title: OpenCV error due possibly to different "step"
body: <p>I have converted some code from old Opencv to the c++ version, and I get an error at matrix multiplication.</p>
  
  <pre><code>OpenCV Error: Sizes of input arguments do not match (The operation is neither 
  'array op array' (where arrays have the same size and the same number of channels), 
  nor 'array op scalar', nor 'scalar op array')
  </code></pre>
  
  <p>On the web, this error seems to be associated with having different number of channels - mine are all 1.</p>
  
  <p>What I did find different though is a <strong>"step"</strong> - on one it is 24, on another is 32.</p>
  
  <p>Where is this step ?</p>
  
  <p>I created both input matrices using </p>
  
  <pre><code>cv::Mat YYY(3, 4, CV_64FC1);   // step 32
  cv::Mat XXX(3, 3, CV_64FC1);   // step 24
  </code></pre>
  
  <p>Yet they seem to have different step ?</p>
  
  <p>Could this be the culprit for the error in <code>cv::multiply(XXX,YYY, DDD);</code>  ?</p>
  
  <p>Is it not possible to perform operations (like a mask) between different types ? </p>
  
  <p>Thank you</p>