title: Measure difference of two images using emgucv
body: <p>i need to compare two images and identify differences on them as percentage. "Absdiff" function on emgucv doesn't help with that. i already done that compare example on emgucv wiki.  what i exactly want is how to get two image difference in numerical format?</p>
  
  <pre><code>//emgucv wiki compare example
  
  //acquire the frame
  Frame = capture.RetrieveBgrFrame(); //aquire a frame
   Difference = Previous_Frame.AbsDiff(Frame);
  //what i want is
  double differenceValue=Previous_Frame."SOMETHING";
  </code></pre>
  
  <p>if you need more detail plz ask.
  Thanks in advance.</p>