ocrmypdf Documentation

CHAPTER

7

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 all ocrmypdf all files named *.pdf in the current directory and write them to the previous 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.

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

Directory trees

This will walk through a directory tree and run OCR on all files in place, printing the output in a way that makes find . --printf '%p' -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.

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

37

ocrmypdf Documentation, Release 5.2

Sample script

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

#!/usr/bin/env python3

# Walk through directory tree, replacing all files with OCR'd version

# Contributed by DeliciousPickle@github

import logging import os import subprocess import sys

script_dir = os .

path .

dirname(os .

path .

realpath( __file__ ))

print

(script_dir + '/ocr-tree.py: Start' )

if

len (sys .

argv) > 1 : start_dir = sys .

argv[ 1 ]

else

: start_dir = '.'

if

len (sys .

argv) > 2 : log_file = sys .

argv[ 2 ]

else

: log_file = script_dir + '/ocr-tree.log' logging .

basicConfig( level = logging .

INFO, format = ' %(asctime)s %(message)s ' , filename = log_file, filemode = 'w' )

for

dir_name, subdirs, file_list

in

os .

walk(start_dir): logging .

info( '\n' ) logging .

info(dir_name + '\n' ) os .

chdir(dir_name)

for

filename

in

file_list: file_ext = os .

path .

splitext(filename)[ 1 ]

if

file_ext == '.pdf' : full_path = dir_name + '/' + filename

print

(full_path) cmd = [ "ocrmypdf" , "--deskew" , filename, filename] logging .

info(cmd) proc = subprocess .

Popen( cmd, stdout = subprocess .

PIPE, stderr = subprocess .

STDOUT) result = proc .

stdout .

read()

if

proc .

returncode == 6 :

print

( "Skipped document because it already contained text" )

elif

proc .

returncode == 0 :

print

( "OCR complete" ) logging .

info(result)

API

OCRmyPDF is currently supported as a command line interface. Due to limitations in one of the libraries OCRmyPDF depends on, it is not yet usable as an API.

38 Chapter 7. Batch processing

ocrmypdf Documentation, Release 5.2

Huge batch jobs

If you have thousands of files to work with, contact the author.

Hot (watched) folders

To set up a “hot folder” that will trigger OCR for every file inserted, use a program like Python watchdog (supports all major OS).

One could then configure a scanner to automatically place scanned files in a hot folder, so that they will be queued for

OCR and copied to the destination.

pip install watchdog watchdog installs the command line program watchmedo, which can be told to run ocrmypdf on any .pdf added to the current directory (.) and place the result in the previously created out/ folder.

cd hot-folder mkdir out watchmedo shell-command

\

--patterns = "*.pdf" \

--ignore-directories

\

--command = 'ocrmypdf "${watch_src_path}" "out/${watch_src_path}" ' \

.

# don't forget the final dot

For more complex behavior you can write a Python script around to use the watchdog API.

On file servers, you could configure watchmedo as a system service so it will run all the time.

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

• Watchman is a more powerful alternative to watchmedo.

7.3. Hot (watched) folders 39

ocrmypdf Documentation, Release 5.2

40 Chapter 7. Batch processing