title: OpenCV SIFT extractor failing
body: <p>I am getting the following error while executing my code:(OpenCV with Qt Creator)</p>
  
  <blockquote>
    <p>OpenCV Error: Assertion failed (!outImage.empty()) in drawKeypoints,file C:\Ope nCV\opencv\modules\features2d\src\draw.cpp, line 115
    C:\OpenCV\opencv\modules\features2d\src\draw.cpp:115: error: (-215) !outImage.em pty() in function drawKeypoints</p>
  </blockquote>
  
  <p>Code:</p>
  
  <pre><code>#include &lt;QCoreApplication&gt;
  #include &lt;iostream&gt;
  
  #include "opencv2/core/core.hpp"
  #include "opencv2/highgui/highgui.hpp"
  #include "opencv/cv.h"
  #include &lt;opencv2/nonfree/features2d.hpp&gt;
  
  using namespace std;
  using namespace cv;
  
  int main(int argc, char *argv[])
  {
     // QCoreApplication a(argc, argv);
      cout &lt;&lt; "Hello World!" &lt;&lt; endl;
  
      try {
      cv::Mat image = cv::imread("lena.jpg",0);
      // Create smart pointer for SIFT feature detector.
       cv::Ptr&lt;FeatureDetector&gt; featureDetector = cv::FeatureDetector::create("SIFT");
       cv::vector&lt;KeyPoint&gt; keypoints;
  
       // Detect the keypoints
       featureDetector-&gt;detect(image, keypoints); // NOTE: featureDetector is a pointer hence the '-&gt;'.
  
       //Similarly, we create a smart pointer to the SIFT extractor.
       cv::Ptr&lt;DescriptorExtractor&gt; featureExtractor = cv::DescriptorExtractor::create("SIFT");
  
       // Compute the 128 dimension SIFT descriptor at each keypoint.
       // Each row in "descriptors" correspond to the SIFT descriptor for each keypoint
       cv::Mat descriptors;
       featureExtractor-&gt;compute(image, keypoints, descriptors);
  
       // If you would like to draw the detected keypoint just to check
       cv::Mat outputImage;
       cv::Scalar keypointColor = cv::Scalar(255, 0, 0);     // Blue keypoints.
       drawKeypoints(image, keypoints, outputImage, keypointColor, cv::DrawMatchesFlags::DEFAULT);
  
       cvNamedWindow("Output");
       cv::imshow("Output", outputImage);
  
       char c = ' ';
       cvWaitKey(0);
  
      }
      catch(cv::Exception e)
      {
          cout&lt;&lt; e.msg;
      }
  
      return 0;
  }
  </code></pre>
  
  <p>contents of the .pro file</p>
  
  <blockquote>
  <pre><code> INCLUDEPATH += "C:\\OpenCV\\opencv\\build\\x64\\mingw\\bin\\install\\include" \
                     "C:\\OpenCV\\opencv\\build\\x64\\mingw\\bin\\install\\include\\opencv"
  </code></pre>
    
    <p>\
                           "C:\OpenCV\opencv\build\x64\mingw\bin\install\include\opencv2"</p>
  
  <pre><code>    LIBS += -L"C:\\OpenCV\\opencv\\build\\x64\\mingw\\bin\\install\\lib" \
          -lopencv_core244d \
          -lopencv_highgui244d \
          -lopencv_imgproc244d \
          -lopencv_features2d244d \
          -lopencv_nonfree244d
  </code></pre>
  </blockquote>
  
  <p>I have checked that lena.jpg is present in the working directory</p>