OCRmyPDF/docs/batch.rst

.. 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 <https://www.gnu.org/software/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-block:: 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-block:: bash

   find . -printf '%p\n' -name '*.pdf' -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-block:: bash

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

In a Windows batch file, use

.. code-block:: 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-block:: 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 <https://www.synology.com/en-global/dsm/packages/Docker>`__ 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-block:: 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

.. csv-table:: watcher.py environment variables
    :header: "Environment variable", "Description"
    :widths: 50, 50

    "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 delete the input file if the exit code is 0 (OK). Mutually exclusive with ``OCR_ARCHIVE_DIRECTORY``."
    "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}'``."
    "OCR_POLL_NEW_FILE_SECONDS", "Polling interval"
    "OCR_LOGLEVEL", "Level of log messages to report"

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-block:: bash

    docker run \
        --volume <path to files to convert>:/input \
        --volume <path to store results>:/output \
        --volume <path to store processed originals>:/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:

.. csv-table:: watcher.py parameters for Docker
    :header: "Parameter", "Description"
    :widths: 50, 50

    "``--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_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
    :language: yaml
    :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 <https://wiki.archlinux.org/index.php/Systemd/User>`__
   can be configured to automatically perform OCR on a collection of files.

-  `Watchman <https://facebook.github.io/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:

.. figure:: images/macos-workflow.png
    :alt: Example macOS Automator workflow

You may customize the command sent to ocrmypdf.