#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

int main ( int argc, char **argv )
{
   Mat im_gray = imread("img3.jpg",CV_LOAD_IMAGE_GRAYSCALE);

   Mat im_rgb  = imread("img3.jpg");
   cvtColor(im_rgb,im_gray,CV_RGB2GRAY);

   Mat img_bw = im_gray > 115;

   imwrite("img_bw3.jpg", img_bw);

   return 0;
}

cvThreshold(scr, dst, 128, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);

cv::threshold(im_gray, img_bw, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);