OCRmyPDF/docs/batch.md

% SPDX-FileCopyrightText: 2022 James R. Barlow % SPDX-License-Identifier: CC-BY-SA-4.0

Batch processing

This article provides information about running OCRmyPDF on multiple files or configuring it as a service triggered by file system events.

Batch jobs

Consider using the excellent GNU Parallel to apply OCRmyPDF to multiple files at once.

Both parallel and ocrmypdf will try to use all available processors. To maximize parallelism without overloading your system with processes, consider using parallel -j 2 to limit parallel to running two jobs at once.

This command will run ocrmypdf on all files named *.pdf in the current directory and write them to the previously created output/ folder. It will not search subdirectories.

The --tag argument tells parallel to print the filename as a prefix whenever a message is printed, so that one can trace any errors to the file that produced them.

:::{code} bash parallel --tag -j 2 ocrmypdf '{}' 'output/{}' ::: *.pdf :::

OCRmyPDF automatically repairs PDFs before parsing and gathering information from them.

Directory trees

This will walk through a directory tree and run OCR on all files in place, and printing each filename in between runs:

:::{code} bash find . -name '*.pdf' -printf '%p\n' -exec ocrmypdf '{}' '{}' ; :::

This only runs one ocrmypdf process at a time. This variation uses find to create a directory list and parallel to parallelize runs of ocrmypdf, again updating files in place.

:::{code} bash find . -name '*.pdf' | parallel --tag -j 2 ocrmypdf '{}' '{}' :::

In a Windows batch file, use

:::{code} bat for /r %%f in (*.pdf) do ocrmypdf %%f %%f :::

With a Docker container, you will need to stream through standard input and output:

:::{code} bash find . -name '*.pdf' -print0 | xargs -0 | while read pdf; do pdfout=$(mktemp) docker run --rm -i jbarlow83/ocrmypdf - - <$pdf >$pdfout && cp $pdfout $pdf done :::

Sample script

This user contributed script also provides an example of batch processing.

:::{literalinclude} ../misc/batch.py

caption: misc/batch.py

:::

Synology DiskStations

Synology DiskStations (Network Attached Storage devices) can run the Docker image of OCRmyPDF if the Synology Docker package is installed. Attached is a script to address particular quirks of using OCRmyPDF on one of these devices.

At the time this script was written, it only worked for x86-based Synology products. It is not known if it will work on ARM-based Synology products. Further adjustments might be needed to deal with the Synology's relatively limited CPU and RAM.

:::{literalinclude} ../misc/synology.py

caption: misc/synology.py - Sample script for Synology DiskStations

:::

Huge batch jobs

If you have thousands of files to work with, contact the author. Consulting work related to OCRmyPDF helps fund this open source project and all inquiries are appreciated.

Hot (watched) folders

Watched folders with watcher.py

OCRmyPDF has a folder watcher called watcher.py, which is currently included in source distributions but not part of the main program. It may be used natively or may run in a Docker container. Native instances tend to give better performance. watcher.py works on all platforms.

Users may need to customize the script to meet their requirements.

:::{code} bash pip3 install ocrmypdf[watcher]

env OCR_INPUT_DIRECTORY=/mnt/input-pdfs
OCR_OUTPUT_DIRECTORY=/mnt/output-pdfs
OCR_OUTPUT_DIRECTORY_YEAR_MONTH=1
python3 watcher.py :::

:::{list-table} watcher.py environment variables

header-rows: 1

• • Environment variable
  • Description
• • OCR_INPUT_DIRECTORY
  • Set input directory to monitor (recursive)
• • OCR_OUTPUT_DIRECTORY
  • Set output directory (should not be under input)
• • OCR_ARCHIVE_DIRECTORY
  • Set archive directory for processed originals (should not be under input, requires OCR_ON_SUCCESS_ARCHIVE to be set)
• • OCR_ON_SUCCESS_DELETE
  • This will move the processed original file to OCR_ARCHIVE_DIRECTORY if the exit code is 0 (OK). Note that OCR_ON_SUCCESS_DELETE takes precedence over this option, i.e. if both options are set, the input file will be deleted.
• • OCR_OUTPUT_DIRECTORY_YEAR_MONTH
  • This will place files in the output in {output}/{year}/{month}/{filename}
• • OCR_DESKEW
  • Apply deskew to crooked input PDFs
• • OCR_JSON_SETTINGS
  • A JSON string specifying any other arguments for ocrmypdf.ocr, e.g. 'OCR_JSON_SETTINGS={"rotate_pages": true, "optimize": "3"}'.
• • OCR_POLL_NEW_FILE_SECONDS
  • Polling interval
• • OCR_LOGLEVEL
  • Level of log messages t :::

One could configure a networked scanner or scanning computer to drop files in the watched folder.

Watched folders with Docker

The watcher service is included in the OCRmyPDF Docker image. To run it:

:::{code} bash docker run
--volume :/input
--volume :/output
--volume :/processed
--env OCR_OUTPUT_DIRECTORY_YEAR_MONTH=1
--env OCR_ON_SUCCESS_ARCHIVE=1
--env OCR_DESKEW=1
--env PYTHONUNBUFFERED=1
--interactive --tty --entrypoint python3
jbarlow83/ocrmypdf
watcher.py :::

This service will watch for a file that matches /input/\*.pdf, convert it to a OCRed PDF in /output/, and move the processed original to /processed. The parameters to this image are:

:::{list-table} Watcher Docker Parameters :header-rows: 1

• • Parameter
  • Description
• • --volume <path to files to convert>:/input
  • Files placed in this location will be OCRed
• • --volume <path to store results>:/output
  • This is where OCRed files will be stored
• • --volume <path to store processed originals>:/processed
  • Archive processed originals here
• • --env OCR_OUTPUT_DIRECTORY_YEAR_MONTH=1
  • Define environment variable OCR_OUTPUT_DIRECTORY_YEAR_MONTH=1 to place files in the output in {output}/{year}/{month}/{filename}
• • --env OCR_ON_SUCCESS_ARCHIVE=1
  • Define environment variable OCR_ON_SUCCESS_ARCHIVE to move processed originals
• • --env OCR_DESKEW=1
  • Define environment variable OCR_DESKEW to apply deskew to crooked input PDFs
• • --env PYTHONBUFFERED=1
  • This will force STDOUT to be unbuffered and allow you to see messages in docker logs :::

This service relies on polling to check for changes to the filesystem. It may not be suitable for some environments, such as filesystems shared on a slow network.

A configuration manager such as Docker Compose could be used to ensure that the service is always available.

:::{literalinclude} ../misc/docker-compose.example.yml

caption: misc/docker-compose.example.yml

:::

Caveats

• watchmedo may not work properly on a networked file system, depending on the capabilities of the file system client and server.
• This simple recipe does not filter for the type of file system event, so file copies, deletes and moves, and directory operations, will all be sent to ocrmypdf, producing errors in several cases. Disable your watched folder if you are doing anything other than copying files to it.
• If the source and destination directory are the same, watchmedo may create an infinite loop.
• On BSD, FreeBSD and older versions of macOS, you may need to increase the number of file descriptors to monitor more files, using ulimit -n 1024 to watch a folder of up to 1024 files.

Alternatives

• On Linux, systemd user services can be configured to automatically perform OCR on a collection of files.
• Watchman is a more powerful alternative to watchmedo.

macOS Automator

You can use the Automator app with macOS, to create a Workflow or Quick Action. Use a Run Shell Script action in your workflow. In the context of Automator, the PATH may be set differently your Terminal's PATH; you may need to explicitly set the PATH to include ocrmypdf. The following example may serve as a starting point:

You may customize the command sent to ocrmypdf.