title: Conversion from pixel to general Metric(mm, in)
body: <p>I am using openCV to process an image and use houghcircles to detect the circles in the image under test, and also calculating the distance between their centers using euclidean distance.
  Since this would be in pixels, I need the absolute distances in mm or inches, can anyone let me know how this can be done</p>
  
  <p>Thanks in advance.</p>