title: How to link OpenCV 4 with ROS (cv_bridge)
body: <p>I'm using OpenCV in ROS Melodic, I need now to use cv::dnn (deep neural network), which is incluced in OpenCV 4, which I have installed, and set it to my CMakeLists.txt like this:</p>
  
  <pre><code>find_package(OpenCV 4 REQUIRED )
  </code></pre>
  
  <p>this is warning that I'm getting when I do command: <strong>catkin_make</strong> in my ros workspace:</p>
  
  <blockquote>
    <p>/usr/bin/ld: warning: libopencv_imgcodecs.so.3.2, needed by
    /opt/ros/melodic/lib/libcv_bridge.so, may conflict with
    libopencv_imgcodecs.so.4.1</p>
  </blockquote>
  
  <p>I ignored that but I can't rosrun any node with opencv right now.</p>
  
  <p>Can someone help me how to set OpenCV 4 in cv_bridge (ROS melodic system)?</p>
  
  <p>Thanks in advance.
  Best Regards,
  Jovan.</p>