ORB

ORB (Oriented FAST and Rotated BRIEF) (RRKB11) combines the FAST keypoint detector with the BRIEF descriptor, modified to be rotation invariant. Since FAST does not provide orientation information, ORB computes it by finding the intensity centroid within the patch around the keypoint: the vector from the point to the centroid is rotation invariant and sufficiently robust to changes in illumination.

Using this angle, ORB rotates the BRIEF pattern (using precomputed rotated patterns, for example by quantizing the full circle into 30 sectors) to generate a rotation-robust binary descriptor known as rBRIEF. Applying FAST and BRIEF at different levels of an image pyramid also provides scale invariance.

ORB offers accuracy comparable to SIFT and SURF, but is significantly faster and, above all, unencumbered by patents.