Expand homography matrix for distortion

5
votes

I have two set of corresponding matches that I want to compute Homography Matrix between them. However, I found that the transformation between this points can not be modeled using just the Homography Matrix. I figured this by observing some lines in the original set of points have not represented as lines in the second set.

For example:

enter image description here

The previous state is very extreme in real the distortion is much less than that. It is usually a distortion because of the first set of points were extracted from image that was taken by scanner where the other set of points were extracted from a photo taken by mobile phone.

The Question:

How can I expand or Generalize the Homography matrix to make it includes this case? Or in other words, I want a non-line-preserve transformation model to use it instead of the Homography Matrix, Any Suggestion?

P.S OpenCV library is prefered if there is something ready to use.

EDIT:

Eliminating the distortion may not be an option for me because the photos are somewhat complex and I do not have the same Camera always plus I supposed to deal with images from unknown source (back-end separated from front-end). However, I have a reference which is planner and a query which has perspective + distoration effect which I want to correct it after I could found the corresponding pair matches.

1
opencvcomputer-visiontransformationhomography

1 Answers

2
votes

It would be better if you had provided some examples of your images, so that we can understand your case better. From the description it seems that you are dealing with camera distortion.

Typical approach is to perform camera calibration once, then undistort each frame and finally work with images where straight lines look straight. All of these tasks are possible with OpenCV, consider the link above.

In case you cannot perform camera calibration to estimate distortion - there isn't much you can do. Try to calculate and apply homography on unrectified images - if the cameras don't have wide angle lens this should look ok (consider this case for example)