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OCR Language Packs and Setup

This document provides instructions on how to add additional language packs for the OCR tab in Stirling-PDF, both inside and outside of Docker.

My OCR used to work and now doesn't!

The paths have changed for the tessdata locations on new Docker images. Please use /usr/share/tessdata (Others should still work for backward compatibility but might not).

How does the OCR Work

Stirling-PDF uses OCRmyPDF, which in turn uses Tesseract for its text recognition. All credit goes to them for this awesome work!

Language Packs

Tesseract OCR supports a variety of languages. You can find additional language packs in the Tesseract GitHub repositories:

  • tessdata_fast: These language packs are smaller and faster to load but may provide lower recognition accuracy.
  • tessdata: These language packs are larger and provide better recognition accuracy, but may take longer to load.

Depending on your requirements, you can choose the appropriate language pack for your use case. By default, Stirling-PDF uses tessdata_fast for English, but this can be replaced.

Installing Language Packs

  1. Download the desired language pack(s) by selecting the .traineddata file(s) for the language(s) you need.
  2. Place the .traineddata files in the Tesseract tessdata directory: /usr/share/tessdata

DO NOT REMOVE EXISTING eng.traineddata, IT'S REQUIRED.

Docker Setup

If you are using Docker, you need to expose the Tesseract tessdata directory as a volume in order to use the additional language packs.

Docker Compose

Modify your docker-compose.yml file to include the following volume configuration:

services:
  your_service_name:
    image: your_docker_image_name
    volumes:
      - /location/of/trainingData:/usr/share/tessdata

Docker Run

Add the following to your existing Docker run command:

-v /location/of/trainingData:/usr/share/tessdata

Non-Docker Setup

If you are not using Docker, you need to install the OCR components, including the ocrmypdf app. You can see the OCRmyPDF install guide.

For Debian-based systems, install languages with this command:

sudo apt update &&\
# All languages
# sudo apt install -y 'tesseract-ocr-*'

# Find languages:
apt search tesseract-ocr-

# View installed languages:
dpkg-query -W tesseract-ocr- | sed 's/tesseract-ocr-//g'

For Fedora:

# All languages
# sudo dnf install -y tesseract-langpack-*

# Find languages:
dnf search -C tesseract-langpack-

# View installed languages:
rpm -qa | grep tesseract-langpack | sed 's/tesseract-langpack-//g'