Optical Character Recognition OCR technology got better and better over the past decades thanks to more elaborated algorithms, more CPU power and advanced machine learning methods. If you are in the midst of setting up an OCR solution and want to know how to increase the accuracy levels of your OCR engine, keep on reading … In this article, we cover different techniques to improve OCR accuracy and share our takeaways from building a world-class OCR system for Docparser.
In most cases, the accuracy in OCR technology is judged upon character level. How accurate an OCR software is on a character level depends on how often a character is recognized correctly versus how often a character is recognized incorrectly. While an accuracy of Measuring OCR accuracy is done by taking the output of an OCR run for an image and comparing it to the original version of the same text. You can then either count how many characters were detected correctly character level accuracyor count how many words were recognized correctly word level accuracy.
To improve word level accuracy, most OCR engines make use of additional knowledge regarding the language used in a text. If the language of the text is known e. Englishthe recognized words can be compared to a dictionary of all existing words e. In this article we will focus on improving the accuracy on character level. If the quality of the original source image is good, i. But if the original source itself is not clear, then OCR results will most likely include errors. The better the quality of original source image, the easier it is to distinguish characters from the rest, the higher the accuracy of OCR will be.
An OCR engine is the software which actually tries to recognize text in whatever image is provided. While many OCR engines are using the same type of algorithms, each of them comes with its own strengths and weaknesses. At the moment of writing it seems that Tesseract is considered the best open source OCR engine.
The Tesseract OCR accuracy is fairly high out of the box and can be increased significantly with a well designed Tesseract image preprocessing pipeline. Furthermore, the Tesseract developer community sees a lot of activity these days and a new major version Tesseract 4. The accuracy of Tesseract can be increased significantly with the right Tesseract image preprocessing toolchain. This leaves us with one single moving part in the equation to improve accuracy of OCR: The quality of the source image.Your message:.
The main advantage of tesseract-ocr is its high accuracy of character recognition. Tesseract is very good at recognizing multiple languages and fonts. It worked well and we did not spent much time on development. You also need these applications:. So one of my files looked like this:. Once they are all gathered in one place and named correctly, we need to generate the box files for them. These files tell Tesseract where each glyph is located.
Just open the bash console on Windows it would be cygwin and launch the script:. In this case, we are using two of them:.
This is the script I used. Do not run it now, read it carefully. The most important part of the script begins after that. We need to remove all the files generated last time if we run the script again.
Rename the files Now we have to add the language prefix to the generated files, so that they can be nicely consumed in the last step. Combine it all into a traineddata file And the last step.
Take all the files with pol. How to prepare training files for Tesseract OCR and improve characters recognition? What do we need before we begin? Uncomment this line if, you're rerunning the script rm pol. Uncomment this line if, you're rerunning the script.The method of extracting text from images is also called Optical Character Recognition OCR or sometimes simply text recognition.
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Tesseract was developed as a proprietary software by Hewlett Packard Labs. Since it has been actively developed by Google and many open source contributors.
Tesseract acquired maturity with version 3. Tesseract 3. In the past few years, Deep Learning based methods have surpassed traditional machine learning techniques by a huge margin in terms of accuracy in many areas of Computer Vision.
Handwriting recognition is one of the prominent examples. So, it was just a matter of time before Tesseract too had a Deep Learning based recognition engine.
Tesseract library is shipped with a handy command line tool called tesseract. We can use this tool to perform OCR on images and the output is stored in a text file.
The usage is covered in Section 2but let us first start with installation instructions. Later in the tutorial, we will discuss how to install language and script files for languages other than English. Tesseract 4 is included with Ubuntu Due to certain dependencies, only Tesseract 3 is available from official release channels for Ubuntu versions older than If you have an Ubuntu version other than these, you will have to compile Tesseract from source.
We will use Homebrew to install Tesseract on Homebrew. By default, Homebrew installs Tesseract 3, but we can nudge it to install the latest version from the Tesseract git repo using the following command. In the very basic usage, we specify the following. The language is chosen to be English and the OCR engine mode is set to 1 i. LSTM only.Our project managers and engineers can take over your existing project and bring new life to your business.
Over the years, Tesseract has been one of the most popular open source optical character recognition OCR solutions. It provides ready-to-use models for recognizing text in many languages. Currently there are models that are available to be downloaded and used.
Not too long ago, the project moved in the direction of using more modern machine-learning approaches and is now using artificial neural networks. For some people, this move meant a lot of confusion when they wanted to train their own models. This blog post tries to explain the process of turning scans of images with textual ground-truth data into models that are ready to be used.
You can download the pre-created ones designed to be fast and consume less memoryas well as the ones requiring more in terms of resources but giving a better accuracy. Pre-trained models have been created using the images with text artificially rendered using a huge corpus of text coming from the web.
The text was rendered using different fonts. For Latin-based languages, the existing model data provided has been trained on about textlines spanning about fonts. For other scripts, not so many fonts are available, but they have still been trained on a similar number of textlines.
Improve OCR Accuracy With Advanced Image Preprocessing
This blog post talks specifically about the latest version 4 of Tesseract. Please make sure that you have that installed and not some older version 3 release. While the image files are easy to prepare, the box files seem to be a source of confusion. You need to give them the same prefixes, e. The box files describe used characters as well as their spatial location within the image.
The order of characters is extremely important here. They should be sorted strictly in the visual order, going from left to right. Tesseract does the Unicode bidi-re-ordering internally on its own.Anti-integrin alpha v beta 3 antibody
It works best for me to set a 1x1 small rectangle as a bounding box that directly follows the previous character. Trying to make it choose out the whole Unicode set would be computationally unfeasible. This is what the so-called unicharset file is for. It defines the set of graphemes along with providing info about their basic properties. I came up with my own script in Ruby which compiles a very basic version of that file and is more than enough:.
The usage is as it stands in the source code:. Where do we get the all-boxes file from? The script only cares about the unique set of characters from the box files. The following gist of shell-work will provide you with all you need:. Make sure that you have Tesseract with langdata and tessdata properly installed.
If you keep your tessdata folder in a nonstandard location, you might need to either export or set inline the following shell variable:.How To Read Images in Java Using OCR- Tesseract
Notice the use of sort -R which makes the list sorted randomly which is a good practice when preparing the training data in many cases. Next, we want to create the list. Training and evaluation are interleaved. The former adjusts the neural network learnable parameters to minimize the so-called loss. The evaluation here is strictly to enhance the user experience: it prints out accuracy metrics periodically, letting you know how much the model has learned so far. Their values are averaged out.Tesseract 3.
Training with Tesseract
This page describes the training process, provides some guidelines on applicability to various languages, and what to expect from the results. Please check the list of languages for which traineddata is already available as of release 3. Tesseract was originally designed to recognize English text only. Efforts have been made to modify the engine and its training system to make them able to deal with other languages and UTF-8 characters.
Tesseract currently handles scripts like Arabic and Hindi with an auxiliary engine called cube included in Tesseract 3. Tesseract needs to know about different shapes of the same character by having different fonts separated explicitly. The number of fonts is limited to 64 fonts. Note that runtime is heavily dependent on the number of fonts provided, and training more than 32 will result in a significant slow-down.
For versions 3. The naming convention is languagecode. The files used for English 3. The traineddata file is simply a concatenation of the input files, with a table of contents that contains the offsets of the known file types. NOTE the files in the traineddata file are different from the list used prior to 3.
Text input files lang. You must create unicharsetinttempnormprotopffmtable using the procedure described below. If you are only trying to recognize a limited range of fonts like a single font for instancethen a single training page might be enough.
The other files no longer need to be provided, but will most likely improve accuracy, depending on your application. Some of the procedure is inevitably manual.
As much automated help as possible is provided.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. In TrainingTesseract 4.
I want to train Persian language in tesseract 4 lstm. I have some images from ancient manuscripts and I want to train with images and texts instead of font. I know that the old format box files will not work for LSTM training. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
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Is there a way to train tesseract to recognize a limited amount of text from an image. I am making a small app that recognizes a printed list of topics and so far using the tess-two library, tesseract does not fully recognize any of the text in the image. I am quite new to OCR so I'm not sure how to make this work. So far all the training instructions I've seen require a font file which I don't have. All I have are different images of the printed text. Hi, for me it helps often to upscale a image.
This brings quite good results. In case that you use screenshots, please notice, that screenshots usually have 72dpi, which is not sufficient for Tesseract.
There is a minimum text size for reasonable accuracy.
You have to consider resolution as well as point size. Accuracy drops off below 10pt x dpi, rapidly below 8pt x dpi. A quick check is to count the pixels of the x-height of your characters. X-height is the height of the lower case x.
At 10pt x dpi x-heights are typically about 20 pixels, although this can vary dramatically from font to font. Below an x-height of 10 pixels, you have very little chance of accurate results, and below about 8 pixels, most of the text will be "noise removed". Wikinautwhy do you link to the old wiki at googlecode instead to the new one at github? Please use tesseract user forum for support.
Also do not forget to search forum for you topic before asking for help.
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