslate isn't overloaded with requests

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📚 Development & Future Improvements

Roadmap (Version 2.0)

• Vertical Text Support: Toggle for vertical OCR (ideal for manga/traditional Japanese literature)
• Smart Inpainting: Replace black boxes with OpenCV inpaint/blur using surrounding colors
• Alpha-Blended Boxes: Transparent or rounded-corner styling for modern aesthetics
• Custom Styling: User-configurable fonts, colors, and background effects
• Multi-Window Support: Translate multiple windows simultaneously
• Hotkey Bindings: Keyboard shortcuts for language switching and pause/resume

Contributing

To extend LiveTrans:

1. Set up your development environment (see Installation)
2. Review the architecture in Architecture Overview
3. Make your changes in the appropriate module (ocr.py, translator.py, viewport.py, etc.)
4. Test with the provided test suite: python -m pytest tests/
5. Submit improvements or bug reports!

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📄 License

See LICENSE for details.

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🙏 Acknowledgments

• Tesseract OCR: Open-source optical character recognition engine
• LibreTranslate: Free, open-source machine translation API
• mss: Lightweight screen capture library
• PyQt6: Cross-platform GUI toolkit

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💬 Support

Encountered an issue? Here's how to debug:

1. Enable verbose logging:

   python src/main.py --verbose

2. Check dependency versions:

   pip list
   tesseract --version

3. Inspect the logs: Check console output for detailed error messages

4. Review test cases: See tests/ for examples of OCR and translation workflows

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Happy translating! 🌍