Tesseract OCR with C++, OpenCV, and wxWidgets

Tesseract is a free optical character recognition software and it is considered one of the most accurate open-source OCR engines [1].

• Installation on Ubuntu
• Using tesseract command
• Tesseract C++ API with OpenCV
• With wxWidgets

Installation on Ubuntu

Tesseract is available directly on Ubuntu and you can install Tesseract and its development tools as follows [2].

$ sudo apt install tesseract-ocr
$ sudo apt install libtesseract-dev 

If you want to install language, you can use 'sudo apt install tesseract-ocr-[lang]'. For example, to install Myanmar language, use the following command.

$ sudo apt install tesseract-ocr-mya
$ tesseract --list-langs

Using tesseract command

To input the scanned image 'engim.jpg' and output the result to 'oute.txt' using English language, you can use the following command.

$ tesseract -l eng engim.jpg oute

Similarly, for Myanmar language, using 'myaim.jpg' as input, [3]

$ tesseract -l mya myaim.jpg outm

Tesseract C++ API with OpenCV

The following C++ example,ta.cpp, demonstrates using Tesseract API with OpenCV [4, 5]. For that, you need to install OpenCV as well. Please visit to the following link to see more details about installing OpenCV on Linux.

http://cool-emerald.blogspot.com/2017/11/opencv-on-linux-using-g-cmake-qt.html,

#include <tesseract/baseapi.h>
#include <leptonica/allheaders.h>
#include <opencv2/opencv.hpp>
using namespace cv;
int main()
{
    char *otxt;
    tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();

    // initialize tesseract-ocr with English
    if(api->Init(NULL,"eng")){
        fprintf(stderr,"Could not initialize tesseract.\n");
        exit(1);
    }

    // Open input image with OpenCV
    Mat img = imread("./engim.jpg",1);
    if(!img.data){
        fprintf(stderr,"Could not read input image.\n");
        exit(1);
    }

    // set image
    api->SetImage(img.data,img.cols,img.rows,3,img.step);

    // Get OCR result
    otxt = api->GetUTF8Text();
    printf("OCR output: \n%s\n",otxt);

    // destroy used obj and release memory
    api->End();
    delete api;
    delete [] otxt;

    return 0;
}

Use the following commands to build and run the program. The input image 'engim.jpg' should be in the same directory.

$ g++ ta.cpp `pkg-config --cflags --libs tesseract opencv` -o ta 
$ ./ta

With wxWidgets

An example C++ program, tawxcv.cpp, using Tesseract together with OpenCV and wxWidgets can be found at the following link.

https://github.com/yan9a/cewx/tree/master/tawxcv,

You need wxWidgets for the program and details about setting up wxWidgets can be found at the following link.

http://cool-emerald.blogspot.com/2013/08/cross-platform-c-programming-with.html,

To build the program using CMake and run, use the following commands.

$ cmake . 
$ make
$ ./tawxcv

The output of the program is illustrated below.

Figure. GUI of tawxcv.cpp

Acknowledgement

Thanks to my colleague, Ada, for introducing Tesseract to me.

References

[1] Wikipedia. Tesseract (software).
url: https://en.wikipedia.org/wiki/Tesseract_(software).

[2] Tesseract-OCR. Wiki page on GitHub.
url: https://github.com/tesseract-ocr/tesseract/wiki.

[3] Tesseract-OCR. Tesseract Manual Page.
url: https://github.com/tesseract-ocr/tesseract/blob/master/doc/tesseract.1.asc#languages.

[4] tessdoc. Tesseract documentation - API examples.
url: https://tesseract-ocr.github.io/tessdoc/APIExample.

[5] Evans Ehiorobo. Basic OCR with Tesseract and OpenCV.
url: https://medium.com/building-a-simple-text-correction-tool/basic-ocr-with-tesseract-and-opencv-34fae6ab3400.