title: matrix type conversion in opencv
body: <p>I am trying to convolve an image with a filter and storing it to a matrix of type CV_64F with the help of filter2D function in opencv. but the type of the destination matrix get changed and i try to change it back to CV_64F with the help of assignTo 0r ConvertTo function but i am not able to do so. Can someone help? This is lines of my code</p>
  
  <pre><code>                     cv::Mat op = cv::Mat(25,25,a.type(),Arr1); // a is the image matrix and op is the filter.
           cv::Point anchor = Point(-1,-1);
           cv::Mat b = cv::Mat(a.size(),CV_64F);
           cv::Mat l = cv::Mat(a.size(),CV_64F);
           cv::Mat m = cv::Mat(a.size(),CV_64F);
  
          //prnmt(a);
  
           filter2D(a,b,-1,op,anchor,0,BORDER_DEFAULT);
           b.assignTo(l,CV_64F);
  </code></pre>