title: Opencv: Create black window and write text to it
body: <p>Is there a simple way to create a black image file and write text to it?  I have tried  simply creating a Mat using </p>
  
  <p><code>cv::Mat pic = cv::Mat::zeros(250,250,CV_8U)</code></p>
  
  <p>and then write text to it using the command </p>
  
  <p><code>cv::putText(pic, "some text",cv::Point(50,50), CV_FONT_HERSHEY_SIMPLEX, 0.5,          cv::Scalar(0,0,255,0),1,8,false);</code></p>
  
  <p>Do I need a different type instead of <code>CV_8U</code> in my initial matrix of zeros?  Or am I missing something else here?</p>
  
  <p>Thanks</p>