title: OpenCV imwrite is not working
body: <p>I have a simple OpenCV application that takes a video stream from the webcam, and when the <code>spacebar</code> is pressed it captures the current image and freezes on that image. When I try to use the <code>cv::imwrite()</code> method to save the picture to disk, it does not work. The code successfully compiles but it does not save the image. It is returning a false value as well from the call. I am not sure if this is an issue of type of image or something else, but I seem to be stumped.</p>
  
  <p>Here is the code for my current cpp class:</p>
  
  <pre><code>#include &lt;iostream&gt;
  
  #include "opencv2/imgproc/imgproc.hpp"
  #include "opencv2/highgui/highgui.hpp"
  
  using namespace std;
  using namespace cv;
  
  Mat picture;
  char key;
  
  class FacialRec {
  
  };
  
  int main() {
      //Starting the video
      VideoCapture videoCapture(0);
  
      if (!videoCapture.isOpened()) {
          cout &lt;&lt; "Unable to open video file." &lt;&lt; endl;
          return 1;
      }
  
      namedWindow("Webcam", CV_WINDOW_AUTOSIZE);
  
      while(true) {
          Mat frame;
          videoCapture.retrieve(frame);
          bool success = videoCapture.read(frame);
  
          if (!success) {
              cout &lt;&lt; "Could not read from video file" &lt;&lt; endl;
              return 1;
          }
  
          imshow("Webcam", frame);
          key = waitKey(30);
  
          if (key == 27) { //escape key pressed: stop program
              cout &lt;&lt; "ESC pressed. Program closing..." &lt;&lt; endl;
              break;
          }else if (key == ' ') { //spacebar pressed: take a picture
              picture = frame;
              key = -1;
  
              while (true) {
                  imshow("Webcam", picture);
  
                  key = waitKey(30);
  
                  if (key == 27 || key == 32) {
                      cout &lt;&lt; "ESC or SPACE pressed. Returning to video..." &lt;&lt; endl;
                      break;
                  }
  
                  if (key == 115) {
                      //trying to save to current directory
                      bool maybe = imwrite("/testimage.jpg", picture);
                      // maybe bool is always getting value of 0, or false
                     cout &lt;&lt; "s was pressed. saving image " &lt;&lt; maybe &lt;&lt; endl;
                  }   
              }
          }
  
      }
  
      return 0;
  }
  </code></pre>