title: opencv report color differences between images
body: <p>Assume an image A and an image B, where B is a modified copy of A with overall higher HSV-value and lower saturation.
  How can I report these differences using OpenCV? </p>
  
  <p>Ex. output: hue 0, saturation -25, HSV-value +25.</p>
  
  <p>I have already been able to convert the bgr-images to hsv-images and split these into the 3 channels.
  Would it be a good/correct idea to take the average of each channel of both images, and just output the difference of these averages? Or is there perhaps a better or already-included-in-opencv way?
  Thanks!</p>