title: OpenCv Aruco marker is not detected when i parse the Mat directly
body: <p>Hope you can help me out. I try to use Aruco marker for finding the corners of an Window. So added an marker to each corner. But when i tried to detected the marker they don't get found. If it take a photo with an smartphone and then try to detect the marker on the Photo it works. Here is a minimum working Code example:</p>
  
  <pre><code>#include &lt;opencv2/opencv.hpp&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string&gt; 
  #include &lt;opencv2/aruco.hpp&gt;
  using namespace cv;
  using namespace std;
  using namespace aruco;
  
  Dictionary dictionary;
  int markerSize = 200;
  vector&lt;int&gt; ids;
  vector&lt; vector&lt;Point2f&gt; &gt; corners;
  
  
  Mat addMarkertoImage(const Mat image){
      Mat retImage, marker0;
      image.copyTo(retImage);
      drawMarker(dictionary, 0, markerSize, marker0, 1);
  
      unsigned char value;
  
      //Add marker to top left corner
      for(int i = 0; i&lt;marker0.rows; i++)
        for(int j = 0; j&lt;marker0.cols; j++){
          value = marker0.at&lt;uchar&gt;(i,j);
          Vec3b colorValue = Vec3b(value, value, value);
          retImage.at&lt;Vec3b&gt;(i,j) = colorValue;} 
   return retImage;
   }
  
  
  int main(){
          Mat image, image_marker;
  dictionary = getPredefinedDictionary(cv::aruco::DICT_6X6_250); 
  image = imread( "bild.jpg", 1 );
  image_marker = addMarkertoImage(image);
  detectMarkers(image_marker, dictionary, corners, ids);
  drawDetectedMarkers(image_marker, corners, ids);
      imshow("Display Image", image_marker);
    waitKey(0);
    return 0;
  }
  </code></pre>
  
  <p>Any Ideas, why this does not work? But with an Photo taken by my iPhone camera is working?</p>