How many pairs of points are necessary for the correct calculation of homography?

Question

in order to get homography between two images, I wanted to know how many points do I need, at least to get a good score for the homography matrix?

Answer 1

You need at least four to get anything at all, but I found 7 to 10 to be a good number in practice, provided they are selected “manually”. Using some kind of function detector, you may need ten or 20 times to find a suitable subset with multiple outliers.

In fact, it depends on the distribution of points - if you have 10 linear points, you will not get a happy result, for example. However, for a slightly distorted rectangular display, all four corners are all you need.