03.08.2020       Выпуск 346 (03.08.2020 - 09.08.2020)       Статьи

Tesseract OCR for Non-English Languages

Читать>>




Экспериментальная функция:

Ниже вы видите текст статьи по ссылке. По нему можно быстро понять ссылка достойна прочтения или нет

Просим обратить внимание, что текст по ссылке и здесь может не совпадать.

In this tutorial, you will learn how to OCR non-English languages using the Tesseract OCR engine.

If you refer to my previous Optical Character Recognition (OCR) tutorials on the PyImageSearch blog, you’ll note that all of the OCR text is in the English language.

But what if you wanted to OCR text that was non-English?

What steps would you need to take?

And how does Tesseract work with non-English languages?

We’ll be answering all of those questions in this tutorial.

To learn how to OCR text in non-English languages using Tesseract, just keep reading.

Tesseract Optical Character Recognition (OCR) for Non-English Languages

In the first part of this tutorial you will learn how to configure the Tesseract OCR engine for multiple languages, including non-English languages.

I’ll then show you how you can download multiple language packs for Tesseract and verify that it works properly — we’ll use German as an example case.

From there, we will configure the TextBlob package, which will be used to translate from one language into another.

Once we have completed all of this setup, we’ll implement the Project Structure for a Python script that will:

  1. Accept an input image
  2. Detect and OCR text in non-English languages
  3. Translate the OCR’d text from the given input language into English
  4. Display the results to our terminal

Let’s get started!

Configuring Tesseract OCR for Multiple Languages

In this section, we are going to configure Tesseract OCR for multiple languages. We will break this down, step by step, to see what it looks like on both macOS and Ubuntu.

If you have not already installed Tesseract:

  • I have provided instructions for installing the Tesseract OCR engine as well as pytesseract (the Python bindings used to interface with Tesseract) in my blog post OpenCV OCR and text recognition with Tesseract.
  • Follow the instructions in the How to install Tesseract 4 section of that tutorial, confirm your Tesseract install, and then come back here to learn how to configure Tesseract for multiple languages.

Technically speaking, Tesseract should already be configured to handle multiple languages, including non-English languages; however, in my experience the multi-language support can be a bit temperamental. We are going to review my method that gives consistent results.

If you installed Tesseract on macOS via Homebrew, your Tesseract language packs should be available in /usr/local/Cellar/tesseract/<version>/share/tessdata where <version> is the version number for your Tesseract install (you can use the tab key to autocomplete to derive the full path on your machine).

If you are running on Ubuntu, your Tesseract language packs should be located in the directory /usr/share/tesseract-ocr/<version>/tessdata where <version> is the version number for your Tesseract install.

Let’s take a quick look at the contents of this tessdata directory with an ls command as shown in Figure 1, below, which corresponds to the Homebrew installation on my macOS for an English language configuration.

Figure 1: This is an example of a macOS Tesseract install with only the English language pack.

The only language pack installed in macOS Tesseract is English, which is contained in the eng.traineddata file.

  • eng.traineddata is the language pack for English.
  • osd.traineddata is a special data file related to orientation and scripts.
  • snum.traineddata is an internal serial number used by Tesseract.
  • pdf.ttf is a True Type Format Font file to support pdf renderings.

In the remainder of this section, I’ll share with you my recommended foolproof method to configure Tesseract for multiple languages. Then we’ll jump into the project structure and actual execution breakdowns.

Download and Add Language Packs to Tesseract OCR

Figure 2: You can see that Tesseract OCR supports a wide array of languages. In fact, Tesseract supports over 100 languages, including those that comprise characters and symbols, as well as right-to-left languages.

The first version of Tesseract provided support for the English language only. Support for French, Italian, German, Spanish, Brazilian Portuguese, and Dutch were added in the second version.

In the third version, support was dramatically expanded to include ideographic (symbolic) languages such as Chinese and Japanese as well as right-to-left languages such as Arabic and Hebrew.

The fourth version, which we are now using supports over 100 languages and has support for characters and symbols.

Note: The fourth version contains trained models for Tesseract’s legacy and newer, more accurate Long Short-Term Memory (LSTM) OCR engine.

Now that we have an idea of the breadth of supported languages, let’s dive in to see the most foolproof method I’ve found to configure Tesseract and unlock the power of this vast multi-language support:

  1. Download Tesseract’s language packs manually from GitHub and install them.
  2. Set the TESSDATA_PREFIX environment variable to point to the directory containing the language packs.

The first step here is to clone Tesseract’s GitHub tessdata repository, which is located here:

https://github.com/tesseract-ocr/tessdata

We want to move to the directory that we wish to be the parent directory for what will be our local tessdata directory. Then, we’ll simply issue the git command below to clone the repo to our local directory.

$ git clone https://github.com/tesseract-ocr/tessdata

Note: Be aware that at the time of this writing, the resultingtessdatadirectory will be ~4.85GB, so make sure you have ample space on your hard drive.

The second step is to set up the TESSDATA_PREFIX environment variable to point to the directory containing the language packs. We’ll change directory (cd) into the tessdata directory and use the pwd command to determine the full system path to the directory:

$ cd tessdata/
$ pwd
/Users/adrianrosebrock/Desktop/tessdata

Your tessdata directory will have a different path from mine, so make sure you run the above commands to determine the path specific to your machine!

From there, all you need to do is set the TESSDATA_PREFIX environment variable to point to your tessdata directory, thereby allowing Tesseract to find the language packs. To do that, simply execute the following command:

$ export TESSDATA_PREFIX=/Users/adrianrosebrock/Desktop/tessdata

Again, your full path will be different from mine, so take care to double-check and triple-check your file path.

Project Structure

Let’s review the project structure.

Once you grab the files from the “Downloads” section of this article, you’ll be presented with the following directory structure:

$ tree --dirsfirst --filelimit 10
.
├── images
│   ├── arabic.png
│   ├── german.png
│   ├── german_block.png
│   ├── swahili.png
│   └── vietnamese.png
└── ocr_non_english.py

1 directory, 6 files

The images/ sub-directory contains several PNG files that we will use for OCR. The titles indicate the native language that will be used for the OCR.

The Python file ocr_non_english.py, located in our main directory, is our driver file. It will OCR our text in its native language, and then translate from the native language into English.

Verifying Tesseract Support for Non-English Languages

At this point, you should have Tesseract correctly configured to support non-English languages, but as a sanity check, let’s validate that the TESSDATA_PREFIX environment variable is set correctly by using the echo command:

$ echo $TESSDATA_PREFIX
/Users/adrianrosebrock/Desktop/tessdata

Remember, your tessdata directory will be different from mine!

We should move from the tessdata directory to the project images directory so we can test non-English language support. We can do this by supplying the --lang or -l command line argument, specifying the language we want Tesseract to use when OCR’ing.

$ tesseract german.png stdout -l deu

Here, I am OCR’ing a file named german.png where the -l parameter indicates that I want Tesseract to OCR German text (deu).

To determine the correct three-letter country/region code for a given language, you should:

  1. Inspect the tessdata directory.
  2. Refer to the Tesseract documentation, which lists the languages and corresponding codes that Tesseract supports.
  3. Use this webpage to determine the country code for where a language is predominantly used.
  4. Finally, if you still cannot derive the correct country code, use a bit of Google-foo, and search for three-letter country codes for your region (it also doesn’t hurt to search Google for Tesseract <language name> code).

With a little bit of patience, along with some practice, you’ll be OCR’ing text in non-English languages with Tesseract.

Environmental Setup for the TextBlob Package

Now that we have Tesseract set up and have added support for a non-English language, we need to set up the TextBlob package.

Note: This step assumes that you are already working in a Python3 virtual environment (e.g.$ workon cvwherecvis the name of a virtual environment — yours will probably be different).

To install textblob is just one quick command:

$ pip install textblob

Great job setting up your environmental dependencies!

Implementing Our Tesseract with Non-English Languages Script

We are now ready to implement Tesseract for non-English language support. Let’s review the existing ocr_non_english.py from the downloads section.

Open up the ocr_non_english.py file in your project directory, and insert the following code:

# import the necessary packages
from textblob import TextBlob
import pytesseract
import argparse
import cv2

# construct the argument parser and parse the arguments
ap = argparse.ArgumentParser()
ap.add_argument("-i", "--image", required=True,
	help="path to input image to be OCR'd")
ap.add_argument("-l", "--lang", required=True,
	help="language that Tesseract will use when OCR'ing")
ap.add_argument("-t", "--to", type=str, default="en",
	help="language that we'll be translating to")
ap.add_argument("-p", "--psm", type=int, default=13,
	help="Tesseract PSM mode")
args = vars(ap.parse_args())

Line 5 imports TextBlob, which is a very useful Python library for processing textual data. It can perform various natural language processing tasks such as tagging parts of speech. We will use it to translate OCR’d text from a foreign language into English. You can read more about TextBlob here: https://textblob.readthedocs.io/en/dev/

We then import pytesseract, which is the Python wrapper for Google’s Tesseract OCR library (Line 6).

  • --image: The path to the input image to be OCR’d.
  • --lang: The native language that Tesseract will use when ORC’ing the image.
  • --to: The language into which we will be translating the native OCR text.
  • --psm: The page segmentation mode for Tesseract. Our default is for a page segmentation mode of 13, which treats the image as a single line of text. For our last example today, we will OCR a full block of text of German. For this full block, we will use a page segmentation mode of 3 which is fully automatic page segmentation without Orientation and Script Detection (OSD).

With our imports, convenience function, and command line args ready to go, we just have a few initializations to handle before we loop over frames:

# load the input image and convert it from BGR to RGB channel
# ordering
image = cv2.imread(args["image"])
rgb = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)

# OCR the image, supplying the country code as the language parameter
options = "-l {} --psm {}".format(args["lang"], args["psm"])
text = pytesseract.image_to_string(rgb, config=options)

# show the original OCR'd text
print("ORIGINAL")
print("========")
print(text)
print("")

In this section, we are going to load the image from a file, change the order of the color channels of the image, set the options for Tesseract, and perform optical character recognition on the image in its native language.

Line 24 loads the image using cv2.imread while on Line 25 swaps the color channels from Blue-Green-Red (BGR) to Red-Green-Blue (RGB) so the image is compatible with Tesseract, which takes an input image with an RGB color channel ordering.

From there, we supply the options for Tesseract (Line 28) which include:

  • The native language to be used by Tesseract to OCR the image (-l).
  • The Page Segmentation Mode option (-psm). These correspond to the input arguments that we supply on our command line when we run this program.

Next, we will wrap up this section by showing the OCR’d results from Tesseract in the native language (Lines 32-35):

# translate the text into a different language
tb = TextBlob(text)
translated = tb.translate(to=args["to"])

# show the translated text
print("TRANSLATED")
print("==========")
print(translated)

Now that we have the text OCR’d in the native language, we are going to translate the text from the native language specified by our --lang command line argument to the output language described by our --to command line argument.

We abstract the text to a textblob using TextBlob (Line 38). Then, we translate the final language on Line 39 using tb.tranlsate. We wrap up by printing the results of the translated text (Lines 42-44). Now you have a complete workflow that includes OCR’ing the text in the native language and translated it into your desired language.

Great job implementing Tesseract for different languages — it was relatively straightforward, as you can see. Next, we’ll ensure that our script and Tesseract are firing on all cylinders.

Tesseract OCR and Non-English Languages Results

It’s time for us to put Tesseract for non-English languages to work!

Open up a terminal, and execute the following command from the main project directory:

$ python ocr_non_english.py --image images/german.png --lang deu
ORIGINAL
========
Ich brauche ein Bier!

TRANSLATED
==========
I need a beer!
Figure 3: Tesseract OCR results for German can help you order your next beer.

In Figure 3, you can see an input image with the text “Ich brauche ein Bier!” which is German for “I need a beer!”

By passing in the --lang deu flag, we were able to tell Tesseract to OCR the German text, which we then translated to English.

Let’s try another example, this one with Swahili input text:

$ python ocr_non_english.py --image images/swahili.png --lang swa
ORIGINAL
========
Jina langu ni Adrian

TRANSLATED
==========
My name is Adrian
Figure 4: Tesseract OCR results for Swahili might help you communicate in Swahili on your next safari.

The --lang swa flag indicates that we want to OCR Swahili text (Figure 4).

Tesseract correctly OCR’s the text “Jina langu ni Adrian,” which when translated to English, is “My name is Adrian.”

This example shows how to OCR text in Vietnamese, which is a different script/writing system than the previous examples:

$ python ocr_non_english.py --image images/vietnamese.png --lang vie
ORIGINAL
========
Tôi mến bạn..

TRANSLATED
==========
I love you..
Figure 5: Tesseract is powerful enough to OCR languages like Vietnamese that have different scripts.

By specifying the --lang vie flag, Tesseract is able to successfully OCR the Vietnamese “Tôi mến bạn,” which translates to “I love you” in English.

$ python ocr_non_english.py --image images/arabic.png --lang ara
ORIGINAL
========
أنا أتحدث القليل من العربية فقط..

TRANSLATED
==========
I only speak a little Arabic ..
Figure 6: Tesseract can also OCR right-to-left languages like Arabic.

Using the --lang ara flag, we’re able to tell Tesseract to OCR Arabic text.

Here, we can see that the Arabic script “أنا أتحدث القليل من العربية فقط.” roughly translates to “I only speak a little Arabic” in English.

For our final example, let’s OCR a large block of German text:

$ python ocr_non_english.py --image images/german_block.png --lang deu --psm 3
ORIGINAL
========
Erstes Kapitel

Gustav Aschenbach oder von Aschenbach, wie seit seinem fünfzigsten
Geburtstag amtlich sein Name lautete, hatte an einem
Frühlingsnachmittag des Jahres 19.., das unserem Kontinent monatelang
eine so gefahrdrohende Miene zeigte, von seiner Wohnung in der Prinz-
Regentenstraße zu München aus, allein einen weiteren Spaziergang
unternommen. Überreizt von der schwierigen und gefährlichen, eben
jetzt eine höchste Behutsamkeit, Umsicht, Eindringlichkeit und
Genauigkeit des Willens erfordernden Arbeit der Vormittagsstunden,
hatte der Schriftsteller dem Fortschwingen des produzierenden
Triebwerks in seinem Innern, jenem »motus animi continuus«, worin
nach Cicero das Wesen der Beredsamkeit besteht, auch nach der
Mittagsmahlzeit nicht Einhalt zu tun vermocht und den entlastenden
Schlummer nicht gefunden, der ihm, bei zunehmender Abnutzbarkeit
seiner Kräfte, einmal untertags so nötig war. So hatte er bald nach dem
Tee das Freie gesucht, in der Hoffnung, daß Luft und Bewegung ihn
wieder herstellen und ihm zu einem ersprießlichen Abend verhelfen
würden.

Es war Anfang Mai und, nach naßkalten Wochen, ein falscher
Hochsommer eingefallen. Der Englische Garten, obgleich nur erst zart
belaubt, war dumpfig wie im August und in der Nähe der Stadt voller
Wagen und Spaziergänger gewesen. Beim Aumeister, wohin stillere und
stillere Wege ihn geführt, hatte Aschenbach eine kleine Weile den
volkstümlich belebten Wirtsgarten überblickt, an dessen Rande einige
Droschken und Equipagen hielten, hatte von dort bei sinkender Sonne
seinen Heimweg außerhalb des Parks über die offene Flur genommen
und erwartete, da er sich müde fühlte und über Föhring Gewitter drohte,
am Nördlichen Friedhof die Tram, die ihn in gerader Linie zur Stadt
zurückbringen sollte. Zufällig fand er den Halteplatz und seine
Umgebung von Menschen leer. Weder auf der gepflasterten
Ungererstraße, deren Schienengeleise sich einsam gleißend gegen
Schwabing erstreckten, noch auf der Föhringer Chaussee war ein
Fuhrwerk zu sehen; hinter den Zäunen der Steinmetzereien, wo zu Kauf

TRANSLATED
==========
First chapter

Gustav Aschenbach or von Aschenbach, like since his fiftieth
Birthday officially his name was on one
Spring afternoon of the year 19 .. that our continent for months
showed such a threatening expression from his apartment in the Prince
Regentenstrasse to Munich, another walk alone
undertaken. Overexcited by the difficult and dangerous, just
now a very careful, careful, insistent and
Accuracy of the morning's work requiring will,
the writer had the swinging of the producing
Engine inside, that "motus animi continuus", in which
according to Cicero the essence of eloquence persists, even after the
Midday meal could not stop and the relieving
Slumber not found him, with increasing wear and tear
of his strength once was necessary during the day. So he had soon after
Tea sought the free, in the hope that air and movement would find him
restore it and help it to a profitable evening
would.

It was the beginning of May and, after wet and cold weeks, a wrong one
Midsummer occurred. The English Garden, although only tender
leafy, dull as in August and crowded near the city
Carriages and walkers. At the Aumeister, where quiet and
Aschenbach had walked the more quiet paths for a little while
overlooks a popular, lively pub garden, on the edge of which there are a few
Stops and equipages stopped from there when the sun was down
made his way home outside the park across the open corridor
and expected, since he felt tired and threatened thunderstorms over Foehring,
at the northern cemetery the tram that takes him in a straight line to the city
should bring back. By chance he found the stopping place and his
Environment of people empty. Neither on the paved
Ungererstrasse, the rail tracks of which glisten lonely against each other
Schwabing extended, was still on the Föhringer Chaussee
See wagon; behind the fences of the stonemasons where to buy
Figure 7: Tesseract can scale to OCR whole pages such as this large block of German.

In just a few seconds, we were able to OCR the German text and then translate it to English.

So really, the biggest challenge OCR’ing non-English languages is configuring your tessdata and language packs — after that, OCR’ing non-English languages is as simple as setting the correct country/region/language code!

What’s Next?

Optical Character Recognition (OCR) is a simple concept but is hard in practice: create a piece of software that accepts an input image, have that software automatically recognize the text in the image, and then convert it to machine-encoded text (i.e., a “string” data type).

But despite being such an intuitive concept, OCR is incredibly hard. The field of computer vision has existed for over 50 years (with mechanical OCR machines dating back over 100 years), but we still have not “solved” OCR and created an off-the-shelf OCR system that works in nearly any situation.

And worse, trying to code custom software that can perform OCR is even harder:

  • Open source OCR packages like Tesseract can be difficult to use if you are new to the world of OCR.
  • Obtaining high accuracy with Tesseract typically requires that you know which options, parameters, and configurations to use — and unfortunately there aren’t many high-quality Tesseract tutorials or books online.
  • Computer vision and image processing libraries such as OpenCV and scikit-image can help you preprocess your images to improve OCR accuracy…but which algorithms and techniques do you use?
  • Deep learning is responsible for unprecedented accuracy in nearly every area of computer science. Which deep learning models, layer types, and loss functions should you be using for OCR?

If you’ve ever found yourself struggling to apply OCR to a project, or if you’re simply interested in learning OCR, my brand new book, OCR with OpenCV, Tesseract, and Python is for you.

Regardless of your current experience level with computer vision and OCR, after reading this book you will be armed with the knowledge necessary to tackle your own OCR projects.

If you’re interested in OCR, already have OCR project ideas/need for it at your company, or simply want to stay informed about our progress as we develop the book, please click the button below to stay informed. I’ll be sharing more with you soon!

Summary

In this blog post, you learned how to configure Tesseract to OCR non-English languages.

Most Tesseract installs will naturally handle multiple languages with no additional configuration; however, in some cases you will need to:

  1. Manually download the Tesseract language packs
  2. Set the TESSDATA_PREFIX environment variable to point the language packs
  3. Verify that the language packs directory is correct

Failure to complete the above three steps may prevent you from using Tesseract with non-English languages, so make sure you follow the steps in this tutorial closely!

Provided you do so, you shouldn’t have any issues OCR’ing non-English languages.

To download the source code to this post (and be notified when future tutorials are published here on PyImageSearch), simply enter your email address in the form below!

Download the Source Code and FREE 17-page Resource Guide

Enter your email address below to get a .zip of the code and a FREE 17-page Resource Guide on Computer Vision, OpenCV, and Deep Learning. Inside you’ll find my hand-picked tutorials, books, courses, and libraries to help you master CV and DL!






Разместим вашу рекламу

Пиши: mail@pythondigest.ru

Нашли опечатку?

Выделите фрагмент и отправьте нажатием Ctrl+Enter.

Система Orphus