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My inputs are several binary images like:first binary image to be registersecond binary image to be register

They have globally the same content but may be unregistered as they are produced from a hand camera. What I would like to compute is the 2D displacement vector from the first image to the second. I use OpenCV and my first attempt was to compute feature points (SURF algorithm) and the affine transform between both images. But of course, feature description are kinda poor on a binary image, therefore the matching is difficult and the matching map very inaccurate.

Does anyone has an idea how I could do this?

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I am somewhat surprised that feature points don't work that well. I have had success registering shapes like yours using either

  • Harris points, this is a corner detector, in combination with the RANSAC algorithm. See the wiki or Peter Kovesi his site
  • Using a feature detector like SURF or SIFT in combination with an edge map of the image prior to feature detection followed by some form of robust matching.

EDIT

I gave it a go with matlab and tried some variations on this theme. Currently I use

  • SIFT features from the edge map to ascertain rotation and scaling, although they are very small between the images you provided
  • RANSAC for robust matching
  • Cross correlation to ascertain the translation between the two images

Robust match Before registration After registration

Source on github.

An alternative for RANSAC could be the Hough transform voting/binning approach that was proposed by the inventor of SIFT, David Lowe.

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  • $\begingroup$ I know Harris, but I don't have fast and robust matching algorithm to be sure I get the same points from one image to another. Plus, Ransac is not usable as is in OpenCV... $\endgroup$ – Stéphane Péchard Jan 13 '12 at 9:45
  • $\begingroup$ Thanks a lot for your effort. It shows a nice way to perform this. I finally modified the way I do what I need to do, because features computation and matching is too CPU-intensive for me. Thanks anyway, you did a good job! $\endgroup$ – Stéphane Péchard Jan 17 '12 at 8:57
  • $\begingroup$ Stephane, could you please add your solution as well to the site? $\endgroup$ – Maurits Jan 17 '12 at 10:45
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    $\begingroup$ well, the thing is I don't answer to the question asked so it's not relevant to put that here. What I did is a detection of the blobs of the image and a description of each blob by the minimum amount of points possible. I wanted the 2D displacement to compute a temporal accumulation, but I won't do that anymore, as a vectorial description of the blobs is sufficient. $\endgroup$ – Stéphane Péchard Jan 18 '12 at 9:20

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