title: What's the significance of a negative NCC coefficient w.r.t. image template matching?
body: <p>I have been using Matlab's normxcorr2 function to do template matching with images by performing normalized cross correlation. To find the maximum correspondence between a template and an image, one can simply run normxcorr2 and then find the maximum <em>absolute</em> value of all the values returned by normxcorr2 (the function returns values between -1.0 and 1.0).</p>
  
  <p>From a quick Google search, I found out that a negative correlation coefficient means an inverse relationship between two variables (e.g. as x increases, y decreases), and that a positive correlation coefficient means the opposite (e.g. as x increases, y increases). <strong>How does this apply to image template matching?</strong> That is, what does a negative value from normxcorr2 mean <em>conceptually</em> with respect to template matching?</p>