opencv - Are there any fast alternatives to SURF and SIFT for scale-invariant feature extraction?

Question

SURF is patented, as is SIFT. ORB and BRIEF are not patented, but their features are not scale-invariant, seriously limiting their usefulness in complex scenarios.

Are there any feature extractors that can extract scale-invariant features as fast as SURF and are not so strictly patented as SURF and SIFT?

Answer 1

Although you already choose BRISK, you might find FREAK interesting. Author claims to have better results than BRISK and ORB. I should also add that ORB is scale-invariant but has some problems in that area. So I would still recommend it for someone to try it.

The FREAK source code is compatible with OpenCV (how easy it is to merge them I do not know) and the author is working on submitting it to the OpenCV project.

EDIT:

FREAK is now part of opencv feature detectors / descriptors.

You can read here more about the differences between several feature detectors/extractors, and also a series of benchmarks which includes FREAK and other popular ones.