text: #include "opencv2/core/utility.hpp"
  #include "opencv2/imgproc.hpp"
  #include "opencv2/imgcodecs.hpp"
  #include "opencv2/highgui.hpp"
  
  #include <iostream>
  
  using namespace cv;
  using namespace std;
  
  int _brightness = 100;
  int _contrast = 100;
  
  Mat image;
  
  /* brightness/contrast callback function */
  static void updateBrightnessContrast( int /*arg*/, void* )
  {
      int histSize = 64;
      int brightness = _brightness - 100;
      int contrast = _contrast - 100;
  
      /*
       * The algorithm is by Werner D. Streidt
       * (http://visca.com/ffactory/archives/5-99/msg00021.html)
       */
      double a, b;
      if( contrast > 0 )
      {
          double delta = 127.*contrast/100;
          a = 255./(255. - delta*2);
          b = a*(brightness - delta);
      }
      else
      {
          double delta = -128.*contrast/100;
          a = (256.-delta*2)/255.;
          b = a*brightness + delta;
      }
  
      Mat dst, hist;
      image.convertTo(dst, CV_8U, a, b);
      imshow("image", dst);
  
      calcHist(&dst, 1, 0, Mat(), hist, 1, &histSize, 0);
      Mat histImage = Mat::ones(200, 320, CV_8U)*255;
  
      normalize(hist, hist, 0, histImage.rows, NORM_MINMAX, CV_32F);
  
      histImage = Scalar::all(255);
      int binW = cvRound((double)histImage.cols/histSize);
  
      for( int i = 0; i < histSize; i++ )
          rectangle( histImage, Point(i*binW, histImage.rows),
                     Point((i+1)*binW, histImage.rows - cvRound(hist.at<float>(i))),
                     Scalar::all(0), -1, 8, 0 );
      imshow("histogram", histImage);
  }
  static void help()
  {
      std::cout << "\nThis program demonstrates the use of calcHist() -- histogram creation.\n"
                << "Usage: \n" << "demhist [image_name -- Defaults to ../data/baboon.jpg]" << std::endl;
  }
  
  const char* keys =
  {
      "{help h||}{@image|../data/baboon.jpg|input image file}"
  };
  
  int main( int argc, const char** argv )
  {
      CommandLineParser parser(argc, argv, keys);
      if (parser.has("help"))
      {
          help();
          return 0;
      }
      string inputImage = parser.get<string>(0);
  
      // Load the source image. HighGUI use.
      image = imread( inputImage, 0 );
      if(image.empty())
      {
          std::cerr << "Cannot read image file: " << inputImage << std::endl;
          return -1;
      }
  
      namedWindow("image", 0);
      namedWindow("histogram", 0);
  
      createTrackbar("brightness", "image", &_brightness, 200, updateBrightnessContrast);
      createTrackbar("contrast", "image", &_contrast, 200, updateBrightnessContrast);
  
      updateBrightnessContrast(0, 0);
      waitKey();
  
      return 0;
  }
  