title: What methodology/algorithm does cv::absdiff() use?
body: <p>What methodology/algorithm does OpenCV's <code>cv::absdiff(InputArray src1, InputArray src2, OutputArray dst)</code> use? </p>
  
  <p>For a 1 channel <code>Mat</code> does it compute the colour distance between each cell/voxel of <code>src1</code> with the voxel at the same position of <code>src2</code>? Does it compute the intensity difference or colour difference or other? Is it's worst-case, average and best-case runtime O(N) (where N is the number of voxels in the <code>Mat</code>)? How is the absolute difference calculated?</p>
  
  <p>In terms of runtime complexity is <code>cv::canny()</code> slower or faster than <code>cv::absdiff()</code>? Is the speed difference significant?</p>