title: Make histogram graph using 3 channel using opencv
body: <p>I tried to plot histogram of a 3 channel image and "Unhandled exception at 0x752e812f in opencv_tut.exe: Microsoft C++ exception: cv::Exception at memory location 0x0019ef5c.." it keep getting this error. Cant even debug it keep getting into assembly.</p>
  
  <p>The problem is in the line drawing part in the histogram others just works fine.</p>
  
  <p>Here is the code:</p>
  
  <p>void colorHistogram(){</p>
  
  <pre><code>Mat image = imread("c:/aaa.jpg");
  vector&lt;Mat&gt; bgr_planes;
  split(image, bgr_planes);
  
  if(!image.data){
  
      cout&lt;&lt;"No image"&lt;&lt;endl;
  
  }
  
  int histSize = 256;
  float range[] = {0, 256};
  const float* histRange = {range};
  
  Mat b_hist, g_hist, r_hist;
  
  calcHist(&amp;bgr_planes[0], 1, 0, Mat(), b_hist, 1, &amp;histSize, &amp;histRange, true, false);
  calcHist(&amp;bgr_planes[1], 1, 0, Mat(), g_hist, 1, &amp;histSize, &amp;histRange, true, false); 
  calcHist(&amp;bgr_planes[2], 1, 0, Mat(), r_hist, 1, &amp;histSize, &amp;histRange, true, false); 
  
  int hist_w = 512;
  int hist_h = 400;
  
  int bin_w = cvRound((double) hist_w/histSize);
  
  Mat histImage(hist_h, hist_w, CV_8UC3, Scalar(0,0,0));
  
  normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
  normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
  normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
  
  for(int i=0; i&lt;histSize; i++){
  
    line( histImage, Point( bin_w*(i-1), hist_h - cvRound(b_hist.at&lt;float&gt;(i-1))) , Point( bin_w*(i), hist_h - cvRound(b_hist.at&lt;float&gt;(i))), Scalar( 255, 0, 0), 2, 8, 0  );
    line( histImage, Point( bin_w*(i-1), hist_h - cvRound(g_hist.at&lt;float&gt;(i-1))), Point( bin_w*(i), hist_h - cvRound(g_hist.at&lt;float&gt;(i))), Scalar( 0, 255, 0), 2, 8, 0  );
    line( histImage, Point( bin_w*(i-1), hist_h - cvRound(r_hist.at&lt;float&gt;(i-1))) , Point( bin_w*(i), hist_h - cvRound(r_hist.at&lt;float&gt;(i))), Scalar( 0, 0, 255), 2, 8, 0  );
  
  }
  
  namedWindow("Histogram", CV_WINDOW_AUTOSIZE);
  imshow("Histogram", histImage);
  </code></pre>
  
  <p>}</p>