Local Thresholding from Zxing Library (C++)

In this tutorial, I will go over how to call local threshold method in zxing library, ported to C++ (zxing-cpp) instead of Java. If you want to implement it in Java, refer to this tutorial. I will assume that OpenCV library is installed on the system.

First, one needs to download zxing-cpp
$ git clone https://github.com/glassechidna/zxing-cpp.git
$ mkdir build && cd build

To integrate zxing-cpp with system's OpenCV, one needs to first search for OpenCVConfig.cmake file:
$ find / -iname opencvconfig.cmake 2>/dev/null
/usr/local/Cellar/opencv3/3.2.0/share/OpenCV/OpenCVConfig.cmake

In my case, I installed OpenCV from Homebrew, and its config cmake file is in /usr/local/Cellar/opencv3/3.2.0/share/OpenCV/ directory. Export OpenCV_DIR environment variable to point to this path:
$ export OpenCV_DIR='/usr/local/Cellar/opencv3/3.2.0/share/OpenCV/'

Now, we are ready to compile and install:
$ cmake -G "Unix Makefiles" ..
$ make -j2
$ sudo make install

Next, change directory to your working directory and create zxing.cpp source file as below:

	#include <zxing/LuminanceSource.h>
	#include <zxing/Binarizer.h>
	#include <zxing/BinaryBitmap.h>
	#include <zxing/common/GlobalHistogramBinarizer.h>
	#include <zxing/MatSource.h>
	#include <opencv2/imgproc.hpp>
	#include <opencv2/imgcodecs.hpp>
	#include <opencv2/highgui.hpp>
	using namespace zxing;
	using namespace cv;
	int main( int argc, char** argv )
	{
	Mat img = imread(argv[1]);
	cvtColor(img, img, COLOR_BGR2GRAY);
	Ref<LuminanceSource> source = MatSource::create(img);
	Ref<Binarizer> binarizer(new GlobalHistogramBinarizer(source));
	Ref<BinaryBitmap> bitmap(new BinaryBitmap(binarizer));
	Ref<BitMatrix> bitMatrix = bitmap->getBlackMatrix();
	for (int row=0; row<bitMatrix->getHeight(); row++) {
	for (int col=0; col<bitMatrix->getWidth(); col++) {
	img.row(row).col(col) = bitMatrix->get(col, row) ? Scalar(255) : Scalar(0);
	}
	}
	cv::imshow("output", img);
	cv::waitKey();
	return 0;
	}

view raw zxing.cpp hosted with ❤ by GitHub

To compile, we first need to copy MatSource.h into zxing include directory. I am assuming that you have cloned the zxing-cpp repository into ~/zxing-cpp-master.
$ sudo cp ~/zxing-cpp-master/opencv/src/zxing/MatSource.h /usr/local/include/zxing/
where /usr/local/include/zxing is the folder that contains zxing-cpp library's header files.

We also need to locate where zxing-cpp library file is installed. You can look it up from the output after sudo make install command above, or search the file as shown below.
$ find / -name libzxing.a 2>/dev/null
/usr/local/lib/libzxing.a

Finally, we are ready to compile.
$ g++ zxing.cpp `pkg-config --libs opencv` -lzxing -L/usr/local/lib/

Make sure to replace /usr/local/lib/ above after -L option with the directory where libzxing.a file is installed in your system.

To execute, run the following:

$ ./a.out some_image.jpg

You should see local threshold binary image of your input image file.