Howtosignalprocessing
- How is homography matrix calculated?
- How to calculate homography matrix in OpenCV?
- Why do you need 4 points for homography?
How is homography matrix calculated?
What is the homography matrix? The homography matrix is a 3x3 matrix but with 8 DoF (degrees of freedom) as it is estimated up to a scale. It is generally normalized (see also 1) with h_33 = 1 or h_11^2 + h_12^2 + h_13^2 + h_21^2 + h_22^2 + h_23^2 + h_31^2 + h_32^2 + h_33^2 = 1 .
How to calculate homography matrix in OpenCV?
How to calculate a Homography ? To calculate a homography between two images, you need to know at least 4 point correspondences between the two images. If you have more than 4 corresponding points, it is even better. OpenCV will robustly estimate a homography that best fits all corresponding points.
Why do you need 4 points for homography?
Given that 1 point-to-point correspondence represents 2 constraints, then 4 point-to-point correspondences corresponds to 8 constraints. Given this and given that homographies have 8 degrees of freedom, at least 4 point-to-point correspondences are necessary to estimate a homography.
